JPH10322215A - Signal transmission method by means of 1-bit digital signal, delta sigma modulation circuit and demodulation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a signal transmission method where a subsignal is superimposed on a main signal with a simple circuit and the superimposed signal is transmitted by means of a 1-bit digital signal and to provide a delta sigma modulation circuit and a demodulation circuit. SOLUTION: In the delta sigma modulation circuit 31, an input signal is integrated in high degree by integration devices m1-m7. All outputs from the integrators of each degree are added by an adder 13, the sum is quantized by a quantizer 14, which provides an output of a 1-bit digital signal. A dip is formed at a prescribed zero point frequency in a quantized noise frequency characteristic of the 10-bit digital signal by a partial negative feedback loop consisting of feedback circuits m11-m13. Furthermore, an additional information signal generating circuit 21 generates a signal whose carrier frequency is the zero point frequency as channel information and gives the signal to the adder 13. The channel information is superimposed on the main signal in terms of the 1-bit digital signal through frequency division multiplexing at the zero point frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal transmission method using delta sigma modulation, a delta sigma modulation circuit, and a signal generated by delta sigma modulation, which are particularly preferably used for audio signal processing. The present invention relates to a bit digital signal demodulation circuit.

[0002]

2. Description of the Related Art Conventionally, as a method of transmitting a digital signal, a multi-bit encoding method in which one word composed of a plurality of bits is transmitted as a delimiter and a 1-bit digital signal using delta-sigma modulation have been used. A transmission method is known.

[0003] In the case of the multi-bit encoding method, the transmitting or recording side transmits one data according to a predetermined format.
Encode to words. On the other hand, the receiving or reproducing side establishes word synchronization to determine the delimitation of each word, and decodes each word to identify data. Therefore, a signal processing circuit that performs signal processing according to the word format is required on both sides. As a result, once the word format is determined and the sampling frequency, dynamic range, etc. are standardized, it is difficult to change the standard. Furthermore, since the method requires word synchronization,
An error correction circuit for correcting an error that is easily affected by a transmission path or the like is indispensable.

On the other hand, in the 1-bit digital encoding method, since the 1-bit digital signal is a finely divided data flow that does not require word synchronization, the 1-bit digital signal is hardly affected by a transmission path or the like, and is less susceptible to errors. It has the advantage of being strong.
Therefore, in this system, an error correction circuit is not required in both the transmitting or recording device and the receiving or reproducing device. Further, when the 1-bit digital signal is an audio signal, the receiving or reproducing side can demodulate the 1-bit digital signal into an analog signal by a simple low-order low-pass filter, thereby eliminating the need for a complicated processing circuit for demodulation. Become. Therefore, in recent years, a 1-bit digital encoding scheme, which has many advantages as compared with a multi-bit encoding scheme, has attracted attention.

As shown in FIG. 12, in a conventional typical delta-sigma modulation circuit 100, an analog audio signal input from an input terminal 101 is integrated by integrators m101 to m107 connected in cascade. . After the outputs of the integrators of each stage are added by the adder 103, the quantizer 10
4 is input. The quantizer 104 derives an output of “1” to the output terminal 106 when the output of the adder 103 is 0 or more, and derives an output of “0” when the output of the adder 103 is less than 0. The output of the quantizer 104 is negatively fed back to the input side of the first-stage integrator m101 via the digital / analog converter 105 and the feedback resistor r100.

On the other hand, a dip is formed in the noise floor of the 1-bit digital signal output from the delta-sigma modulation circuit 101 and the integration circuit 10 of the delta-sigma modulation circuit 101 is adjusted in order to adjust the noise floor shape to a desired shape.
2, two feedback circuits m111 to m113 are provided. The feedback circuit m111 includes a third-stage integrator m10.
3 is negatively fed back to the input side of the second-stage integrator m102, and the feedback circuits m112 and m113 output the outputs of the fifth and seventh-stage integrators m105 and m107 to the fourth and sixth stages, respectively. Negative feedback is provided to the input sides of the integrators m104 and m106 of the eyes.

The feedback circuits m111 to m113 form three partial negative feedback loops. The quantization noise level of the 1-bit digital signal is centered on a frequency (zero frequency) corresponding to the gain of each partial negative feedback loop. And drops sharply. In the following, a portion of the frequency characteristic of the quantization noise whose level is reduced is referred to as a dip. By these dips, high-frequency quantization noise is suppressed, and the level of the quantization noise can be kept at a predetermined value or less, for example, up to the upper limit of a desired use frequency band such as 20 kHz.

After the audio signal is modulated into a 1-bit digital signal in the delta-sigma modulation circuit 100, the 1-bit digital signal is transmitted to a receiving or reproducing device (not shown) by, for example, a low-order low-pass filter. It is demodulated to an analog audio signal.

[0009]

However, when modulated using the delta-sigma modulation circuit 100 having the above configuration, both the main signal such as an audio signal and the sub-signal such as a flag indicating channel information are transmitted. It is difficult to do this.

Here, as a conventional method for transmitting both a main signal and a sub-signal, a case of a signal transmission method in a multi-bit encoding system will be described as an example. In the following, a method of transmitting or recording and reproducing a main signal and a sub signal using digital audio such as a compact disc will be described as an example of a typical conventional multi-bit encoding method.

In the case of a compact disk, the sampling frequency Fs is set to 44.1 kHz, and FIG.
As shown in FIG. 3, the upper limit frequency Fa of the audio band is １ ／.
Fs, that is, 22.05 kHz. Where F
In the frequency band from a to Fs, the signal in the voice band is F
Since the mirror image is inverted at a and turned back, this band (turned area) cannot be used for signal transmission. Therefore, when a sub-code such as a flag for identifying the left or right channel is transmitted as a sub-signal together with the audio signal as the main signal, the sub-code is transmitted in time together with the main data indicating the audio signal. It is split and transmitted in the axial direction.

As a result, on the transmitting or recording side, a circuit for encoding the flag and the audio signal in accordance with the standardized data format is required, and on the receiving or reproducing side, the received or reproduced data is encoded. A circuit for decoding and separating the main data and the subcode is required.

The method of transmitting the main data and the subcode in a time-division manner impairs the advantage of the 1-bit digital encoding system that it can be demodulated by a simple circuit.
It cannot be applied to bit digital encoding.

The present invention has been made in view of the above problems, and has as its object to provide a signal transmission method via a 1-bit digital signal which can be transmitted by superimposing a sub signal on a main signal with a simple circuit. , A delta-sigma modulation circuit, and a demodulation circuit.

[0015]

According to the first aspect of the present invention, there is provided:
In order to solve the above-mentioned problem, a signal transmission method via a bit digital signal converts a main signal having a predetermined effective frequency into a quantization noise at a predetermined specific frequency within the effective frequency band using zero point control. Delta-sigma modulation so as to decrease and modulate to a 1-bit digital signal;
A signal transmission method via a 1-bit digital signal, comprising: a transmission step of transmitting a 1-bit digital signal via a transmission path or a recording medium; and a step of demodulating the transmitted 1-bit digital signal. It is characterized by having a process.

That is, before the transmission step, a sub-signal is superimposed on the main signal of the 1-bit digital signal by frequency division multiplexing at the specific frequency, and after the transmission step, the 1-bit digital signal is superimposed. Discriminating the specific frequency of the signal to extract the sub-signal.

In the above configuration, on the modulation side, for example,
A main signal provided as an analog signal, a multi-bit digital signal, or the like is delta-sigma modulated into a 1-bit digital signal. At this time, the quantization noise level of the 1-bit digital signal is reduced at a predetermined specific frequency within the effective frequency band of the main signal due to the zero point control.

Further, on the modulation side, a sub-signal is superimposed on the 1-bit digital signal by frequency division multiplexing via a carrier wave of a specific frequency. At the specific frequency, the quantization noise level is reduced, so the level difference between the quantization noise level and the lower limit of the level of the main signal is larger than the neighboring frequency in the effective frequency band. Yes,
At the specific frequency, both the dynamic range of the main signal and the dynamic range of the sub signal can be secured.

On the other hand, when the 1-bit digital signal is transmitted via a transmission path or a recording medium, the demodulation side demodulates the main signal from the received 1-bit digital signal. For example, when the main signal is an audio signal, the main signal included in the 1-bit digital signal is demodulated by passing through a simple low-order low-pass filter.

Further, on the demodulation side, a specific frequency component of the 1-bit digital signal is discriminated by using, for example, a band-pass filter or a Fourier transform, and a sub-signal is extracted. As described above, since the dynamic range of the main signal and the dynamic range of the sub-signal are sufficiently ensured, the sub-signal can be extracted without any trouble on the demodulation side.

In the above-described signal transmission method using a 1-bit digital signal, since the sub-signal is superimposed on the main signal by frequency division multiplexing, a complicated configuration required for transmission by time division multiplexing or the like is required. And a circuit for signal processing can be simplified. As a result, the main signal and the sub-signal can be superimposed without impairing the advantage of transmitting the signal as a 1-bit digital signal.

The specific frequency is set within the effective frequency band of the main signal. Therefore, a third party who does not know the specific frequency cannot separate the main signal and the sub signal. For example, even if a third party discriminates only the effective band component of the main signal from the 1-bit digital signal, the discriminated signal includes both the main signal and the sub-signal. Further, since the frequency division multiplexing is used, it is difficult to separate the main signal and the sub signal compared to the case where the time division multiplexing is used. As a result, falsification of the sub signal by a third party can be prevented.

According to a second aspect of the present invention, there is provided a delta-sigma modulation circuit, comprising: a plurality of integrators which receive an input signal as a main signal at an initial stage and are connected in cascade with each other; An adder for adding the output of the integrator; a quantizer for quantizing the output of the adder to output a one-bit digital signal; and an output of the integrator to an input of an integrator preceding the integrator. A partial negative feedback circuit that negatively feedbacks to the side to reduce the quantization noise of the 1-bit digital signal at a predetermined specific frequency. It is characterized by having a sub-signal superimposing means for superimposing a sub-signal on a main signal by frequency division multiplexing.

In the above configuration, the input signal is delta-sigma modulated into a 1-bit digital signal by the integrator, the adder, the quantizer, and the partial negative feedback circuit. The sub-signal superimposing unit superimposes the sub-signal on the main signal of the 1-bit digital signal by frequency division multiplexing, for example, by inputting a signal of a specific frequency generated based on the sub-signal to the adder. I do.

The specific frequency is set by the gain of a partial negative feedback loop formed by an integrator, a partial negative feedback circuit, and the like, and the level of quantization noise of a 1-bit digital signal decreases at the specific frequency. . Therefore, at the specific frequency, both the dynamic range of the main signal and the dynamic range of the sub-signal can be ensured.

Therefore, a delta-sigma modulation circuit capable of modulating a main signal and a sub-signal into a 1-bit digital signal without obstructing the feature of the delta-sigma modulation that demodulation is easy as in claim 1 is provided. Can be provided. Further, since the delta-sigma modulation circuit superimposes the sub-signal within the effective frequency band of the main signal, it is difficult to remove or alter the sub-signal by a third party.

According to a third aspect of the present invention, in the delta-sigma modulation circuit according to the second aspect of the present invention, the sub-signal superimposing means transmits the sub-signal to one of the inputs of the adder. It is characterized by inputting via a carrier wave of a specific frequency.

In the above configuration, the sub-signal superimposing means uses the adder used for delta-sigma modulation also for superimposing the sub-signal. Therefore, a circuit provided for superposition can be simplified.

Further, in the delta-sigma modulation circuit according to a fourth aspect of the present invention, in the configuration of the second or third aspect, the main signal is an audio signal, and the sub-signal is
It is a signal indicating at least one of channel information, presence / absence of pre-emphasis, a flag for copyright protection, an ID code, a mastering code, and time information.

In the above configuration, the information serving as the sub-signals is information that is closely related to the audio signal serving as the main signal and has a small amount of information. Therefore, even if the level difference between the quantization level at the specific frequency and the lower limit of the main signal level is small, that is, even if the dynamic range of the sub signal cannot be made too wide, the sub signal can be provided with a sufficient S / N. Can be superimposed and transmitted or recorded. As a result, on the demodulation side, processing related to the main signal, such as control of channel separation and pre-emphasis, can be performed based on the sub signal.

According to a fifth aspect of the present invention, there is provided a demodulation circuit for converting a main signal having a predetermined effective frequency band to a predetermined specific frequency within the effective frequency band by using zero point control. In a demodulation circuit for demodulating a 1-bit digital signal generated by performing delta-sigma modulation so as to reduce quantization noise, a main signal of the 1-bit digital signal includes a sub signal via a carrier wave of the specific frequency. The apparatus is characterized by comprising control means for superimposing by frequency division multiplexing, extracting the sub-signal by discriminating the specific frequency component from the 1-bit digital signal, and performing predetermined processing according to the sub-signal. And

In the above configuration, since the level of the quantization noise of the 1-bit digital signal decreases at a specific frequency, the dynamic range that can be secured at the specific frequency is smaller than that of a neighboring frequency in the effective frequency band. As a result, the S / N of the sub signal can be sufficiently secured.
Therefore, the control means extracts the sub-signal superimposed on the 1-bit digital signal by discriminating the specific frequency component.
A predetermined process can be performed. Further, since the sub-signal is superimposed by frequency division multiplexing, the demodulation circuit can demodulate the main signal more easily than when superimposing by time division multiplexing.

According to the fifth aspect of the present invention, the control means monitors the level of the main signal, and extracts the sub signal when the level is lower than a predetermined value.
Even when the dip cannot be formed too deeply, that is, even when the quantization noise level at a specific frequency does not decrease so much, the sub-signal can be reliably extracted.

The demodulation circuit according to the invention of claim 6 is:
In the configuration of the invention according to claim 5, the main signal is an audio signal, the sub-signal is channel information indicating a channel of the audio signal, and the control unit is configured to execute It is characterized by performing left / right or multi-channel separation.

Therefore, the demodulation circuit can correctly determine the channel of the audio signal. Therefore, even when the demodulation circuit receives a 1-bit digital signal of an unusual channel, for example, when the transmission path for transmitting the 1-bit digital signal of each channel is switched, the demodulation circuit is not affected. Can separate left and right or multi-channel without any problem. As a result, the demodulation circuit
For example, audio signals can be sounded, or
When recording or transmission is performed, the demodulation circuit can output an audio signal or the like on a correct channel.

On the other hand, the demodulation circuit according to the seventh aspect of the present invention
In the configuration according to the fifth aspect of the present invention, the main signal is an audio signal, the sub-signal is a flag indicating the presence or absence of pre-emphasis of the audio signal, and the control unit is configured to execute the control based on the flag. , On / off control of de-emphasis.

Therefore, the demodulation circuit can reliably determine whether or not the received 1-bit digital audio signal is a signal subjected to the pre-emphasis processing, and apply the de-emphasis to the audio signal.

Further, in the demodulation circuit according to the present invention, the main signal is an audio signal, and the sub-signal is for protecting the copyright of the audio signal. And the control means restricts copying or demodulation output of the audio signal based on the sub-signal and at least one of a flag, an ID code, and a mastering code.

In the above arrangement, the control means extracts a sub-signal from the 1-bit digital signal, and limits the copying or demodulation output of the audio signal when the sub-signal does not permit copying or demodulation output. For example, when the modulation side superimposes a flag for copyright protection as a sub-signal for the purpose of, for example, protecting the copyright of an audio signal, the modulation side,
Depending on the intention of the creator of the audio signal, copying or demodulation of the audio signal on the demodulation side is restricted. Also, when an ID code for distinguishing an audio signal or a mastering code for identifying the type of the audio signal is superimposed as a sub-signal, the demodulation side itself, based on these sub-signals, It is determined whether or not copying or demodulation output is permitted. If not, the copying or demodulation is restricted. In any case, since the control means limits the copying or demodulation output of the audio signal based on the sub-signal, the modulation side can specify permission / non-permission of the copying or demodulation output on the demodulation side.

By the way, if the above-mentioned sub-signal is falsified before the 1-bit digital signal is received, the demodulation circuit cannot limit the copying or demodulation output of the audio signal. Therefore, conventionally, in order to prevent tampering of the sub-signal, the tampering of the sub-signal is prevented by, for example, encrypting the sub-signal. However, this method requires a complicated circuit such as a sequential circuit for encryption and decryption.

On the other hand, in the configuration of the present invention, the sub-signal is frequency-division multiplexed at a specific frequency within the effective frequency band of the audio signal. Therefore, a third party who does not know the specific frequency cannot even separate the sub-signal and the main signal and cannot easily tamper with it. As a result, as compared with a conventional sub-signal transmitted by time division multiplexing,
It is difficult to falsify. Further, since the specific frequency is provided in the effective frequency band, if a certain frequency component is carelessly removed, the audio signal changes. Therefore,
Alteration of the sub-signal can be prevented more reliably. As a result, the demodulation circuit can reliably limit the copying or demodulation output of the audio signal based on the permission / non-permission of the copying or demodulation output instructed on the modulation side.

It should be noted that the sub-signals adopted in the configuration of the invention according to claims 6 to 8, ie, channel information,
Pre-emphasis, flag for copyright protection,
Each of the ID code and the mastering code has a small amount of information, and can be indicated by a small bit flag. Therefore, the demodulation circuit according to claims 6 to 8 can reliably identify the sub-signal even if the dynamic range that can be secured for the sub-signal is relatively narrow.

[0043]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] An embodiment of the present invention will be described below with reference to FIGS. That is, the audio signal transmission device according to the present embodiment is a device that transmits an audio signal as a main signal, and determines whether the audio signal is a left or right channel as a sub-signal that is multiplexed with the main signal by frequency division. The channel information shown is used.

As shown in FIG. 2, the audio signal transmission apparatus 1 converts the analog or multi-bit audio signals output from the left and right channel audio signal sources 2L and 2R into a transmission circuit 3
After performing delta-sigma modulation on the 1-bit digital signal by using the transmission circuit 4L or 4R such as an optical fiber, the signal is transmitted to a receiving circuit (demodulation circuit) 5, and the receiving circuit 5 transmits the 1-bit digital signal. Is demodulated and the amplifier 6L
The sound is made from the left and right channel speakers 7L and 7R via 6R. Here, the transmission lines 4L and 4L
In order to accurately discriminate the audio signals of each of the left and right channels and to demodulate and output the audio signals in response to the exchange of R, for example, one of the transmission circuits 3 (here, the left channel) outputs channel information serving as a sub signal. Is frequency-division multiplexed into a main audio signal. In the following, when referring to each member, if there is no particular distinction between left and right, or when both are collectively referred to, the alphabetic character (R or L) added to the end of the reference numeral is omitted, and for example, an audio signal source Reference like 2.

As shown in FIG. 1, the delta-sigma modulation circuit 31 includes an integration circuit 12 for integrating the analog audio signal input from the audio signal source 2 to the input terminal 11 at a higher order.
, An adder 13 for adding the next-order integrated output, and an adder 1
3, a quantizer 14 for quantizing the output of 3 and outputting a 1-bit digital signal, a digital / analog converter 15 for converting the output of the quantizer 14 to an analog value and feeding it back to the integrating circuit 12 It has.

The quantizer 14 samples the output of the adder 13 at a predetermined sampling frequency FS, and derives an output of “1” when the output is greater than or equal to 0, and derives an output of “0” when the output is less than 0. Derive the output. As a result, a 1-bit digital signal of the sampling frequency FS is output from the output terminal 16.

In a 1-bit digital encoding system for sampling a multi-bit digital signal at high speed, a quantizer 1
The sampling frequency FS of 4 is usually set to a predetermined multiple of fs, such as 32 fs or 64 fs, where fs is the sampling frequency of the multi-bit digital signal. Here, as in the case of a compact disc, f
Assuming that s = 44.1 kHz, FS is 1.41 MHz at 32 fs, and 2.82 MH at 64 fs.
z.

On the other hand, the integrating circuit 12 includes cascaded seventh-order integrators m1 to m7 and feedback circuits (partial negative feedback circuits) m11 to m13 for forming a partial negative feedback loop.
And a feedback resistor r0 provided between the input side of the first-stage integrator m1 and the digital / analog converter 15. The feedback resistor r0 is connected to an inverting input terminal of a differential amplifier a1 described later.

The first-order integrator m1 is a differential amplifier a1
A capacitor c1 as a time constant element provided between the input and output of the differential amplifier a1, and an input resistor r1 provided between the input of the integrator m1 and the inverting input terminal of the differential amplifier a1. It has. The non-inverting input terminal of the differential amplifier a1 is grounded. The output from the differential amplifier a1 is used as the output of the integrator m1 as an integrator m2 in the next stage.
And the adder 13.

The integrators m2 to m7 at the next and subsequent stages have the same configuration, and the reference numerals of the corresponding parts are the same alphabetical characters with the addition of a subscript corresponding to the order of each of the integrators m2 to m7. Is shown. For example, in the third-order integrator m3, the output of the integrator m2 is input via the input resistor r3, and the output of the differential amplifier a3 is input to the next-stage integrator m4 and the adder 13.

The feedback circuit m11 is provided in association with the second-order integrator m2 and the third-order integrator m3, and outputs the output of the integrator m3 to the input side of the integrator m2. Negative feedback can be provided. Specifically, the feedback circuit m11 includes a differential amplifier a11 and the differential amplifier a11.
Ri11 whose one end is connected to the inverting input terminal of
And a feedback resistor rf11 provided between the input and output of the differential amplifier a11, and an output resistor ro11 having one end connected to the output of the differential amplifier a11. The input resistance ri
The other end of the output resistor ro11 is connected to the input of the feedback circuit m11, that is, the output of the integrator m3.
Is the output of the feedback circuit m11, that is, the integrator m
2 is connected to the inverting input terminal of the differential amplifier a2 provided in the second amplifier 2. The non-inverting input terminal of the differential amplifier a11 is grounded. Similarly, a feedback circuit m12 is provided in association with the fourth-order integrator m4 and the fifth-order integrator m5, and a sixth-order integrator m6 and a seventh-order integrator m7 are provided. In connection therewith, a feedback circuit m13 is provided. Since the configuration of both feedback circuits m12 and m13 is the same as the configuration of feedback circuit m11, the reference numerals of the corresponding parts are denoted by the same alphabetical characters and the same subscripts as those of feedback circuits m12 and m13. ing.

The feedback circuits m11 to m13 form three partial negative feedback loops in the integration circuit 12. For example, in a partial negative feedback loop formed by the feedback circuit m11, the output of the integrator m2 is integrated and inverted by the integrator m3, further forward-rotated by the feedback circuit m11, and provided to the integrator m2. Negative feedback is provided to the non-inverting input terminal of the differential amplifier a2.

With these three partial negative feedback loops,
As shown in FIG. 3, three dips are formed in the frequency characteristic of the quantization noise level of the 1-bit digital signal. The center frequency (zero frequency) f of the dip is determined by the loop gain Gp of each partial negative feedback loop, and as shown in the following equation (1), f ≒ FS × (Gp) ^1/2 / 2π (1) ). In the above equation (1), FS is the sampling frequency of the delta-sigma modulation circuit 31. Thus, the quantization noise level of the 1-bit digital signal is
By lowering at each zero frequency, the quantization noise level in a desired frequency band can be suppressed to a certain value or less.

The gain Gp of the partial negative feedback loop is determined by the multiplier coefficient of the differential amplifier forming the partial negative feedback loop. For example, the gain Gp of the partial negative feedback loop formed by the feedback circuit m11 is the differential amplifier a2 · a
It is determined by the product of the multiplier coefficients of 3 · a11. Therefore, these multiplier coefficients are set such that a predetermined dynamic range is maintained in a predetermined frequency band and the zero-point frequency is a desired frequency.

Here, as an example of the above-mentioned frequency band and dynamic range, conditions required in current consumer digital audio equipment are as follows: 10 kHz to 20 kHz.
S in the frequency band of about 90 to 100 dB.
/ N is required to be maintained. Therefore, as shown in FIG. 3, the gain Gp of each of the partial negative feedback loops is set to a value that can secure a desired dynamic range (for example, about 90 dB) in a region of 20 kHz or less.

As described above, the case where the predetermined frequency band is a voice band (usually audible band) will be described as an example. By forming a dip centering on the upper limit of the voice band (around 20 kHz), Can be effectively reduced. In this case, the band in which the dip exists is 1 kHz to 40 kHz.
About. The frequencies (zero-point frequencies) α1, α2, and α3 of the three dips are, for example, as shown in the following equations (2) and (3): α1 = α3 / (2 （2) (2) α2 = α3 / √2 (3)

Further, the delta sigma modulation circuit 31 according to the present embodiment includes an additional information signal generation circuit (sub signal superimposing means) 21 for generating an additional information signal by amplitude-modulating the sub signal with the carrier having the zero frequency. Is provided. The output of the additional information signal generation circuit 21 is applied to the adder 13, and the outputs of the integrators m 1 to m 7 and the sum of the additional information signals are output to the quantizer 14.

In this embodiment, the addition of the additional information signal to the main signal is performed by the adder 1 in the delta-sigma modulation circuit 31.
3 is performed. The adder 13 is an indispensable configuration for delaying the quantized output and negatively feeding back to the input side when performing delta-sigma modulation. By using the adder 13 also for superimposing the additional information signal, The main signal and the sub-signal can be multiplexed and transmitted without adding a special configuration.

In FIG. 1, for convenience of explanation, the case where the integration order is 7 and the number of partial negative feedback loops is three in the delta-sigma modulation circuit 31 has been described as an example. However, the present invention is not limited to this. Absent. With a delta-sigma modulation circuit capable of zero point control, the same effects as in the present embodiment can be obtained.

Here, the correspondence between the sub signal and the additional information signal,
Specifically, how to encode the sub-signal or how to assign a flag having an information amount of how many bits to which zero-point frequency can be variously set.
, Channel information is added only to the 1-bit digital signal of the left channel, and when the three zero frequencies are α1, α2, and α3 from the lower one, if the audio signal is the left channel, the zero frequency A case where a flag is set only for α2 will be described as an example.

In this case, there is one zero frequency corresponding to each channel, and the amount of information added at the zero frequency is one bit. Therefore, the additional information signal generation circuit 21 can be realized by the oscillator 22 that oscillates at a predetermined level at the zero frequency and the switch 23 that selects whether to output the output of the oscillator 22 as the additional information signal.

In the present embodiment, in the delta-sigma modulation circuit 31L on the left channel side, the oscillator 22 has an oscillation frequency set to the second zero-point frequency α2, and the output level is determined from the quantization noise level at the zero-point frequency α2. , Are set to be smaller than the sound signal level up to the lower limit. The switch 23 conducts when the audio signal applied to the delta-sigma modulation circuit 31L is a stereo signal. In addition, for example, when the audio signal is not the left channel, such as a monaural signal,
The switch 23 is turned off.

The audio signal transmission device 1 according to the present embodiment
In order to simplify the configuration for adding the channel information, the channel information is added only to the 1-bit digital signal of the left channel, and is not added to the 1-bit digital signal of the right channel. That is, the delta-sigma modulation circuit 3 of the right channel
The 2R delta-sigma modulates the analog audio signal from the audio signal source 2R as it is. Specifically, as shown in FIG. 4, the delta-sigma modulation circuit 32 has a configuration in which the additional information signal generation circuit 21 is omitted from the delta-sigma modulation circuit 31 shown in FIG. Accordingly, an adder 13a having one less input is used in place of the adder 13 shown in FIG. Since the remaining configuration is the same as that of the delta-sigma modulation circuit 31, members having the same functions are denoted by the same reference numerals and description thereof will be omitted.

Thus, in the transmission circuit 3 shown in FIG. 2, the delta-sigma modulation circuit 31L performs delta-sigma modulation on the analog audio signal output from the audio signal source 2L, and outputs channel information indicating that the channel is the left channel. Are superimposed. As a result, the 1-bit digital signal on which the channel information is superimposed is output from the output terminal 41L. These 1-bit digital signals of the left and right channels are transmitted through transmission lines 4L and 4L.
The signal is transmitted to the receiving circuit 5 via R. In the present embodiment, no channel information is superimposed on the 1-bit digital signal output from the output terminal 41R on the right channel side.

On the other hand, in the transmission circuit 5, the 1-bit digital signal input from the input terminal 42L via the transmission line 4L is transmitted to the channel switching circuit 53 via the demodulation circuit 51L and the low-pass filter 52L. Similarly, the 1-bit digital signal input from the input terminal 42R via the transmission line 4R is applied to the channel switching circuit 53 via the demodulation circuit 51R and the low-pass filter 52R. The channel switching circuit 5
3 and a later-described channel determination circuit 63 correspond to the control means described in the claims.

Each of the demodulation circuits 51 is realized by, for example, a low-pass filter. In this case, the cutoff frequency of the low-pass filter is set to the upper limit frequency Ft of the transmission band that can be transmitted by a 1-bit digital signal. Thereby, the 1-bit digital signal is modulated into an analog signal. The low-pass filter 52 only needs to be able to remove noise components higher than the effective frequency band of the audio signal. Thus, in particular, rather than higher order filters, 1
The following filter is sufficient. This case can be realized, for example, with one resistor and one capacitor.

Further, the cut-off frequency of each low-pass filter 52 arranged at the subsequent stage of each demodulation circuit 51 is set to the upper limit frequency Fa of a band (sound band) for transmitting a sound signal in the transmission band. As a result, in each low-pass filter 52, an audio signal serving as a main signal is extracted from the analog signal, and input to the channel switching circuit 53.

Here, in the high-speed sampling 1-bit encoding method, if the sampling frequency is FS, FS /
It is known that 2 becomes the upper limit frequency Ft of the transmission band, and FS / 6 becomes the upper limit frequency Fa of the frequency band usable as the voice band.

For example, assuming that FS = 32 fs and fs is 44.1 kHz as in the case of a compact disc, Ft = 32 × 44.1 / 2 = 705.6 [kHz] (4) Fa = 32 × 44 .1 / 6 = 235.2 [kHz] (5)

However, when the circuit is actually implemented by hardware, it is difficult to sufficiently reduce the quantization noise in the frequency band up to the upper limit frequencies Ft and Fa. Therefore, the S / N condition required for current consumer digital audio equipment, that is, 10 to 20
The upper limit frequency Ft, so that the S / N at kHz at about 90 to 100 dB can be relatively easily realized.
Realistic values of Fa are about 1/2 to 1/4 of them. Specifically, for example, Fa is set to about 50 kHz, and Ft is set to about 120 kHz. When the sampling frequency FS is increased to 64 fs, each of the upper limit frequencies Fa and Ft becomes 100 kHz.
z, about 240 kHz.

The channel switching circuit 53
Specifically, switches s1 and s2 that are realized by a relay, an analog switch, or the like and select one of two outputs and output one input are provided. The common contact s1C of the switch s1 is a low-pass filter 52L.
And the common contact s2C of the switch s2 is
It is connected to the low-pass filter 52R. Also, one individual contact s1L of the switch s1 and one individual contact s2L of the switch s2 are commonly used as the left channel amplifier 6L.
Is connected to the speaker 7L via the. Similarly, the remaining individual contacts s1R and s2R of both switches s1 and s2 are commonly connected to a speaker 7R via an amplifier 6R of the right channel. The switches s1 and s2 are switched in response to an instruction from a channel determination circuit 63 described later. As a result, the receiving circuit 5 switches the speakers 7 of both channels.
When outputting an analog audio signal to the L.7R, it is possible to select whether or not to switch the left and right channels.

Further, in order to extract the sub-signal superimposed on the 1-bit digital signal, that is, the channel information,
The receiving circuit 5 is connected to the outputs of the demodulation circuits 51L and 51R, based on the band-pass filters 62L and 62R whose center frequencies are set to the zero-point frequency α2 and the outputs of the band-pass filters 62L and 62R. A channel discriminating circuit 63 for controlling the channel switching circuit 53
L · 63R is provided.

Each of the band-pass filters 62 only needs to be able to remove noise in a band other than the zero-point frequency α2, and channel information is extracted by a channel discriminating circuit 63. Therefore, it can be realized with a first-order filter without using a higher-order filter.

Further, a left-channel channel discriminating circuit 63
L Fourier-transforms the output signal of the band-pass filter 62L, and when the frequency α2 component exceeds a predetermined value, determines that the flag indicating the left channel is set.
Further, when the channel determination circuit 63L determines that the flag indicating the left channel is set, the individual contact s1L side of the switch s1 in the channel switching circuit 53 is turned on, and the individual contact s2R side of the switch s2 is connected. Make it conductive. On the other hand, the channel determination circuit 6 for the right channel
3R, like the channel discrimination circuit 63L, judges that the flag indicating the left channel is set when the frequency α2 component of the output signal of the band-pass filter 62R exceeds a predetermined value. Contrary to the case of 63L, the switch s1 in the channel switching circuit 53 is made to select the individual contact s1R side, and the switch s2 is made to select the individual contact s2L side.

Here, when it is not necessary to always extract the superimposed sub-signal, such as when channel information is superimposed as a sub-signal, each channel discriminating circuit 63 extracts the sub-signal at a specific time. This can further improve the accuracy in separating the main signal and the sub signal.

More specifically, each channel discriminating circuit 63
The output signal level of the band-pass filter 62 is monitored in a narrow band adjacent to the frequency where the sub-signal exists, and 1
The level of the main signal in the bit digital signal is monitored. For example, the channel discriminating circuit 63 extracts the sub-signal during a period in which the output signal level in the narrow band does not reach a predetermined level, such as when there is no input signal or a minute input signal.

The frequency of the sub-signal is fixed at the zero-point frequency determined by the zero-point control, and its spectrum is not spread to adjacent bands. On the other hand, the spectrum of a main signal such as an audio signal is spread as compared with the sub signal. As a result, by determining the input signal level in a narrow band adjacent to the zero-point frequency, it is possible to accurately determine a period in which the level of the main signal is falling near the zero-point frequency. Therefore, during this period, the main signal and the sub-signal can be more accurately separated by the channel discriminating circuit 63 extracting the sub-signal.

For example, in a compact disc of the multi-bit encoding system, the recordable dynamic range is 1
00 dB. On the other hand, the shape of the quantization noise floor is
The integration circuit 12 in the delta-sigma modulation circuit 31 shown in FIG.
Varies greatly depending on the constants of the elements that make up
For example, when the sampling frequency FS of the delta-sigma modulation circuit 31 is 64 fs, the S / N can be reduced to about -120 dB or less. Therefore, the threshold value of the input signal level can be set to about -120 dB.

The signal monitored by the channel discriminating circuit 63 is not limited to the output signal of the band-pass filter 62, but may be, for example, the output signal level of the demodulating circuit 51. If the main signal level in the narrow band can be identified, the same effect as in the present embodiment can be obtained.

The operation of each section of the audio signal transmitting apparatus 1 having the above configuration will be described below with reference to FIG. That is, the analog audio signal of the left channel generated by the audio signal source 2L is input to the transmission circuit 3. In the transmission circuit 3, the sine wave signal of the carrier frequency α2 generated by the oscillator 21a in the additional information signal generation circuit 21 is added to the audio signal in the delta-sigma modulation circuit 31L as channel information indicating the left channel. Vessel 13 (FIG. 1)
See)). Further, the added signal is subjected to delta-sigma modulation and output to the transmission path 4L. On the other hand, the audio signal of the right channel is generated by the audio signal source 2R, is directly delta-sigma-modulated into a 1-bit digital signal by the delta-sigma modulation circuit 32R in the transmission circuit 3, and is output to the transmission path 4R.

If the transmission lines 4L and 4R are correctly connected, the 1-bit digital signal of the left channel is input to the input terminal 4 for the left channel in the receiving circuit 5.
2L, the 1-bit digital signal of the right channel is input to the input terminal 42R. The 1-bit digital signal input from the input terminal 42L for the left channel is demodulated by the demodulation circuit 51L and the low-pass filter 52L, and then an audio signal component is extracted. Further, the output signal of the demodulation circuit 51L is applied to a band-pass filter 62L and a channel discrimination circuit 63L, and it is determined whether or not a preset frequency α2 component exceeds a predetermined level. Similarly, the demodulation circuit 51R and the low-pass filter 52R perform demodulation and audio signal component extraction on the 1-bit digital signal input from the input terminal 42R.

Here, a 1-bit digital signal of the left channel, that is, a signal in which channel information is superimposed by frequency division multiplexing at the frequency α2 is correctly input to the input terminal 42L. Therefore, the channel determination circuit 63L determines that the channel information indicating the left channel is superimposed on the 1-bit digital signal, and controls the switches s1 and s2 in the channel switching circuit 53. Note that the 1-bit digital signal of the right channel includes
Since the channel information is not superimposed, the frequency component α2 does not reach a predetermined level. Therefore, the channel determination circuit 63R does not control the channel switching circuit 53.

Thus, the switch s1 is connected to the individual contact s
1L, and outputs the output signal of the low-pass filter 52L from the output terminal 71L of the left channel. As a result, the audio signal of the left channel is transmitted to the amplifier 6L and the speaker 7L.
Sounded by The switch s2 conducts to the individual contact s2R, and outputs the output signal of the low-pass filter 52R from the output terminal 71R of the right channel. As a result, the audio signal of the right channel is acousticized by the amplifier 6R and the speaker 7R.

On the other hand, when the transmission lines 4L and 4R are switched, the 1-bit digital signal of the left channel is supplied to the input terminal 4 for the right channel in the receiving circuit 5.
Input to 2R. As a result, the frequency α2 component of the 1-bit digital signal exceeds a predetermined level. Therefore, the channel determination circuit 63R for the right channel determines that channel information indicating the left channel is superimposed, and conversely to the case where the transmission paths 4L and 4R are correctly connected,
The switch s1 selects the individual contact s1R side, and the switch s2 selects the individual contact s2L side. As a result, even when the 1-bit digital signal of the left channel is erroneously input to the input terminal 42R for the right channel, the receiving circuit 5 converts the audio signal obtained by demodulating the 1-bit digital signal into the left channel. Output correctly from the output terminal 71L.

As described above, the receiving circuit 5 receives the received 1
When the channels of the bit digital signal have been switched, the left and right channels can be switched and output based on the channel information superimposed on the 1-bit digital signal.
As a result, even when a 1-bit digital signal of an unusual channel is transmitted to the receiving circuit 5 due to the exchange of the transmission lines 4R and 4L, the audio signal transmission apparatus 1 can transmit the audio signal of each channel. Can be sounded in the correct channel.

In the above configuration, since the sub signal is superimposed on the main signal by frequency division multiplexing, a special format or the like is used as in the conventional method of transmitting the main signal and the sub signal by time division multiplexing. No error prevention circuit is required. Since the signal is superimposed by frequency division multiplexing, the adder 13 in the delta-sigma modulation circuit 31
(See FIG. 1). As a result, the configuration for transmitting the sub-signal can be greatly simplified, and the main signal and the sub-signal can be transmitted without impairing the advantages of the 1-bit digital encoding method.

In the above description, the case where channel information is superimposed only on the 1-bit digital signal of the left channel has been described. However, the present invention is not limited to this. For example, the channel information may be superimposed only on the right channel. Further, for example, in the case of the right channel, a flag is set for the zero frequency α1, and in the case of the left channel, a flag is set for the zero frequency α2, and different channel information is superimposed on each of the 1-bit digital signals of both channels. You may. If channel information is superimposed on at least one 1-bit digital signal of the 1-bit digital signals of each channel, the same effect as in the present embodiment can be obtained.

In the above description, the case of two channels on the left and right has been described. However, the present invention is not limited to this.
The present invention is also applicable to a case where the audio signal transmission device 1 includes a plurality of channels. For example, the present invention can also be applied to a case where a receiving circuit separates a multi-channel including three front channels (right, center, and left) and two rear channels (right and left) and identifies each channel by a receiving circuit. In this case, as an example of the correspondence between the channel information and the zero-point frequency, in the case of the front right channel, only the zero-point frequency α1 is set, and in the case of the front left channel, only the zero-point frequency α2 is set. , For the front center channel, the zero point frequency α3
Only flag. Further, in the case of the rear right channel, a flag is set for both the zero point frequencies α1 and α2, and in the case of the rear left channel, a flag is set for both the zero point frequencies α1 and α3. As described above, the combination of the zero-point frequencies can support channels equal to or more than the number of zero-point frequencies.

[Second Embodiment] In the first embodiment described above, the case where channel information is superimposed as a sub signal has been described. On the other hand, in the present embodiment, a case will be described with reference to FIG. 5 where when the audio signal transmission device 1a transmits an audio signal serving as a main signal, a flag indicating the presence or absence of pre-emphasis is superimposed as a sub signal. . The pre-emphasis means a process of emphasizing a predetermined frequency component in advance on the audio signal input to the delta-sigma modulation circuit 31. If the pre-emphasis has been performed, the reception of the audio signal transmission device 1a The circuit 5a performs a process of lowering the level of the predetermined frequency component when demodulating the audio signal, that is, performs a de-emphasis process. Thereby, the receiving circuit 5a can return the frequency characteristic of the analog audio signal output to the amplifiers 6L and 6R to flat.

The pre-emphasis process is a process for emphasizing a predetermined frequency component. For example, the pre-emphasis process emphasizes a high-frequency component and suppresses a low-frequency component. To emphasize high-frequency components,
Various frequency components may be emphasized. In the following, as an example, by pre-emphasis processing,
A case where the high frequency component is emphasized will be described.

More specifically, in the audio signal transmission apparatus 1a according to the present embodiment, de-emphasis circuits 54L and 54R are provided in the receiving circuit 5a instead of the channel switching circuit 53 shown in FIG. An emphasis determination circuit 64L is provided instead of the channel determination circuit 63L. In the receiving circuit 5a according to the present embodiment, the emphasis determining circuit 64L is provided only for the left channel, and the emphasis determining circuit 64L controls the de-emphasis circuits 54L and 54R of both channels. Accordingly, in the receiving circuit 5a, the band pass filter 62R and the channel discriminating circuit 63R for the right channel are omitted from the receiving circuit 5 shown in FIG. The de-emphasis circuit 54 and the emphasis determination circuit 6
Reference numeral 4 corresponds to the control means described in the claims.

In transmitting circuit 3a, additional information signal generating circuit 21 for generating an emphasis determining signal is used instead of additional information signal generating circuit 21 for generating a channel determining signal.
a is provided. For convenience of explanation, members having the same functions as those described in the drawings of the above-described first embodiment are denoted by the same reference numerals, and description thereof is omitted.

The additional information signal generating circuit 21a comprises an oscillator 22 and a switch 23, like the additional information signal generating circuit 21. However, in this embodiment, the switch 23 conducts when the analog audio signal input to the delta-sigma modulation circuit 31 is pre-emphasized, and when the pre-emphasis is not performed,
Will be shut off. Note that, when a pre-emphasis circuit is provided in the transmission circuit 3, the opening and closing of the switch 23 is performed in conjunction with the off / on of the pre-emphasis circuit. When a pre-emphasis circuit is provided on the side of the audio signal sources 2L and 2R, a dedicated switching signal is transmitted from the audio signal sources 2L and 2R to the transmission circuit 3a, and based on the switching signal. , The opening and closing of the switch 23 may be controlled. Further, the switch 23 may be opened and closed based on a user's designation. In any case, when pre-emphasis is performed, a pre-emphasis determination signal is applied to the delta-sigma modulation circuit 31 via the switch 23.

In this embodiment, the oscillation frequency of the oscillator 22 is set to α1. Therefore, when the pre-emphasis is on, the 1-bit digital signal output from the output terminal 41L of the left channel by the transmission circuit 3a includes:
As the sub signal, a flag is set at the zero frequency α1.

On the other hand, the left channel de-emphasis circuit 54L provided in the receiving circuit 5a includes resistors r1L and r2L provided between the low-pass filter 52L and the output terminal 71L and connected in series with each other. r1L
A capacitor cL having one end connected to r2L and a switch s3L for selecting whether to ground the other end of the capacitor cL are provided. Similarly, the right channel de-emphasis circuit 54R includes resistors r1R and r2R, a capacitor cR, and a switch s3R. As will be described later, when performing de-emphasis, the switches s3L and s3R are turned on in response to an instruction from the emphasis determination circuit 64. As a result, a low-pass filter is formed, and both de-emphasis circuits 54L / 5
The 4R attenuation can be increased as the frequency increases. In each de-emphasis circuit 54, the size of the resistors R1 and R2 and the size of the capacitor C are
The size is set in advance so that the pre-emphasis processing can be canceled.

Therefore, both de-emphasis circuits 54
L · 54R suppresses high frequency components in the output signals of both low-pass filters 52L / 52R, and
・ Output from 71R. Thereby, when the high frequency component is emphasized in the pre-emphasis processing, the receiving circuit 5a cancels the pre-emphasis processing and converts the analog audio signal having a flat frequency characteristic into the amplifiers 6L and 6L.
Can be output to R.

The de-emphasis circuit 54 is configured in accordance with the constant of the pre-emphasis. For example, when the pre-emphasis processing is for emphasizing low frequencies, a high-pass filter is formed when the switch s3 is turned on. You.

The emphasis determination circuit 64 is provided in the
In the same way as the channel discriminating circuit 63 shown in (1), an emphasis discriminating signal, which is a sub signal, is extracted from the output signal of each demodulating circuit 51, and each of the de-emphasis circuits 54 is controlled. Specifically, when the zero-point frequency α1 component exceeds a predetermined level in the output signal of the demodulation circuit 51, the de-emphasis circuit 54 determines that the audio signal as the main signal is pre-emphasized, and Switch s3L
-Make s3R conductive.

As described above, in the audio signal transmission apparatus 1a having the above configuration, the transmission circuit 3a can superimpose the sub-signal indicating the presence or absence of pre-emphasis closely related to the audio signal on the 1-bit digital signal and transmit it. The receiving circuit 5
“a” can automatically select on / off of de-emphasis based on the sub-signal. Furthermore, just connect the emphasis determination signal to the light emitting diode as it is,
A display circuit that indicates the presence or absence of pre-emphasis can be configured.

[Third Embodiment] As still another embodiment of the present invention, in this embodiment, a case where the time information of the audio signal serving as the main signal is added as a sub signal will be described with reference to FIG. I do. Note that the audio signal transmission device 1b according to the present embodiment is similar to the audio signal transmission device 1 according to the first embodiment, and therefore, for convenience of explanation, members described in the drawings of the above-described first embodiment. Members having the same functions as those described above are denoted by the same reference numerals, and description thereof will be omitted.

In the audio signal transmitting apparatus 1b according to the present embodiment, an additional information signal generating circuit 21b for generating a time information signal is provided in the transmitting circuit 3b instead of the additional information signal generating circuit 21 shown in FIG. I have. The time information is information indicating the total time when transmitting the audio signal, or, for example, when the audio signal is divided into a plurality of parts, such as a song, information indicating the elapsed time for each song, and the like, 8
It has about a bit of information. Note that this time information is transmitted to the transmission circuit 3 similarly to the above-described emphasis determination signal.
b, or may be input from the audio signal source 2 side.

More specifically, the additional information signal generating circuit 21b includes an oscillator 22 for generating sine waves of each of the zero-point frequencies α1 to α3, and a time information generating circuit 24 for generating a digital signal corresponding to time information. And an encoder 2 for amplitude-modulating each of the sine waves based on the digital signal.
5 is provided. The encoder 25 converts the digital signal from the time information generation circuit 24 into each of the zero point frequencies α1 to α1.
It is divided into bit strings corresponding to α3. In this embodiment,
The time information is about 8 bits, and the zero frequency is set to three. Therefore, the time information is divided into three bit strings having a length of 3 bits. Further, the encoder 25
Converts the sine wave of each zero point frequency input from the oscillator 22 into 8 bits according to the value of the bit string corresponding to each zero point frequency.
Amplitude modulation is performed in stages. Also, the encoder 25 generates a time information signal by superimposing the amplitude-modulated signals.
Thereby, the additional information signal generation circuit 21b can apply the time information signal to the delta-sigma modulation circuit 31 as the additional information signal.

On the other hand, in the receiving circuit 5b, a decoder (control means) 65 for demodulating the time information signal and a display device 67 in accordance with an instruction from the decoder 65 are provided in place of the channel discriminating circuit 63L shown in FIG. Display drive circuit 66 to be driven
Are provided. In the receiving circuit 5b, the band pass filter 62 and the channel discriminating circuit 63 on the right channel side and the channel switching circuit 53 are omitted from the receiving circuit 5 shown in FIG. 2, and the outputs of the low-pass filters 52L and 52R are omitted. The signal is output directly from the output terminal 71L.
・ Output from 71R.

The decoder 65 receives the output signal of the demodulation circuit 51 via the band-pass filter 62, and extracts the frequency components of the zero-point frequencies α1 to α3 by using Fourier transform. Further, the decoder 65 demodulates into a digital signal indicating time information in a procedure reverse to that of the encoder 25. Specifically, the decoder 65 amplitude-demodulates each frequency component to generate a 3-bit bit string, and outputs a digital signal indicating time information by concatenating each bit string.

The display device 67 is configured by, for example, arranging a plurality of date character segments. Each segment can be turned on / off for each node of the character "day" based on the instruction of the display drive circuit 66, and can display a number or an alphabetic character. The display drive circuit 66 includes a decoder 65
The lighting node of each segment is determined on the basis of the digital signal from, and the display of the display device 67 is controlled by, for example, applying a voltage to a terminal indicating the lighting node of each segment. Thus, the display device 67 can display a character string indicating the time information.

Note that, at each of the zero-point frequencies α1 to α3,
When the necessary range for amplitude modulation in eight stages cannot be secured as the dynamic range of the sub-signal, one word may be formed by combining several flags that are sequentially superimposed and expressing time information in word units. For example, when only one bit, that is, a range in which amplitude modulation can be performed in two steps, can be secured as the dynamic range of the sub signal, the encoder 25
Divides the digital signal from the time information generating circuit 24 into three bits, and interrupts the sine wave from the oscillator 22 at a predetermined cycle according to the value of each bit. As a result, at each zero-point frequency, time information can be transmitted even when the total range that can be secured as the dynamic range of the sub-signal is less than the size required for transmitting time information.

[Fourth Embodiment] As still another embodiment of the present invention, in the present embodiment, when transmitting an audio signal to be a main signal, it is used as a sub signal to protect the copyright of the audio signal. The case where the flag is superimposed and transmitted will be described with reference to FIG. Note that the audio signal transmission device 1c according to the present embodiment is also similar to the audio signal transmission device 1 according to the first embodiment, and therefore, for convenience of explanation, the members described in the drawings of the above-described first embodiment. Members having the same functions as those described above are denoted by the same reference numerals, and description thereof will be omitted.

In the audio signal transmitting apparatus 1c according to the present embodiment, the transmitting circuit 3c generates a flag signal indicating the presence or absence of a flag for copyright protection in place of the additional information signal generating circuit 21 shown in FIG. Additional information signal generation circuit 21
c is provided. On the other hand, the receiving circuit 5c is provided with an output control circuit 55 for selecting whether or not to output an audio signal, instead of the channel switching circuit 53 shown in FIG. 2, and instead of the channel discriminating circuits 63L and 63R. And flag determination circuits 68L and 68R for determining the flag signals. Note that the output control circuit 55 and the flag determination circuit 68 correspond to the control means described in the claims.

The flag is added to control the copying and duplication of the audio signal serving as the main signal. In this embodiment, when the audio signal is copied once,
That is, when signal transmission from the transmission circuit 3c to the reception circuit 5c is performed once, the transmission circuit 3c superimposes a flag signal indicating presence of a flag on a 1-bit digital signal and transmits the signal.
On the other hand, when the flag signal indicates that the flag is present, the receiving circuit 5c blocks the demodulated output, that is, the reproduction of the 1-bit digital signal.

More specifically, the additional information signal generation circuit 2
1c, the oscillator 22 has, for example, a zero-point frequency α1
For example, a sine wave having a predetermined zero-point frequency is continuously output.
The switch 23 conducts when the audio signal is copied once, and applies the sine wave to the delta-sigma modulation circuit 31 as a flag signal. As a result, when the audio signal is copied once, a flag signal indicating that a flag is present is superimposed on the audio signal and delta-sigma modulated to a 1-bit digital signal.

In the receiving circuit 5c, the output control circuit 55 includes a switch s4L provided between the low-pass filter 52L and the output terminal 71L, and a switch s4 provided between the low-pass filter 52R and the output terminal 71R.
4R. Further, each flag discriminating circuit 68
Has the same configuration as the channel determination circuit 63 shown in FIG. 2, and determines the presence or absence of a flag based on the magnitude of the zero-point frequency α1 component in the output signal of the demodulation circuit 51, and opens and closes the switches s4L and s4R. Control. Specifically, each flag determination circuit 68 determines that there is a flag when the frequency component exceeds a predetermined level. When at least one of the switches s4L and s4R is determined to have a flag, the flag determination circuit 68 shuts off the switches s4L and s4R.
When both the flag determination circuits 68 determine that there is no flag, the switches s4L and s4R are turned on.

For example, when a 1-bit digital signal is directly applied to a receiving circuit 5c from an audio signal source (not shown), a flag signal indicating that a flag is present is superimposed on the 1-bit digital signal input to the receiving circuit 5c. If not, the flag determination circuit 68 determines that both switches s4L · s
Conduct 4R. As a result, the 1-bit digital signal is supplied to the demodulation circuit 51, the low-pass filter 52, and
Via the output control circuit 55, as an analog audio signal,
Output from output terminals 7L and 7R.

On the other hand, as shown in FIG. 7, when the audio signal output from the audio signal source 2 is transmitted to the receiving circuit 5c via the transmitting circuit 3c and the transmission path 4, the transmitting circuit 3c A flag signal indicating the presence of a flag is transmitted by being superimposed on a 1-bit digital signal. Therefore, the receiving circuit 5c
Then, the flag discrimination circuit 68 determines that both switches s4L · s
Block 4R. Thereby, the low-pass filter 5
The output signal of No. 2 is blocked from being transmitted by the output control circuit 55, and is not output from the output terminals 7L and 7R. As a result,
According to the intention of the creator of the audio signal, the copying or the number of times of copying of the audio signal can be controlled, and the copyright of the creator of the audio signal can be protected.

Here, the carrier frequency of the flag signal is
It is set to the zero point frequency and is within the effective frequency band of the audio signal that is the main signal. Therefore, it is extremely difficult for a third party who does not know the zero point frequency to falsify the flag signal from the 1-bit digital signal transmitted on the transmission path 4. For example, in the case of the multi-bit encoding method, since the bit indicating the audio signal and the bit indicating the flag signal are transmitted by time division multiplexing, all bits are received from the digital signal passing through the transmission path 4, By falsifying bits in a predetermined order, the flag signal can be falsified. Also,
As in the present embodiment, even when the audio signal and the flag signal are transmitted by frequency division multiplexing, if the frequency band of the audio signal and the frequency band of the flag signal are different,
For example, if a band-pass filter that passes only the frequency band of the audio signal is used, only the audio signal can be extracted from the 1-bit digital signal that passes through the transmission path 4. On the other hand, in the present embodiment, since the frequency band of the flag signal and the frequency band of the audio signal overlap, it is extremely difficult to separate the two. For example, even if only the frequency band component of the audio signal is extracted from the 1-bit digital signal,
The extracted signal includes a flag signal. As a result, falsification of the flag signal by a third party can be prevented, and the copyright of the creator of the audio signal can be more reliably defended than in the related art.

In the present embodiment, the flag signal only distinguishes the presence or absence of the flag, and the receiving circuit 5c determines only whether or not the audio signal has been copied.
It is not limited to this. If a signal indicating the number of times that the receiving circuit 5c can copy is used as the flag signal, the number of times the audio signal is copied can be limited to the number intended by the creator of the audio signal. Specifically, the audio signal source 2 superimposes a flag signal indicating the number of copies intended by the creator of the audio signal in advance on the output audio signal via a carrier having a predetermined zero frequency by frequency division multiplexing. Additional information signal generation circuit 21c
Generates a flag signal indicating the number of times one less than the number of times indicated by the flag signal, and generates a delta-sigma modulation circuit 31
Modulates the audio signal after removing the superimposed flag signal into a 1-bit digital signal, and superimposes a new flag signal generated by the additional information signal generation circuit 21c on the 1-bit digital signal. Further, the receiving circuit 5
The flag discriminating circuit 68 of c identifies the number of times indicated by the flag signal, and causes the output control circuit 55 to output the demodulated audio signal only when the number of times is greater than 0.

[Fifth Embodiment] As still another embodiment of the present invention, in this embodiment, when transmitting an audio signal serving as a main signal, the ID of the audio signal is used as a sub signal.
A case in which a code is superimposed and transmitted will be described with reference to FIG. Note that the audio signal transmission device 1 according to the present embodiment
d is the audio signal transmission device 1c according to the fourth embodiment.
Therefore, for convenience of explanation, members having the same functions as those described in the drawings of the above-described fourth embodiment are denoted by the same reference numerals, and description thereof is omitted.

In the audio signal transmitting apparatus 1d according to this embodiment, the transmitting circuit 3d replaces the additional information signal generating circuit 21c shown in FIG. 7 with the additional information signal generating circuit 21d for generating a code signal indicating the ID code. Is provided. Similarly, in the receiving circuit 5d, instead of the flag determining circuits 68L and 68R shown in FIG. 7, code determining circuits (control means) 69L and 69R for determining the code signal and controlling the output control circuit 55 are provided. Have been.

The ID code is a code for identifying the audio signal itself as a main signal, and the receiving circuit 5d
Based on the ID code added by the transmission circuit 3d, the audio signal that can be enjoyed by itself is determined to suppress copying and copying. Using this ID code, for example, by using a wireless or wired or recording medium, an audio signal on which the ID code is superimposed is distributed to a plurality of audiences, and among those audiences, only those who have paid a predetermined fee, An audio signal transmission device 1d that can reproduce the audio signal can be realized.

In the present embodiment, as an example of encoding an ID code, the ID code is represented by a binary number, and a zero-point frequency is assigned to each digit of the binary number. Further, when a certain digit is “1”, a flag is set for the zero frequency corresponding to the digit, and when the digit is “0”, no flag is set. For example, if the zero-point frequency α1 is assigned to the first digit, α2 is assigned to the second digit, and α3 is assigned to the third digit, the ID code “101” becomes α1 and α3
And a flag, and the ID code "011"
Is expressed by setting flags for α2 and α3.

In this case, the additional information signal generating circuit 2
In 1d, the oscillator 22 outputs sine waves of three zero-point frequencies α1 to α3, respectively, and the switch 23 provided in association with each sine wave conducts when a flag is set at a corresponding frequency, and the flag is set. It will be cut off if you can not stand. As a result, the additional information signal generation circuit 21d
Outputs a code signal indicating a code. The code signal is superimposed on the main audio signal by the delta-sigma modulation circuit 31.

On the other hand, the code discriminating circuit 69 includes the demodulating circuit 5
Each zero-point frequency component is extracted from one output signal to identify an ID code superimposed on the one-bit digital signal. When the ID code satisfies a predetermined condition, both switches s4L and s4R of the output control circuit 55 are turned on. Otherwise, both switches s4L and s4L.
Block 4R. The predetermined condition is, for example, whether the ID code matches the ID code stored in the code determination circuit 69 in advance, or whether the calculation result using the ID code is within a certain range. Various settings can be made according to the purpose of use.

As a result, the receiving circuit 5d receives the received 1
The audio signal can be output from each output terminal 71 only when the ID code superimposed on the bit digital signal is an acceptable ID code.

In the present embodiment, the case where the ID code of the audio signal is added as the sub-signal has been described. However, the same effect can be obtained when a mastering code is added instead of the ID code. Specifically, when recording a master audio signal, for example, a flag is set to a zero-point frequency α1 as a code signal indicating that the audio signal is a master. The delta-sigma modulation circuit 31 superimposes the code signal on a 1-bit digital signal, and the 1-bit digital signal is written on the recording medium. On the other hand, the code discriminating circuit 69 of the receiving circuit 5d
Controls the output control circuit 55 in response to the code signal superimposed on the 1-bit digital signal when reproducing the 1-bit digital signal from the recording medium. Accordingly, when the mastering code is not added, the receiving circuit 5d suppresses the copying and duplication of the audio signal, for example, by suppressing the output of the audio signal.

Note that the sub-signals superimposed in the first to fifth embodiments are merely examples, and how the sub-signals are coded, or how many bits of information amount correspond to which zero-point frequency. Whether to assign a flag having is set in various ways. However, the level of the additional information signal superimposed at a certain zero frequency is smaller than the noise level at the zero frequency to the lower limit of the audio signal level.
Must be set small. Therefore, the information amount of the flag added to one zero frequency is limited by the noise level in the dip and the dynamic range of the audio signal. Further, as shown in FIGS. 9 to 11, by setting the number of zero-point frequencies to a plurality and combining flags added to each zero-point frequency, various types of sub-signals can be multiplexed.

In addition, by combining several flags that are sequentially superimposed to form one word and expressing sub-signals in word units, more sub-signals can be superimposed. However, in this case, word synchronization is required for the transmission of the sub-signal, similarly to the case where the main signal is transmitted using the multi-bit encoding method as in the related art. Therefore, as compared with a case where the sub-signal is not transmitted by time division multiplexing, the circuit becomes complicated and it becomes difficult to change the standard. However, unlike the conventional case, the main signal is transmitted using a 1-bit digital signal even when the sub-signal is transmitted by the multi-bit encoding method.
Therefore, the separation of the sub-signal from the main signal and the processing of the main signal can be realized by the same circuit as when the sub-signal is not transmitted by time division multiplexing. Therefore, similar to the above embodiments, the sub-signal can be superimposed on the main signal without complicating the main signal processing circuit. In order to extract the sub-signal, it is necessary to separate the sub-signal from the main signal before synchronizing the words. Similarly, it is difficult to falsify the sub-signal because it is within the band.

In each of the first to fifth embodiments, the case where one type of sub-signal is added has been described. However, the present invention is not limited to this, and a plurality of types of sub-signals may be superimposed on the main signal. . For example, each of the emphasis determination signal and the above-described channel determination signal is a signal having an information amount of 1 bit, and can be transmitted at one zero frequency. Therefore, for example, when the pre-emphasis processing is performed, the emphasis determination signal is superimposed on the carrier frequency of the zero frequency α1 shown in FIG.
The channel discrimination signal can be superimposed at the carrier frequency of the zero frequency α2. As described above, by setting the carrier frequency of the emphasis determination signal and the carrier frequency of the channel determination signal to different zero-point frequencies, the flag indicating the presence or absence of pre-emphasis and the channel information for the audio signal serving as the main signal are set. Are simultaneously superimposed and transmitted by frequency division multiplexing.

Further, in each of the above-described embodiments, for example, a case where a 1-bit digital signal is transmitted via the transmission path 4 such as an optical fiber has been described. However, the present invention is not limited to this. The present invention provides, for example, the transmission circuit 3 (3a to 3a).
d) is also applicable when the 1-bit digital signal is recorded on a recording medium, and the receiving circuit 5 (5a to 5d) reproduces the 1-bit digital signal from the recording medium. Receiving circuit 5
If (5a to 5d) receives the 1-bit digital signal output from the transmission circuit 3 (3a to 3d), the same effects as in the above embodiments can be obtained.

Further, in each of the above embodiments, the case where the audio signal is transmitted as the main signal has been described. However, the present invention is not limited to this. Signal
It can be applied to the case of transmitting other signals.

[0129]

According to the first aspect of the present invention, as described above, the signal transmission method using the 1-bit digital signal includes the step of transmitting the main signal via the 1-bit digital signal within the effective frequency band. And a step of superimposing a sub-signal on the main signal of the 1-bit digital signal by frequency division multiplexing at a specific frequency at which quantization noise is reduced by the zero point control; Extracting the sub-signal by discriminating the specific frequency of the bit digital signal.

In the above configuration, at the specific frequency,
Since the level of quantization noise is reduced, both the dynamic range of the main signal and the dynamic range of the sub signal can be easily secured, and the sub signal can be superimposed on the main signal by frequency division multiplexing. As a result, for example, there is an effect that the main signal and the sub-signal can be superimposed without obstructing the advantage of transmitting a signal as a 1-bit digital signal, such as simplification of a demodulation circuit.

The specific frequency is set within the effective frequency band of the main signal. Therefore, a third party who does not know the specific frequency cannot separate the main signal and the sub signal. As a result, there is an effect that the alteration of the sub signal by a third party can be reliably prevented.

The delta-sigma modulation circuit according to the second aspect of the present invention includes the sub-signal superimposing means for superimposing the sub-signal on the main signal of the 1-bit digital signal by frequency division multiplexing at a specific frequency. Configuration.

Therefore, a delta-sigma modulation circuit capable of modulating a main signal and a sub-signal into a 1-bit digital signal without obstructing the feature of the delta-sigma modulation that demodulation is easy as in claim 1 is provided. It has the effect that it can be provided. In addition, there is an effect that it is difficult to remove or falsify the sub-signal by a third party.

As described above, in the delta-sigma modulation circuit according to the third aspect of the present invention, in the configuration of the second aspect, the sub-signal superimposing means includes the sub-signal superimposing means provided to one of the inputs of the adder. In this configuration, a signal is input via a carrier having the specific frequency.

In the above configuration, since the adder used for delta-sigma modulation is also used for superimposing the sub-signal, the circuit provided for superimposition can be simplified.

As described above, in the delta-sigma modulation circuit according to the fourth aspect of the present invention, in the configuration of the second or third aspect, the main signal is an audio signal, and the sub-signal is channel information. , Pre-emphasis, copyright protection flag, ID code, mastering code, or time information.

In the above configuration, each sub-signal indicates information that is closely related to the main audio signal and has a small amount of information. Therefore, even if the dynamic range of the sub-signal at the specific frequency cannot be made very wide, the delta-sigma modulation circuit can superimpose and transmit or record the sub-signal with a sufficient S / N. As a result, on the demodulation side, there is an effect that processing related to the main signal can be performed based on the sub signal.

In the demodulation circuit according to the fifth aspect of the present invention, as described above, the main signal of the 1-bit digital signal generated by using the zero point control is such that the sub signal is a carrier wave of a specific frequency corresponding to the zero point control. And a control unit that discriminates the specific frequency component from the 1-bit digital signal to extract the sub-signal and performs predetermined processing according to the sub-signal. Configuration.

In the above configuration, since the level of the quantization noise of the 1-bit digital signal is reduced at a specific frequency within the frequency band of the main signal, the S / N of the sub signal can be sufficiently ensured. Therefore, the control unit has an effect that the sub-signal superimposed on the 1-bit digital signal can be extracted with a simple configuration. Further, since the sub-signals are superimposed by frequency division multiplexing, the demodulation circuit also has an effect that the main signal can be easily demodulated as compared with the case where the sub-signals are superimposed by time division multiplexing.

According to a sixth aspect of the present invention, in the demodulation circuit according to the fifth aspect of the present invention, the main signal is an audio signal, and the sub-signal is a channel of the audio signal. In addition to the channel information shown, the control means performs left / right or multi-channel separation based on the channel information.

Therefore, the demodulation circuit can correctly determine the channel of the audio signal, and even if an audio signal of a channel different from the normal channel is input due to switching of the transmission path or the like, the demodulation circuit can use the correct channel for the audio signal. This has the effect of being able to output.

According to a seventh aspect of the present invention, in the demodulation circuit according to the fifth aspect of the present invention, the main signal is an audio signal, and the sub signal is a pre-emphasis of the audio signal. The control means controls on / off of de-emphasis based on the flag.

Therefore, the demodulation circuit can reliably determine whether the received 1-bit digital audio signal is a signal that has been subjected to pre-emphasis processing and apply de-emphasis to the audio signal. To play.

As described above, in the demodulation circuit according to the eighth aspect of the present invention, in the configuration of the fifth aspect, the main signal is an audio signal, and the sub-signal is a copyright of the audio signal. The control means is configured to limit copying or demodulation output of the audio signal based on at least one of a flag for protection, an ID code, and a mastering code, based on the sub-signal.

In the above arrangement, the control means extracts a sub-signal from the 1-bit digital signal, and limits the copying or demodulation output of the audio signal when the sub-signal does not permit copying or demodulation output. As a result, there is an effect that the modulation side can specify whether to permit copying or demodulation output on the demodulation side.

Further, since the sub-signal is frequency-division multiplexed at a specific frequency within the effective frequency band of the audio signal, it is difficult to falsify the sub-signal. As a result, the demodulation circuit has an effect that the copying or demodulation output of the audio signal can be reliably restricted based on the permission / non-permission of the copying or demodulation output instructed on the modulation side.

[Brief description of the drawings]

FIG. 1 illustrates one embodiment of the present invention, and is a block diagram illustrating a main configuration of a delta-sigma modulation circuit.

FIG. 2 is a block diagram showing the overall configuration of the audio signal transmission device when the delta-sigma modulation circuit superimposes channel information as a sub-signal.

FIG. 3 is a graph showing a frequency characteristic of a quantization noise level in a 1-bit digital signal output by the delta-sigma modulation circuit.

FIG. 4 is a block diagram showing a delta-sigma modulation circuit on a side on which a sub signal is not superimposed in the audio signal transmission device.

FIG. 5, showing another embodiment of the present invention, is a block diagram illustrating an audio signal transmission device that adds the presence or absence of pre-emphasis as a sub signal.

FIG. 6 shows still another embodiment of the present invention, and is a block diagram illustrating an audio signal transmission device that adds time information as a sub signal.

FIG. 7 shows still another embodiment of the present invention, and is a block diagram illustrating an audio signal transmission device that adds a flag for copyright protection as a sub signal.

FIG. 8 shows still another embodiment of the present invention, and is a block diagram illustrating an audio signal transmission device that adds an ID code as a sub signal.

FIG. 9 is a graph for explaining the relationship between the frequency characteristic of the quantization noise level and a sub signal.

FIG. 10 is a graph for explaining the relationship between the frequency characteristic of the quantization noise level and a sub signal.

FIG. 11 is a graph for explaining the relationship between the frequency characteristic of the quantization noise level and a sub signal.

FIG. 12 shows a conventional example, and is a block diagram showing a main configuration of a delta-sigma modulation circuit.

FIG. 13 is a graph showing a frequency characteristic of a quantization noise level in a conventional multi-bit encoding method.

[Explanation of symbols]

4L / 4R transmission line 5.5a-5d receiving circuit (demodulation circuit) 13 adder 14 quantizer m1-m7 integrator m11-m13 feedback circuit (partial negative feedback circuit) 31 delta-sigma modulation circuit 21-21a-21d addition Information signal generating circuit (sub-signal superimposing means) 53 Channel switching circuit (control means) 54L / 54R de-emphasis circuit (control means) 55 Output control circuit (control means) 63L / 63R Channel discriminating circuit (control means) 64L emphasis discriminating circuit (Control means) 65 Decoder (Control means) 68L / 68R Flag discriminating circuit (Control means) 69L / 69R Code discriminating circuit (Control means)

Claims (8)

[Claims] A main signal having a predetermined effective frequency is subjected to delta sigma modulation using a zero point control so that quantization noise at a predetermined specific frequency within the effective frequency band is reduced to a 1-bit digital signal. A signal transmission method via a 1-bit digital signal, comprising: a modulation step; a transmission step of transmitting a 1-bit digital signal via a transmission path or a recording medium; and a step of demodulating the transmitted 1-bit digital signal. Further, before the transmitting step, a sub-signal is superimposed on the main signal of the 1-bit digital signal by frequency division multiplexing at the specific frequency, and after the transmitting step, Extracting the sub-signal by discriminating the specific frequency. A method for transmitting a signal via a 1-bit digital signal. 2. An input signal serving as a main signal is input to a first stage,
A plurality of integrators connected in cascade with each other, an adder for adding the outputs of the respective integrators, a quantizer for quantizing the output of the adder and outputting a 1-bit digital signal, and the integrator A negative feedback circuit for negatively feeding back the output of the integrator to the input side of the integrator preceding the integrator to reduce the quantization noise of the 1-bit digital signal at a predetermined specific frequency. 3. The delta-sigma modulation circuit according to claim 1, further comprising a sub-signal superimposing unit configured to superimpose a sub-signal on the main signal of the 1-bit digital signal by frequency division multiplexing at the specific frequency. 3. The delta-sigma modulation circuit according to claim 2, wherein the sub-signal superimposing means inputs the sub-signal to one of the inputs of the adder via a carrier having the specific frequency. . 4. The main signal is an audio signal, and the sub-signal is at least one of channel information, presence / absence of pre-emphasis, a flag for copyright protection, an ID code, a mastering code, and time information. 4. The delta-sigma modulation circuit according to claim 2, wherein the signal is a signal indicating one. 5. A main signal having a predetermined effective frequency band,
A demodulation circuit for demodulating a 1-bit digital signal generated by delta-sigma modulation so as to reduce quantization noise at a predetermined specific frequency within the effective frequency band using zero point control, In the main signal, a sub-signal is superimposed by frequency division multiplexing via a carrier of the specific frequency, and the sub-signal is extracted by discriminating the specific frequency component from the 1-bit digital signal, and A demodulation circuit characterized by comprising control means for performing a predetermined process according to the following. 6. The main signal is an audio signal, the sub-signal is channel information indicating a channel of the audio signal, and the control means is configured to control left and right or multi-channel based on the channel information. The demodulation circuit according to claim 5, wherein separation is performed. 7. The main signal is an audio signal, the sub-signal is a flag indicating the presence or absence of pre-emphasis of the audio signal, and the control means turns on / off the de-emphasis based on the flag. 6. The method according to claim 5, wherein the on / off is controlled.
A demodulation circuit as described. 8. The main signal is an audio signal, and the sub signal is a flag for protecting the copyright of the audio signal,
6. The demodulation circuit according to claim 5, wherein the control means limits copying or demodulation output of the audio signal based on the sub signal and at least one of a code and a mastering code. .