JPH0758705A - Audio signal transmission equipment - Google Patents

Abstract

PURPOSE:To send out an audio signal of high quality in real time without spoiling the quality of the sent audio data when the audio signal is sent out by effectively utilizing characteristics of a transmission line having the good frequency characteristics by limiting the band of a sent digital signal to an audio frequency band, and then changing the sampling frequency and outputting the signal. CONSTITUTION:A digital audio tape recorded 1 inputs an analog audio signal S1 to a low-pass filter 4 through an input terminal 3, and limits the band to the frequency band which is twice that of a normal digital audio tape recorder and outputs the signal. Further, the output signal of the low-pass filter 4 is inputted to an analog-digital converting circuit 5 and converted into a digital signal with the specific sampling frequency and outputted. Consequently, the effect that requantization noises are shaped so that the noises are suppressed in the audio frequency band is maintained and the digital signal D4 which is converted with the sampling frequency and transmitted can be sent out.

Description

Detailed Description of the Invention

[0001]

[Table of Contents] The present invention will be described in the following order. Field of Industrial Application Conventional Technology Problem to be Solved by the Invention Means for Solving the Problem (FIG. 1) Action (FIG. 1) Example (1) Configuration of Example (FIGS. 1 to 11) (2) Effects of Examples (3) Other Examples Effects of the Invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio signal transmission device, and can be applied to, for example, a digital audio tape recorder for converting an audio signal into a digital signal at a high sampling frequency and recording it on a magnetic tape.

[0003]

2. Description of the Related Art Conventionally, in a digital audio tape recorder, an audio signal having a high sound quality can be recorded and reproduced by converting an audio signal into a digital signal and recording it on a magnetic tape.

That is, this digital audio tape recorder samples 16-bit audio signals by sequentially sampling the audio signals at a sampling frequency of 48 [kHz] or 44.1 [kHz] and performing analog digital conversion processing. Convert to digital signal. Since it is said that the frequency band of 20 Hz to 20 kHz is the human audible frequency band, the sampling frequency is selected in this way, and the digital audio tape recorder has a human audible frequency band. It is designed to convert an audio signal into a digital signal in substantially equal frequency bands.

Further, the digital audio tape recorder divides the digital signal into a predetermined block unit, adds an error correction code in the block unit, and performs an interleave process to form recorded data. As a result, the digital audio tape recorder drives the magnetic head with this recording data, thereby sequentially recording this recording data on the magnetic tape.

Thus, the digital audio tape recorder converts the reproduction signal output from the magnetic head into binary data at the time of reproduction, and then executes a processing procedure reverse to that at the time of recording to demodulate the original audio signal. Therefore, it is possible to effectively avoid the sound quality deterioration during recording and reproduction.

[0007]

In this type of digital audio tape recorder, the rotational speed of the rotary drum is set to twice the normal rotational speed and the magnetic tape running speed is set to double the normal rotational speed. It has been proposed to set and set a higher audio quality audio signal to be recorded / reproduced (hereinafter referred to as a double speed recording / reproduction digital audio tape recorder).

According to this double-speed recording / reproducing digital audio tape recorder, the sampling frequency can be set to be twice as high as that of the normal digital audio tape recorder, and the frequency band in which recording / reproduction is possible is set to the normal digital audio tape. It can be expanded to twice the size of a recorder. Therefore, according to this digital audio tape recorder for double-speed recording / playback, the cutoff frequency of the anti-aliasing filter used for band limitation can be set to a frequency sufficiently higher than the audible frequency band, and the conventional digital audio tape recorder can be used. In comparison, the deterioration of the transient characteristic in the audible frequency band can be significantly reduced.

However, in this double speed recording / reproducing digital audio tape recorder, since the number of quantizing bits that can be recorded / reproduced is the same as that of the conventional digital audio tape recorder, the frequency characteristic can be improved, but the conventional digital audio tape recorder is improved. However, the amplitude characteristic is not improved at all. If the characteristics of this digital audio tape recorder for double-speed recording and playback can be effectively utilized and the amplitude characteristics can be easily improved, the sound quality of this kind of digital audio tape recorder can be further improved. It is considered that the usability of the digital audio tape recorder can be improved and the application fields can be expanded.

However, in a digital audio tape recorder for double-speed recording / reproduction, the data transfer rate during reproduction is 2 times that of an ordinary digital audio tape recorder.
Therefore, when reproducing data is transferred by a digital audio interface standardized for a digital audio signal, the transfer time is doubled. In this case, there is a problem that the reproduced audio data cannot be transmitted in real time even if the frequency characteristic and the amplitude characteristic can be improved.

The present invention has been made in consideration of the above points, and when transmitting a high-quality audio signal by effectively utilizing the characteristics of a transmission path having a good frequency characteristic, the quality of the transmitted audio data. The present invention is intended to propose an audio signal transmission device capable of transmitting in real time without damaging the signal.

[0012]

In order to solve such a problem, in the present invention, in the audio signal transmission device 1 for receiving the transmission digital signal D4 transmitted through the predetermined transmission line 2, the transmission line 2 is Predetermined sampling frequency 2
It is formed so as to transmit a transmission digital signal D4 of f _S and a predetermined number of bits (16 bits).
f _S is a frequency at which the transmission digital signal D4 having a frequency band higher than the audible frequency band can be transmitted. The transmission digital signal D4 has a sampling frequency of 2f _S and has more bits than the number of bits (16 bits). The digital audio signal D2 is re-quantized and generated, and at the time of the re-quantization, re-quantized noise is generated by noise shaping so as to be suppressed in the audible frequency band. A digital filter 20 that outputs the transmission digital signal D4 transmitted through the transmission line 2 with band limitation in an audible frequency band, and a digital signal D5 output from the digital filter 20 are converted into a predetermined sampling frequency f _S. And a sampling frequency conversion circuit 21 for outputting the output.

Further, in the second invention, the transmission line 2 is
The magnetic recording / reproducing apparatus 2 records and reproduces the transmission digital signal D4 on a magnetic tape, and the sampling frequency of the transmission line 2 is a frequency 2f _S capable of recording / reproducing a frequency band twice the audible frequency band, The sampling frequency conversion circuit 21
The digital signal D5 output from the digital filter 20 is converted into a sampling frequency f _S that is ½ of the sampling frequency 2 f _S of the transmission line 2 and output.

[0014]

If the transmission digital signal D4 transmitted through the transmission line 2 is band-limited in the audible frequency band and then converted into a predetermined sampling frequency f _S and output, requantization noise is generated in the audible frequency band. It is possible to maintain the effect of noise shaping so that the digital signal D4 is transmitted after being converted into the sampling frequency f _S and transmitted. This can improve the perceptual resolution by noise shaping.
Thus, the audio data thus transmitted can be transmitted in real time without impairing the quality.

Further, by applying a magnetic recording / reproducing device as a transmission line, effectively using the characteristics of a digital audio tape recorder for double-speed recording / reproducing, audio data having improved frequency characteristics and amplitude characteristics can be obtained without degrading the quality. It can be sent in real time.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

(1) Configuration of the Embodiment In FIG. 1, reference numeral 1 denotes a digital audio tape recorder as a whole, in which a digital audio tape recorder 2 for double-speed recording / playback is used to record an audio signal S1 and further to record the audio signal S2. To play.

That is, the digital audio tape recorder 1 inputs the analog audio signal S1 to the low-pass filter (LPF) 4 through the input terminal 3, where the frequency is twice as high as that of a normal digital audio tape recorder. Bandwidth is limited and output. Further, the digital audio tape recorder 1 inputs the output signal of the low-pass filter 4 into an analog digital conversion circuit (A / D) 5 and converts it into a digital signal.

In this embodiment, the digital audio tape recorder 2 for double-speed recording / reproducing is formed so as to record / reproduce a digital audio signal having a sampling frequency of 2f _S (2f _S = 96 [kHz]). sampling frequency of the analog-to-digital converter circuit 5, if indicated a sampling frequency of 32 times the frequency of the sampling frequency of the digital audio tape recorder 2 (i.e. normal digital audio tape recorder in f _S, at a frequency of 64f _S Will be selected. As a result, in the digital audio tape recorder, the sampling frequency is set to a sufficiently high frequency with respect to the upper limit frequency of the audible frequency band and further to the recordable upper limit frequency of the digital audio tape recorder 2 for double-speed recording / playback. Therefore, it is possible to effectively avoid the sound quality deterioration of the audio signal.

Further, the digital audio tape recorder 1 outputs the output data D1 of the analog digital conversion circuit 5 to the decimation filter 6, where the sampling frequency is reduced and the number of bits of the output data is increased accordingly. As a result, the digital audio signal D1 is converted into a digital audio signal D2 having a sampling frequency of 2f _S 20 bits. As a result, the digital audio tape recorder 1 uses the decimation filter 6 to change the frequency band of the digital audio signal D1.
Digital audio tape recorder 2 for double-speed recording and playback
It is designed to be reduced to a recordable frequency band.

Thus, if the digital audio tape recorder 2 for double-speed recording and reproduction is used, the sampling frequency is 2f.
A digital audio signal of _S (96 [kHz]), 16 bits can be recorded / reproduced, whereby the frequency band in which recording / reproduction can be performed can be doubled as compared with a normal digital audio tape recorder. On the other hand, the digital audio tape recorder 1 has a decimation filter 6
The output data D2 is output to the noise shaper 7, where the number of bits of this digital signal is reduced to 16 bits.

As a result, the digital audio tape recorder 1 outputs the output data of the noise shaper 7 to the digital audio tape recorder 2 for double-speed recording / reproduction to record the data, and the frequency that can be recorded by the conventional digital audio tape recorder is recorded. Compared to the band
The frequency band is doubled to record the audio signal S1. Further, in this embodiment, when the number of bits of the audio data D2 is reduced by the noise shaper 7, a so-called noise shaping method is applied to improve the perceptual resolution.

That is, as shown in FIG. 2, the noise shaper 7 quantizes the input data D 2 sequentially input by the quantizer 9.
Then, the input data D2 is requantized and converted into output data D3, whereby 20-bit input data D2 is converted into 16-bit output data D3. At this time, the noise shaper 7 detects the quantization error data DZ generated when requantizing by the quantizer 9 with the subtraction circuit 10, and outputs this error data DZ to the subtraction circuit 12 via the noise filter 11. To do. Further, the noise shaper 7 is configured so that the subtraction circuit 12 inputs the input data D
The error data DZ is subtracted from 1, and the quantizer 9
Noise filter 11 to quantize noise when requantizing with
It can be set to a characteristic determined by the frequency characteristic of.

That is, as shown in FIG. 3, if the frequency characteristic of the noise filter 11 is selected so that the amplitude characteristic is suppressed in the audible frequency band and the amplitude characteristic is emphasized in the frequency band higher than the audible frequency band, noise is reduced. In the output data D3 of the shaper 7, quantization noise in the audible frequency band can be suppressed. That is, in the digital audio tape recorder 1, the quantization noise can be driven to a band higher than the audible frequency band, whereby the quantization noise can be formed to be distributed above the upper limit frequency of the audible frequency band. As a result, it is possible to audibly reduce quantization noise during requantization.

Therefore, in the digital audio tape recorder 1, the input audio signal S1 is simply converted into a 16-bit digital audio signal having a sampling frequency of 2f _S and a digital audio tape recorder 2 is used.
As compared with the case of recording with the above method, it is possible to audibly obtain a resolution higher than the number of bits that can be recorded within the audible frequency band. As a result, the digital audio tape recorder 1 records and reproduces a high-quality audio signal by effectively utilizing the characteristics of the digital audio tape recorder 2 of double-speed recording and reproduction capable of recording and reproducing a frequency band twice the audible frequency band. can do.

Further, in this embodiment, the digital audio tape recorder 1 concretely forms a noise shaper 7 as shown in FIG. 4, whereby the adaptive predictive coding method is applied to further improve the auditory sense. Reduce noise. That is, the noise shaper 7 receives the input data D
2 is input to the energy analyzer 14, and the frequency distribution of the input data D2 is detected by cumulatively adding the input data D2 using a predetermined time window function.

The coefficient calculator 15 is an energy analyzer 14
By switching the coefficient of the noise filter 11 based on the detection result of, the quantization noise of the output data D2 is reduced so as to correspond to the frequency characteristic of the input data D2. The characteristics of the noise filter 11 are switched so as to follow the above. That is, as shown in FIG. 5, when the energy of the input data D1 which is an input signal is concentrated in the low frequency band, the coefficient calculator 15 reduces the quantization noise in the low frequency band as shown in FIG. The coefficient of the noise filter 11 is set so that the quantization noise of the output data D2 is reduced, and the quantization noise is set to be distributed in the audible frequency band or higher.

On the other hand, as shown in FIG. 7, when the energy is concentrated in the high range, the coefficient calculator 15 operates as shown in FIG.
As shown in, the coefficient of the noise filter 11 is set so as to reduce the quantization noise in the mid-high range rather than the low range, thereby reducing the quantization noise of the output data D2, and the quantization noise is further reduced in the audible frequency band. Set so that it is distributed above.

On the other hand, the digital audio tape recorder 2 for double-speed recording / reproduction sets the rotation speed of the rotary drum and the running speed of the magnetic tape to twice the speed of a normal digital audio tape recorder, and further performs the entire signal processing. The speed is set to be twice as high as that of a normal digital audio tape recorder, so that the sampling frequency of 96 [kHz is output from the noise shaper 7.
z], a 16-bit digital audio signal D3 is sequentially recorded on the magnetic tape.

On the other hand, at the time of reproduction, the digital audio tape recorder 2 operates at the same processing speed as that at the time of recording, thereby sequentially processing the reproduced signals output from the magnetic head and sampling frequency 96 [kHz]. , 16-bit digital audio signal D4 is output. The oversampling filter 17 uses the digital audio signal D.
4 is band-limited and output, and the digital-analog conversion circuit 18 converts the output data of the filter 17 into an analog signal and outputs it.

As a result, the digital audio tape recorder 1 outputs this analog signal to the low pass filter 19.
The audio signal S2 can be reproduced by outputting the audio signal S2 through the audio signal S2. At this time, in the audio signal S2, a method of adaptive predictive coding is applied so that the quantization noise is suppressed in the audible frequency band. By reducing the quantization noise of the lever, the sound quality can be remarkably improved as compared with the case where the audio signal is recorded and reproduced only by using the digital audio tape recorder 2 for double-speed recording and reproduction.

By the way, when the audio data reproduced in this manner is transmitted in the form of a digital signal, the reproduction data D4 output from the digital audio tape recorder 2 for double-speed recording / reproduction may be transmitted. It becomes impossible to use the standardized digital audio interface. Therefore, in this embodiment, the digital audio tape recorder 1 converts a digital signal D4 of 16 bits with a sampling frequency of 2f _S into a digital signal D6 of 20 bits with a sampling frequency f _S satisfying the standard of the digital audio interface. And output.

Further, in this conversion, the digital audio tape recorder 1 band-limits the digital signal D4 by using the digital filter 20, and then reduces the sampling frequency f _S by using the decimation filter 21. The digital signal D4 can be converted into the digital signal D6 without impairing the quality of the digital signal D4.

That is, the digital filter 20 receives the 16-bit digital signal D4 with a sampling frequency of 2f _S output from the digital audio tape recorder 2 and performs a convolution operation between consecutive audio data. The band of the digital signal D4 is band-limited to the frequency 24 [kHz] which is an audible frequency band. At this time, the digital filter 20 outputs the upper 20 bits of the arithmetic processing result obtained in this convolution operation to the subsequent decimation filter 21 to expand the number of bits of the digital signal D4 to 20 bits and output it. To do.

As a result, as shown in FIG. 9, the digital signal D4 in which the quantization noise is distributed above the audible frequency band.
10, the quantization noise having a frequency of 24 [kHz] or higher is suppressed and is output to the subsequent decimation filter 21.

The decimation filter 21 selectively outputs the output data D5 of the digital filter 20 so that the output data D5 can be sampled at a sampling frequency of 48 [kHz] adapted to the digital audio interface.
z], converted to 20-bit audio data D6 and output. As a result, in the audio data D6, as shown in FIG. 11, the quantization noise starts to fold back from the frequency of 48 [kHz]. At this time, the band is limited by the digital filter 20 in advance, so that the audible frequency band becomes , The effect of noise shaping can be maintained.

That is, when the digital signal D4 output from the digital audio tape recorder 2 is simply converted into an audio signal having a sampling frequency of 48 [kHz], folding noise up to the quantization noise distributed outside the audible frequency band of the digital signal D4 is generated. Will be mixed in the audible frequency band. That is, at the time of recording, the quantized noise that has been driven outside the audible frequency band by noise shaping will be mixed into the audible frequency band, and the audio data transmitted via the digital audio interface will have noise No effect will be obtained.

On the other hand, if the audio signal is converted into an audio signal having a sampling frequency of 48 [kHz] after band limiting in the audible frequency band as in this embodiment, the digital audio is maintained while maintaining the effect of noise shaping. It is possible to transmit the digital signal D6 via the interface, and thereby to effectively utilize the characteristics of the transmission path having a good frequency characteristic and to transmit the quality of the transmitted audio signal when transmitting the high quality audio signal. It can be delivered in real time without loss.

Thus, even with the audio data D6 transmitted through the digital audio interface, a bit resolution of 16 bits or more, which is the recording / reproducing bit of the digital audio tape recorder 2, can be audibly obtained.

(2) Effects of the Embodiments According to the above configuration, the audio data recorded by requantizing so that the quantization noise is distributed over the audible frequency band by applying the noise shaping method is reproduced. In this case, by limiting the playback data to the audible frequency band and then converting it to the sampling frequency of the digital audio interface, the audio data can be transmitted while maintaining the effect of noise shaping. Can be transmitted in real time without impairing the quality of the reproduced audio signal.

(3) Other Embodiments In the above embodiments, the case where the energy distribution of the digital signal D2 is detected using the time window function has been described, but the present invention is not limited to this, and the digital signal is not limited to this. Various energy distribution detection methods can be widely applied, such as when the energy distribution is detected by dividing the band of D2 and when the fast Fourier transform method is applied.

Further, in the above-mentioned embodiment, the case where not only the noise-sheathing but also the method of adaptive prediction coding is applied to record the audio signal is described, but the present invention is not limited to this. In addition to this, a pre-emphasis circuit and a de-emphasis circuit may be used to further improve the sound quality.

Furthermore, in the above-mentioned embodiments, the case where the present invention is applied to a digital audio tape recorder to record and reproduce a digital audio signal has been described, but the present invention is not limited to this, and a recording medium such as an optical disk can be used. When recording and reproducing a digital audio signal via
Further, it can be widely applied to the case of transmitting an audio signal through various transmission lines other than such a recording medium.

[0044]

As described above, according to the present invention, regarding the transmission digital signal transmitted by noise shaping so that the requantization noise is suppressed in the audible frequency band, the transmission digital signal is transmitted in the audible frequency band. After the band is limited by, the sampling frequency is converted and output, so that the high-quality transmission digital signal transmitted by effectively utilizing the characteristics of the transmission line can be given a predetermined interface without deteriorating its quality. Thus, it is possible to obtain an audio signal transmission device which can be transmitted in real time via.

[Brief description of drawings]

FIG. 1 is a block diagram showing a digital audio tape recorder according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the noise shaper.

FIG. 3 is a characteristic curve diagram showing the characteristics of the filter.

FIG. 4 is a block diagram showing a specific configuration of a noise shaper.

FIG. 5 is a characteristic curve diagram showing a case where energy is concentrated in a low range.

FIG. 6 is a characteristic curve diagram showing the frequency characteristic of the filter in that case.

FIG. 7 is a characteristic curve diagram showing a case where energy is concentrated in a high range.

FIG. 8 is a characteristic curve diagram showing frequency characteristics of the filter in that case.

9 is a characteristic curve diagram for explaining a digital signal output from the digital audio tape recorder 2. FIG.

FIG. 10 is a characteristic curve diagram for explaining the operation of the digital filter.

FIG. 11 is a characteristic curve diagram for explaining the operation of the decimation filter.

[Explanation of symbols]

1, 2, 20 ... Digital audio tape recorder, 4, 19 ... Low-pass filter, 5 ... Analog digital conversion circuit, 6 ... Decimation filter, 7
…… Noise shaper, 17 …… Oversampling filter, 18 …… Digital analog conversion circuit, 9 ・ ・ ・
... Quantizer, 11 ... Noise filter, 14 ... Energy analysis circuit, 15 ... Filter coefficient calculation circuit, 20 ...
… Digital filter, 21… Decimation filter.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Makoto Yamada 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation (72) Masaaki Ueki 6-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Within the corporation

Claims (2)

[Claims] 1. An audio signal transmission device for receiving a transmission digital signal transmitted via a predetermined transmission line, wherein the transmission line transmits a transmission digital signal of a predetermined sampling frequency and a predetermined number of bits. The sampling frequency is a frequency capable of transmitting the transmission digital signal having a frequency band equal to or higher than the audible frequency band, and the transmission digital signal is the sampling frequency and a bit greater than the bit number. The digital audio signal is generated by requantizing a large number of digital audio signals, and at the time of the requantization, it is generated by noise shaping so that the requantization noise is suppressed in the audible frequency band. Is a digital signal that outputs the transmission digital signal transmitted through the transmission line by band limiting in an audible frequency band. Filter and, audio signal transmission apparatus characterized by comprising a sampling frequency converting circuit for converting the digital signal to a predetermined sampling frequency output from the digital filter. 2. The transmission line is a magnetic recording / reproducing device for recording and reproducing the transmission digital signal on a magnetic tape, and the sampling frequency of the transmission line is 2 in the audible frequency band.
The sampling frequency conversion circuit converts the digital signal output from the digital filter into a sampling frequency half the sampling frequency of the transmission line. The audio signal transmission device according to claim 1, wherein the audio signal transmission device outputs the audio signal.