JPS5921144A - Signal transmitting system and its device - Google Patents

Abstract

PURPOSE:To reduce the equalizing noise down to about the minimum level, by applying A/D conversion to both audio and control signals at the transmitting side to synthesize both signals for transmission and then giving a D/A conversion to the received signals after separating them into data and control signals at the receiving side. CONSTITUTION:In a transmitting device, an output signal of a variable gain amplifier 11 is applied with A/D conversion 14 by a comparatively small number of bits, then with another A/D conversion 15 by further less number of bits. These converted signals are synthesized 16 and transmitted to a transmission system with application of a desired signal process. While a receiving device discriminates and separates the received data into a main data and a control information data through a signal process separating circuit 17. Then the main data and the control information data are given to a variable gain amplifier 21 after supplied with D/A conversion 18 and D/A conversion 19 respectively. The amplifier 21 is controlled variably in level to the output of the converter 18 in response to the output of a time constant circuit 20. Thus an audio signal in correct level is restored and delivered in low level noise through an output terminal A0.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention digitizes analog signals to create a transmission path,
The present invention relates to a signal transmission method that is applied to a transmission system such as a demodulation system or a recording/reproduction system, receives a transmission signal from the transmission system, and returns it to an analog signal, and a device directly used for implementing the method.

[Technical background of the invention]

Analog signals are digitized using PCM (pulse code modulation) and transmitted through a transmission system (in this case, "transmission" has a broad meaning that includes not only transmission through a transmission line but also through a modulation/demodulation system, recording/reproduction system, etc.) ), and when this is received and converted back into an analog signal, quantization noise occurs during PCM conversion of the analog signal. In order to reduce this quantization noise, it is generally believed that there is no suitable method other than increasing the number of bits of the digital signal during digitization in PCM conversion.

On the other hand, if the analog signal to be transmitted is an audio signal, for example, the conventional analog signal There is a method that applies the noise reduction method before and after the PCM transmission system.

That is, as shown in FIG. 1, the audio input applied to the input terminal A1 is encoded by the noise reduction encoder 1, and this encoded signal is converted to
After being digitized by the analog-to-digital converter 2 and subjected to necessary processing such as code error detection/correction processing and data compression in the transmitting side signal processing circuit 3, the transmission path,
It is sent to transmission systems such as modulation/demodulation systems and recording/reproduction systems. The PCM signal sent from the transmission system is subjected to processing such as code error correction processing and decompression/restoration processing of compressed data in the receiving side processing circuit 4, and is converted into an analog signal by the D/A (digital-to-analog) converter 5. The signal is then decoded by a noise reduction decoder 6 corresponding to the noise reduction encoder 3, and output as an audio output from an output terminal A0 for reproduction from a first speaker or the like.

In order to audibly reduce quantization noise, the analog signal input to the A/D converter 2 must be
It is preferable that the value is lower than the maximum value that can be handled by the A/
When input to the D converter 2, the signal is clipped and clipping distortion occurs. ). That is, A/D
It is desirable that the input signal of the converter 2 has a substantially constant value and a value that is less than or equal to the maximum value and sufficiently close to the maximum value.

On the other hand, when the conventional analog system noise reduction method is applied, the following problems occur.

(b) Although the principle of conventional general noise reduction methods reduces changes in signal level, in order to enable decoding, it is necessary to keep the analog output level on the encode side in a form that retains the amount of change. . In other words, in the conventional noise reduction method, the signal is transmitted (recorded, etc.) in such a way that it becomes louder than the noise generated in the transmission system such as the recording medium, but in this case, on the encode side, the large signal is left as is, and the small signal is Raise the level and restore the small signal on the decoding side. At this time, since the transmitted information is only a signal with a compressed dynamic range, decoding is performed based on the level of the transmitted signal. Therefore, even when increasing the level of a small signal during encoding, it must be made lower than the level of a large signal. Therefore, even when providing an encoded signal to the A/D converter, the input level of the A/D converter cannot be kept substantially constant. For these reasons, conventional noise reduction methods cannot sufficiently reduce the influence of quantization noise.

(b) Since the decoder side obtains control information based on the level of the encoded signal, that is, the signal input to the decoder, the control time constant must be large. This is because, for example, in the case of an audio signal, in order to obtain the correct signal level without causing ripples in the control signal even at the lower limit of the audible frequency, it is necessary to have a time constant of a sufficient value even at such low frequencies. The time constant on the encoder side is also determined accordingly. If the control time constant is large in this way, for example, in the case of a signal with a sudden attack such as the sound of a piano, the encoder side cannot control the signal in time, and an excessive level signal is applied to the A/D converter, causing clipping distortion.

(c) If clipping occurs on the encoder side or in the transmission system due to the cause of (b) above, the level relationship cannot be transmitted correctly, and not only will the clipped waveform be played back on the decoder side, but in many cases Even the parts that are not clipped will be out of level. This is due to the fact that the correct control voltage cannot be obtained on the decoder side due to the clipping phenomenon, which causes problems in sound quality such as piano attack.

[Purpose of the invention]

The present invention provides a transmission method and its implementation that can effectively reduce noise components such as quantization noise generated or mixed in a transmission path, etc. when transmitting a signal by digitizing an analog signal and returning it to the original analog signal. The purpose is to provide equipment for direct use.

[Summary of the invention]

The first invention according to the present invention is an invention of a "method", which converts an analog signal into a digital value and performs first level variable control so that the final digital value becomes a substantially constant value. 1 digital signal is obtained and the above first digital signal is obtained.
The control information in the level variable control of is a second digital signal consisting of a digital value having a smaller number of bits than the first digital signal, and these first and second digital signals are The synthesized signal is synthesized at a ratio of the number of data that is sufficiently small relative to the digital signal, and is given to the transmission system, and upon receiving this synthesized signal from the transmission system, the first and second digital signals are separated and extracted. The first digital signal is converted into an analog signal, and a second level variable control having substantially opposite characteristics to the first level variable control is performed based on the extracted second digital signal, thereby converting the first digital signal into an analog signal. This is a signal transmission method characterized by restoring the signal.

Further, a second invention according to the present invention is an invention of an "apparatus" directly used for carrying out the first invention, and includes an A/D conversion means for converting an analog signal into pre-converted digital data, and the A/D conversion means for converting an analog signal into pre-converted digital data. Performing digital (first) level variable control on the pre-converted digital data obtained by the D conversion means to produce a first digital signal having a smaller number of bits and a substantially constant level than the pre-converted digital data. level variable control means for obtaining a second digital signal having a smaller number of bits than the first digital signal from the control information in this (first) level variable control; The transmitting apparatus is characterized by comprising a signal synthesizing means for inserting the second digital signal at a sufficiently small rate between the data strings of the first digital signal and applying the second digital signal to the transmission system.

The third invention according to the present invention is an invention of a "device" directly used for carrying out the first invention, in which an analog signal is converted into a digital value and the final digital value is a substantially constant value. a first digital signal obtained by performing first level variable control such that a second digital signal consisting of a plurality of signals, and a second digital signal, which are synthesized at a rate such that the second digital signal is sufficiently smaller than the second digital signal, and which receives a transmission signal given to a transmission system and restores the original analog signal. a signal separation means for separately extracting the first and second digital signals from the received signal; and a signal separation means for separately extracting the first and second digital signals from the received signal; digitally using the digital signal as control information.
level variable control means for obtaining digital data having a greater number of bits than the first digital signal by performing second level variable control having characteristics substantially opposite to the level variable control; The receiving device is characterized in that it is equipped with a D/A conversion means for converting digital data into analog values.

[Embodiments of the invention]

FIG. 2 shows the configuration of an embodiment of the present invention.

In this embodiment, the audio input is level-variably controlled to a substantially constant level so that the signal level does not become too low, and A/D conversion is performed, and the control information in the level variable control is also A/D-converted separately. digital data,
The two types of data of the transmission signal are combined in a time-division manner and given to the transmission system at a rate such that one piece of control information data obtained by A/D converting the above control information is included in a plurality of data, and the receiving side receives the above two types of data of the transmission signal. The control information data is separated and D/A converted, and the other signal is level-variably controlled based on the D/A converted signal, so that the A/D conversion and D/A conversion are always optimal. This is done for signals at the signal level to reduce quantization noise and the like to a minimum level.

In FIG. 2, 11 is a variable gain amplifier for controlling the level of the audio signal input to the input terminal Ai, and 12 is a level detector consisting of a rectifier circuit using, for example, a diode, for detecting the output level of the variable gain amplifier 11. , 13 is a time constant circuit that gives a predetermined time constant to the rise and fall (so-called attack and release) of the output of the level detector 12 and supplies it to the variable gain amplifier 11 as a control signal.
4 is an A/D converter that A/D converts the output of the variable gain amplifier 11 to obtain main data; 15 is an A/D converter that converts the output of the time constant circuit 13, that is, the control signal supplied to the variable gain amplifier 11; An A/D converter 16 converts the outputs of the A/D converters 14 and 15 into control information data in a time-division manner as will be detailed later, and also performs signal processing for code error detection/correction, data compression processing, etc. This is a synthesis/signal processing circuit that performs the necessary signal processing and sends it to the transmission system, and these constitute the transmitting device. 17 is a signal processing/separation circuit that performs signal processing such as code error correction processing and decompression/restoration processing of compressed data on the transmission signal received from the transmission system, and separates the combined main data and control information data;
8 is a D/A converter that converts the main data separated and outputted by the signal processing/separation circuit 17 into D/A; 19 is a D/A converter that converts the control information data separated and outputted by the signal processing/separation circuit 17; A D/A converter, 20 is a time constant circuit that makes the output of the D/A converter 19 have a time constant corresponding to the time constant circuit 13 on the transmitting side, 21 is an output of the time constant circuit 20 for the output of the D/A converter 18; This is a variable gain amplifier that controls the level of the output signal of the D/A converter 19 to vary the level and outputs it as an audio signal from the output terminal A0 with control characteristics opposite to those of the variable gain amplifier 11 on the transmitting side. Configure.

Next, the operation in such a configuration will be explained.

The audio signal input to the input terminal Ai of the transmitter is controlled to a nearly constant signal level by the variable gain amplifier 11. That is, in this case, the variable gain amplifier 11 is
The level is detected by the level detector 12 by the feed pack circuit consisting of the detector 12 and the time constant circuit 13 (
Feedback is applied so that the output level (of the variable gain amplifier 11) remains approximately constant. The output signal of the variable gain amplifier 11 has a relatively small number of bits (compared to conventional systems, etc.), for example, an 8-bit A/D converter 14.
The control signal of the variable gain amplifier 11, that is, the output signal of the time constant circuit 13, is A/D converted by an A/D converter 15 with a smaller number of bits, for example, 4 bits.
D-converted. The digital data outputs of these A/D converters 14 and 15 are main data and control information data, respectively, and both of these data are synthesized in a synthesis/signal processing circuit 16, subjected to necessary signal processing, and sent to the transmission system. be done.

The most important point in this method is the synthesis/signal processing circuit 1
The main data and control information data are combined in step 6. That is, in this case, multiple pieces of main data are combined in a time-division manner with one piece of control information data. Specifically, for example, 4-bit control information data is inserted for each plurality of 8-bit main data.

This point will be explained in more detail.

Now, if we consider the sampling frequency required for PCM (A/D conversion), the frequency components included in an audio signal, for example, a music signal, and the fluctuating frequency components of the level (envelope) of the music signal, we can see that Fig. 3 As shown in the figure, the sampling pulse SP is normally 30KHz to 5KHz.
Although the music signal MS has a very high frequency of 0 KHz, the energy is concentrated in the frequency components of 200 Hz to 3 KHz, and the change in the level (envelope) ME is 0.
It has a very low frequency of about 5Hz to 300Hz. Therefore, the control information data corresponding to the envelope component of the main data corresponding to the audio signal data sampled at a high frequency is at a sufficiently low frequency.
In other words, it fluctuates over long periods. Therefore, even if one piece of control information data is combined with, for example, 100 pieces of main data, it is possible to transmit the control information data without running out of information with respect to the main data, and at least 100 pieces of control information data can be combined. It is sufficient to combine one piece of control information data with each piece of main data. A major feature of the present invention is that one control information data is synthesized from a large number of main data in this way.

Furthermore, since the envelope component generally has a sufficiently narrower range of change than the original signal, it is sufficient for the control information data to have the number of bits less than the main data.

Furthermore, during transmission, in order to make it easier to identify control information data from the transmitted data, multiple pieces of main data are treated as one frame, and the main data is handled in frame units, and control information data is attached to each frame. Alternatively, the control information data may be distributed within the main data group in a predetermined manner, or may be combined with a code for identifying it as control information data. Furthermore, either one of the two pieces of data may be delayed relative to the other and combined for transmission so that the control information data has a correct time relationship with respect to the main data during transmission/reception.

On the other hand, in the receiving device that is the receiving side of the transmission signal sent via the transmission system, the received data is discriminated and separated into main data and control information data by the signal processing/separation circuit 17, and one main After the data is subjected to necessary signal processing, it is D/A converted by a D/A converter 18. The other control information data discriminated and separated by the signal processing/separation circuit 17 is similarly D/A converted by the D/A converter 19.
Further, after temporal adjustment is performed by the time constant circuit 20, the signal is given to the variable gain amplifier 21 as a control signal. In this way, the output of the D/A converter 18 is level-variably controlled by the variable gain amplifier 21 in accordance with the output of the time constant circuit 20, and an audio signal of the correct level is restored and output from the output terminal A0. This output audio signal has reduced noise.

The variable gain characteristics of the variable gain amplifier 21 on the receiving side, that is, the decoding side, must be opposite to those of the variable gain amplifier 11 on the transmitting side, that is, the encoding side. In other words, this transmission/reception relationship is shown in a mathematical model as shown in Figure 4.If the variable gain amplifier 11 on the transmitting side is a multiplier circuit, the variable gain amplifier 21 on the receiving side is a dividing circuit, and the transmitting side is a logger. If it is a (logarithmic) conversion circuit, the receiving side will be an antilog (antilogarithmic) conversion circuit.

In this way, by inserting one piece of gain control information data into a large number of main data, it is possible to reduce quantization noise etc. compared to the information signal (information of the audio signal) and transmit it. , the receiving side can restore the correct signal.

Note that although the circuit for error correction of transmission data and the memory for interleaving transmission data are not particularly described above, these may be added to the combining/signal processing circuit 16 of the transmitting device as necessary. ,
Needless to say, it is provided in the signal processing/separation circuit 17 or the like of the receiving device.

Also, the transmission/reception process, for example before A/D conversion and D/A
The PCM conversion system may be modified in various ways, such as pre-emphasis and de-emphasis may be performed after conversion, or sample-and-hold circuits may be used for the time constant circuits 13 and 20. In particular, in a PCM conversion system, the A/D conversion section may be based on DPCM (differential PCM), ΔM (delta modulation), or other digital encoding methods instead of ordinary A/D conversion.

Also, a level detector 12 on the encoding side, that is, on the transmitting side.
is a digital level detection method (a method that performs level detection by digitizing the signal and then determining the digital value)
Alternatively, it may be used as a level detection means using a digital peak hold method (a method in which a signal is digitized and then the peak value is detected and held by judging the digital value).
Furthermore, other analog level variable control means or digital level variable control means may be used in place of the variable gain amplifier.

FIG. 5 shows an example of a system in which the level detection means, level variable control means of the transmitter, and level variable control means of the receiver are digitized.

In FIG. 5, the transmitting device transmits an input audio signal to A
/D converter 22 converts it into digital original data with a sufficient number of bits, for example 15 bits, and then digitally detects the maximum level or average level with digital level detection means 23 to obtain control information data of 4 bits, for example. Then, the digital level variable control means 24 digitally controls the level of the original output data of the A/D converter 22 based on the control information data to obtain, for example, 8-bit main data, and converts this main data and the control information. The data is sent to the transmission system by the combining means 25 so that one control information data corresponds to a large number of main data. When controlling the level of a large number of data using the digital level variable control means 24, it may be preferable to perform the control after obtaining the level control coefficient (level control information), and in such a case, it is indicated by a broken line. The original data may be delayed using a storage means 26 such as a RAM (random access memory).

On the other hand, the receiving device separates and extracts the main data and the control information data from the transmission signal received from the transmission system by the separating means 27,
A digital level variable control means 28 performs digital level variable control on the main data with control characteristics opposite to those on the transmitting side based on the control information data, and a D/A converter 29 converts the main data into an analog signal to obtain an output audio signal.

Here, an example of the above-mentioned digital level variable control will be explained in detail.

Variable level control is, in principle, multiplication of controlled data and control data if it is variable gain control of the signal path, so even if this is done digitally, in principle, for example, if you follow the example above, 15 bits What is necessary is to multiply the original data by the 4-bit control information. To simplify this multiplication, we use 2
Utilizing the characteristics of integer data, gain control steps are 2x, 4x, 8x... or 1/2, 1/4, 1/8
A possible method is to take a value of 2n (n is an integer) such as . In this method, if the data is a binary number, doubling the data requires shifting the data by 1 bit to the higher order side, and quadrupling the data by shifting the data by an additional 1 bit (2 bits in total). When using this method, for example, 1
It is only necessary to detect how many bits of the 5-bit original data are occupied by significant data. Specifically, since it is sufficient to detect the bit position of the most significant "1" data, it can be easily detected using a so-called priority encoder or the like.

In other words, if significant data exists in the shaded part of the 15-bit original data as shown in Figure 6 (a) to (c), then in the case of Figure 6 (a), the significant data is the original data. Of these, 6 bits are occupied, and if 8 bits are taken as main data, the lower 8 bits are sent as is as main data, and the control level, that is, the shift amount at this time, is "7".
becomes.

If the number of significant data is 8 or less, the control level is set to "7".

In the case of (b) in the same figure, the number of significant data is 9 bits, so the control level is "6" and 8 bits are taken as the main data, so the least significant bit (LSB) of the original data is ignored and this part is considered an error. However, it is a sufficiently small value compared to the value of the main data. In the case of figure (c), the number of significant data is 15.
The control level is "0", and in this case, the lower 8 bits of the original data are ignored. The above control level may be used as control information data. In this case, since the number of types of control levels is 8=2■ at maximum, the control information data only needs to be 3 bits.

In addition, in this case, it is also possible to determine a certain time width in advance, determine the control level in correspondence with the maximum level of the original data within that time width, and use this as control information data, so that the maximum data value Since it is preferable to perform variable gain control after obtaining , it is desirable to perform control after the original data within this time range is temporarily stored in a RAM or the like.

Further, in FIG. 5, level variable control on either the transmitting side or the receiving side may be performed in an analog manner. Of course, digital level variable control and analog level variable control may be combined to realize level variable control in the transmitter or receiver.

Furthermore, by inserting a differentiating circuit at the input end of the configuration shown in Figure 5, inserting an integrating circuit at the output end, or incorporating a local decoder into the A/D conversion section, DPCM conversion or similar conversion is performed. You can do it like this.

Further, in FIG. 5, the relationship between the level detection section and the level variable control section is feedforward, but in FIG. 1, it is feedback, and either method may be adopted.

Transmission systems also include modulation/demodulation systems such as FM (frequency modulation) and AM (amplitude modulation) other than normal transmission channels, recording/reproduction systems using recording media and memory, and other conversion systems. When using a transmission line, it can be implemented in substantially the same manner as described above, and can be used not only for reducing quantization noise but also for reducing noise generated or mixed in the transmission system.

Although the above description focuses on the case where an audio signal, especially a music signal, is used as the original signal, other audio signals and other analog signals such as video signals, measurement signals, etc. can also be used as audio signals such as music signals. As long as they have similar characteristics, they can be implemented in substantially the same manner as described above.

In addition, the present invention can be implemented with various modifications without changing the gist thereof.

〔Effect of the invention〕

According to the present invention, a transmission method and a transmission method capable of effectively reducing noise components such as quantization noise generated or mixed in a transmission path etc. when transmitting a signal by digitizing an analog signal and returning it to the original analog signal. It is possible to provide a device that can effectively implement the transmission method.

[Brief explanation of the drawing]

Fig. 1 is a system block diagram for explaining the noise reduction method in conventional PCM transmission, Fig. 2 is a system block diagram showing the configuration of an embodiment of the present invention, and Fig. 3 is a system block diagram showing the principle of the embodiment. A waveform diagram for explaining the main parts, FIG. 4 is a diagram showing a mathematical model of the same embodiment, and FIG. 5 is a system block diagram showing the configuration of another embodiment of the present invention.
FIGS. 6(a) to 6(c) are bit format diagrams for explaining an example of digital level variable control used in the same embodiment. 11, 21... Variable gain amplifier, 12... Level detector, 13, 20... Time constant circuit, 14, 15, 22
... A/D converter, 16... Synthesis/signal processing circuit, 17... Signal processing/separation circuit, 18, 19, 29
... D/A converter, 23... Level detection means,
24, 28...Level variable control means, 25...Composition means, 27...Separation means.

Claims (9)

[Claims] (1) Obtaining a first digital signal by converting an analog signal into a digital value and performing first level variable control so that the final digital value becomes a substantially constant value, and at the same time obtaining the first level variable control. The control information in the first digital signal is a second digital signal consisting of a digital value having a smaller number of bits than the first digital signal, and these first and second digital signals are
The synthesized signal is synthesized at a ratio of the number of data that is sufficiently small for the digital signal of The first digital signal obtained is converted into an analog signal, and a second level variable control having substantially opposite characteristics to the first level variable control is performed based on the extracted second digital signal. A signal transmission method characterized by restoring analog signals. (2) In the signal transmission system according to claim 1, when obtaining the first digital signal from the analog signal, the analog signal is subjected to analog-like first level variable control, so that the analog signal has a substantially constant level. After signal,
A signal transmission system characterized in that the first digital signal is obtained by converting this into a digital value. (3) In the signal transmission system according to claim 1, when obtaining the first digital signal from the analog signal, the analog signal is preliminarily converted into digital data having a larger number of pits than the first digital signal. , a signal transmission system characterized in that the first digital signal is obtained by digitally applying a first level variable control to the preliminary conversion data. (4) In the signal transmission method according to any one of claims 1 to 3, in restoring the analog signal from the received and extracted first and second digital signals, After converting the first and second digital signals into analog information, a second level variable control is performed in an analog manner based on these analog information to restore the analog signal. method. (5) In the signal transmission system according to any one of claims 1 to 3, in restoring the analog signal from the received and extracted first and second digital signals, The signal is characterized in that the second level variable control is performed digitally based on the first and second digital signals obtained, and then the obtained digital information is converted into an analog value to restore the analog signal. Transmission method. (6) An A/D conversion means for converting an analog signal into pre-converted digital data, and a digital (first)
A first digital signal having a smaller number of bits and a substantially constant level than the pre-converted digital data is obtained by performing level variable control, and the control information in this (first) level variable control is used to obtain the first digital signal. level variable control means for obtaining a second digital signal having a smaller number of bits than the second digital signal; 1. A transmitting device comprising: a signal combining means for inserting a signal and applying the signal to a transmission system. (7) In the transmitting device according to claim 6,
The level variable control means includes means for obtaining a first digital signal by extracting a predetermined number of higher order bits of the valid bits of the pre-converted digital data, and a bit position in the pre-converted data from which the first digital signal was extracted in the means. and means for obtaining a second digital signal having a smaller number of bits than the first digital signal. (8) a first digital signal obtained by converting an analog signal into a digital value and performing first level variable control so that the final digital value becomes a substantially constant value; A second digital signal corresponding to control information in level variable control and consisting of a digital value having a smaller number of bits than the first digital signal is synthesized at a rate such that the second digital signal has a sufficiently smaller number of bits. A receiving device for receiving a transmission signal given to a transmission system and restoring the original analog signal, comprising: a signal separating means for separately extracting the first and second digital signals from the received signal; Digitally converts the first digital signal extracted by the separating means into a second digital signal extracted by the signal separating means as control information, which has characteristics substantially opposite to those of the first level variable control. level variable control means for obtaining digital data having a larger number of bits than the first digital signal by performing level variable control as described above; and D/A conversion means for converting the digital data obtained by the level variable control means into analog values. A receiving device comprising: (9) The first digital signal consists of data of a predetermined number of upper bits of the pre-converted digital data obtained by converting the analog signal, and the second digital signal consists of the data of the predetermined number of bits in the pre-converted digital data. In the receiving device according to claim 8, the level variable control means includes means for shifting the data of the first digital signal in accordance with the second digital signal to obtain digital data; and means for converting digital data obtained by this means into analog values.