JPH0723007A - Audio signal transmitting device - Google Patents

Abstract

PURPOSE:To effectively utilize a characteristic of a transmission line and to improve an amplitude characteristic by executing noise shaping so as to suppress a requantizing noise by an audio frequency band, at the time of requantizing a digital audio signal. CONSTITUTION:A digital audio tape recorder 1 records an audio signal S1 by using a double speed sound recording/reproducing digital audio tape recorder 2, and reproduces a recorded audio signal S2. A sampling frequency of an A/D converting circuit 5 is selected to a frequency of 32 folds of a sampling frequency of this tape recorder 2, and the tape recorder 1 outputs output data D1 of the A/D converting circuit 5 to a decimation filter 6, reduces the sampling frequency therein, and also, increases the number of bits of output data. Also, output data D2 of the decimation filter 6 is outputted to a noise shaper 7, and the number of bits of a digital signal is reduced. In such a way, the resolution of the number of bits or more of a transmission digital signal is obtained in an audio frequency band.

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 (FIGS. 1 and 9) Action (FIGS. 1 and 9) Working Example (1) First Working Example (FIG. 1) And FIG. 8) (2) Second embodiment (FIGS. 9 to 11) (3) Other embodiments Effect 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 the frequency range of 20 [Hz] to 20 [kHz] is said to be the human audible frequency band, the digital audio tape recorder selects the sampling frequency in this way and is almost the same as the human audible frequency band. In equal frequency bands,
It is designed to convert audio signals into digital signals.

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 and reproduced (hereinafter referred to as a double-speed recording and 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 and reproduced is the same as that of the conventional digital audio tape recorder, the frequency characteristic can be improved, while the conventional digital audio tape recorder is 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.

The present invention has been made in consideration of the above points, and when transmitting an audio signal through a transmission line having a good frequency characteristic, the characteristic of this transmission line is effectively used to obtain an amplitude characteristic. The present invention intends to propose an audio signal transmission device that can be easily improved.

[0011]

In order to solve such a problem, according to the present invention, in an audio signal transmission device 1 for transmitting a digital audio signal D2 via a predetermined transmission line 2, the transmission line 2 is a predetermined sample. Frequency 2f _S
And a sampling frequency of 2f _S which is formed so as to transmit a transmission digital signal D3 of a predetermined number of bits (16 bits).
Is a frequency at which a transmission digital signal D3 having a frequency band higher than the audible frequency band can be transmitted. The audio signal transmission device 1 has a sampling frequency of 2f _S and a digital number of bits larger than the number of bits (16 bits). By re-quantizing the audio signal D2 to generate a transmission digital signal D3 and transmitting the transmission digital signal D3 via the transmission line 2, the digital audio signal D3 is transmitted via the transmission line 2 and the digital audio signal D3 is transmitted. D2
Is re-quantized, noise shaping is performed so that re-quantized noise is suppressed in the audible frequency band.

Further, in the second invention, the energy distribution of the digital audio signal D2 is detected, and the frequency characteristic of noise shaping is switched based on the detection result.

Further, in the third invention, when the transmission digital signal D3 is transmitted through the transmission line 2, the pre-emphasis circuit 21 is used to emphasize and record a frequency band higher than the audible frequency band of the transmission digital signal D3. The data is recorded on the medium and is output via the de-emphasis circuit 22 when the transmission digital signal recorded from the recording medium is reproduced.

Further, in the fourth invention, the transmission line 2 is
The magnetic recording / reproducing apparatus 2 records a transmission digital signal D3 having a sampling frequency of 2f _S and a bit number (16 bits) on a magnetic tape, and the sampling frequency of 2f _S records and reproduces a frequency band which is twice the audible frequency band. Frequency.

[0015]

The digital audio signal D2 is re-quantized to generate the transmission digital signal D3, and the transmission digital signal D3 is transmitted through the transmission line 2. When the digital audio signal D2 is re-quantized, it is re-quantized. If noise shaping is performed so that the quantization noise is suppressed in the audible frequency band, the quantization noise in the audible frequency band can be driven out of the audible frequency band, which results in the number of bits of the transmitted digital signal in the audible frequency band. The above resolution can be obtained in the sense of hearing.

Further, the frequency characteristic of the noise shaper can be changed according to the frequency energy distribution of the input signal to further reduce the quantization noise in the audible frequency band, and the frequency equivalent to the frequency characteristic of the noise shaping can be reduced. The characteristic can be used to pre-amplify the transmitted digital signal to further improve the perceptual resolution.

[0017]

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

(1) First Embodiment In FIG. 1, reference numeral 1 denotes a digital audio tape recorder as a whole, in which an audio signal S1 is recorded by using a digital audio tape recorder 2 for double-speed recording and reproduction, and further recorded audio signal. Play S2.

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 in the case 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 / reproduction 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. As a result, this digital audio signal D1
Is converted into a digital audio signal D2 having a sampling frequency of 2f _S and 20 bits. As a result, the digital audio tape recorder 1 becomes the decimation filter 6
The frequency band of the digital audio signal D1 is reduced to a frequency band recordable by the digital audio tape recorder 2 for double-speed recording / reproduction.

Thus, if the digital audio tape recorder 2 for double-speed recording / 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 / playback to record the data, so that the frequency recorded by the conventional digital audio tape recorder is increased. 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 sequentially input data D2 into a 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 provided with the subtraction circuit 12 for 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 with 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 audibility. 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 range, the coefficient calculator 15 reduces the low frequency quantization noise 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 reproduction signals outputted 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 through the audio signal S2, and at this time, in the audio signal S2, the adaptive prediction coding method is applied so that the quantization noise is suppressed in the audible frequency band. By reducing the quantization noise, the sound quality can be significantly improved as compared with the case where the audio signal is recorded / reproduced simply by using the digital audio tape recorder 2 for double-speed recording / reproduction.

(1-1) Effects of the Embodiments According to the above configuration, the audio signal is requantized by applying the noise shaping method so that the quantization noise is distributed in the audible frequency band or more, and At this time, the adaptive predictive coding method is applied to reduce the quantization noise, so that a 16-bit digital audio signal with a sampling frequency of 2f _S can be audible as compared with the case where the digital audio tape recorder 2 is used. It is possible to perceptually obtain a resolution higher than the number of bits that can be recorded in the frequency band,
This makes it possible to effectively utilize the characteristics of the digital audio tape recorder 2 for double-speed recording / reproduction to record / reproduce high-quality audio signals.

(2) Second Embodiment In FIG. 9 in which parts corresponding to those in FIG. 2 are assigned the same reference numerals, 20 indicates a digital audio tape recorder according to the second embodiment. In the case of this embodiment, Further improve the sound quality by using pre-emphasis and de-emphasis circuits. That is, the digital audio tape recorder 20 has a pre-emphasis circuit 21 arranged between the decimation filter 6 and the noise shaper 7, and correspondingly inserts a day emphasis circuit 22 between the digital audio tape recorder 2 and the oversampling filter 17. To do.

The pre-emphasis circuit 21 is shown in FIG.
0, the frequency amplitude characteristic is selected so as to emphasize the frequency band higher than the audible frequency band, whereas the de-emphasis circuit 22 supplements the frequency characteristic of the pre-emphasis circuit 21 as shown in FIG. like,
The frequency / amplitude characteristic is selected.

That is, if the frequency characteristic of the pre-emphasis circuit 21 is selected so as to emphasize the frequency band higher than the audible frequency band, similar to the frequency characteristic of the noise filter 11 described above with reference to FIG. 3, the recording of the digital audio tape recorder 2 will be described. Within the reproducible frequency band, it is possible to audibly obtain a resolution higher than the number of recordable bits. As a result, it is possible to record / reproduce an audio signal of higher quality.

(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 adaptive predictive coding method is applied and the audio signal is recorded by pre-amphasis is described. However, it is not limited to the above, and only noise sampling may be performed as needed, and either the adaptive predictive coding method or the preamplification method may be combined with the noise shipping.

Further, 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.

[0040]

As described above, according to the present invention, when the digital audio signal is requantized and transmitted, noise shaping is performed so that the requantization noise is suppressed in the audible frequency band. Quantization noise in the audible frequency band can be driven out of the audible frequency band, and as a result, a resolution higher than the number of bits of the transmission digital signal can be audibly obtained within the audible frequency band, thus effectively utilizing the characteristics of the transmission path. As a result, it is possible to obtain an audio signal transmission device whose amplitude characteristics can be easily improved.

[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.

FIG. 9 is a block diagram showing a digital audio tape recorder according to a second embodiment.

FIG. 10 is a characteristic curve diagram showing a frequency amplitude characteristic of a pre-emphasis circuit.

FIG. 11 is a characteristic curve diagram showing a frequency amplitude characteristic of a de-enhanced circuit.

[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, 21 ...
… Pre-emphasis circuit, 22 …… De-emphasis circuit.

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

Claims (4)

[Claims] 1. An audio signal transmission apparatus for transmitting a digital audio signal through a predetermined transmission line, wherein the transmission line is formed to transmit 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 audio signal transmission device has the sampling frequency and a bit number greater than the bit number. A large number of digital audio signals are requantized to generate the transmission digital signal, and the transmission digital signal is transmitted through the transmission line, thereby transmitting the digital audio signal through the transmission line, and the digital audio signal is transmitted through the transmission line. When requantizing a signal, requantization noise is suppressed in the audible frequency band. , The audio signal transmitting apparatus characterized by noise the shaping. 2. The audio signal transmission device according to claim 1, wherein the energy distribution of the digital audio signal is detected, and the frequency characteristic of the noise shaping is switched based on the detection result. 3. When the transmission digital signal is transmitted through the transmission line, a frequency band higher than the audible frequency band of the transmission digital signal is emphasized and recorded on a recording medium through a pre-emphasis circuit. 3. The audio signal transmission device according to claim 1 or 2, wherein when the transmission digital signal recorded from a recording medium is reproduced, the transmission digital signal is output via a de-emphasis circuit. 4. The transmission line is a magnetic recording / reproducing device for recording the transmission digital signal of the sampling frequency and the bit number on a magnetic tape, and the sampling frequency is twice the audible frequency band. The audio signal transmission device according to claim 1, 2 or 3, wherein the frequency band has a frequency capable of recording and reproducing.