JPH06209297A - Transmitting method for audio signal - Google Patents

Abstract

PURPOSE:To make it possible to excellently perform the transmission/ recording/ reproduction of an audio signal with data amount by fixing the amplitude components and the phase components in every successive discrete frequency in each Fourier transform frame of an audio signal and transmitting the representative value. CONSTITUTION:By performing the calculation of the amplitude in the amplitude counting part 5A in an orthogonal coordinate spherical coordinate transform part 5 and the calculation of phases in a phase calculation part 5P, an amplitude spectrum and a phase spectrum are determined in every discrete frequency for the Fourier transform frame at every successive frame. The amplitude specturm is imparted to a band division part 6 and the phase spectrum is imparted to a band division part 7. In the band division parts 6, 7, the division of plural blocks is performed on each frequency axis. Next, in central value calculation parts 8, 9, the representative value of the amplitude components and the representative value of the phase components are calculated, they are outputted to a multiplexer 10 and they are transmitted to an output terminal 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acoustic signal transmitting method for compressing and transmitting an information amount of an acoustic signal.

[0002]

2. Description of the Related Art In recent years, an analog signal is often transmitted (or recorded / reproduced) as a digital signal, for example, a PCM (pulse code modulation) signal.
Since the PCM signal has a large amount of information, a wide transmission band is required for transmitting (or recording / reproducing) the PCM signal. Therefore, transmission devices (recording / reproducing devices) that perform signal processing of digital signals, and various other devices have conventionally been able to efficiently process digital signals with a small amount of information. As a high-efficiency coding method that enables efficient coding with a smaller amount of information, various types are used in which the signal is predicted and only the component (residual component) from the predicted value is recorded and transmitted. The high-efficiency coding method or the signal is extracted by performing some kind of transformation (generally orthogonal transformation) on the signal, and the characteristic part of the signal or the human visual or auditory sense has little change in the signal. The amount of information (the number of bits) for each sample is reduced by using the property that it is sensitive to changes in the part, but difficult to detect even if there is some error in the part where the signal changes drastically. You It is well known that various high-efficiency coding methods and the like have been conventionally proposed.

[0003]

However, in the conventional high-efficiency coding system, it has not been possible to compress the tone signal data at a high compression rate so that it can be reproduced in a high quality state. Therefore, the applicant company first compressed and transmitted the acoustic signal in the form of an amplitude component and a phase component by a high-efficiency encoding method of data using parameters expressed on the frequency axis, Various proposals have been made for various recording / reproducing systems (for example, Japanese Patent Application No. 4-322769).
No. specification, etc.),
The advent of an acoustic signal transmission method capable of transmitting and recording acoustic signals with a small amount of data was required.

[0004]

DISCLOSURE OF THE INVENTION The present invention discretely uses the same window function for a signal of each successive Fourier transform frame cut out from an acoustic signal so as to have a predetermined constant time length. Fourier transform, using the data for each of the same predetermined number of discrete frequencies obtained as a result of the Fourier transform for each Fourier transform frame described above, with the amplitude component for each successive discrete frequency in each Fourier transform frame described above. The phase component is obtained, and the amplitude component and the phase component for each discrete frequency of each Fourier transform frame are divided into a plurality of blocks on the frequency axis, and the number of lines is predetermined for each block. In addition to collecting the amplitude spectra of the above, a representative value of the amplitude component is obtained, and a predetermined number of phase spectra for each block described above are obtained. A representative value of the phase component is determined, and the representative value of the amplitude component and the representative value of the phase component are transmitted, and the acoustic signal is transmitted so as to have a predetermined constant time length. The signal of each successive Fourier transform frame cut out from the signal is subjected to discrete Fourier transform using the same window function, and the same predetermined number of discrete values obtained as a result of the Fourier transform for each Fourier transform frame described above. By using the data for each frequency, an amplitude component and a phase component for each discrete frequency in each Fourier transform frame described above are obtained, and an amplitude component and a phase component for each discrete frequency for each Fourier transform frame are obtained. Divide into a plurality of blocks on the frequency axis, find the arithmetic mean value of each of the above-mentioned predetermined number of amplitude spectra for each block, and then calculate the amplitude average value. And the representative value of the amplitude component and the representative value of the phase component, with one of them being the representative value of the phase component, for each of the predetermined number of phase spectra for each block described above. And a method of transmitting an acoustic signal adapted to transmit a value and a value.

[0005]

The signal of each successive Fourier transform frame cut out from the acoustic signal so as to have a predetermined constant time length is subjected to discrete Fourier transform using the same window function, and each Fourier transform described above is performed. By using the same predetermined number of data for each discrete frequency obtained as a result of the Fourier transform for each transform frame, the amplitude component and the phase component for each discrete frequency in each Fourier transform frame described above are obtained. The amplitude component and the phase component for each discrete frequency for each of the Fourier transform frames described above are divided into a plurality of blocks on the frequency axis, and a predetermined number of amplitude spectra are divided for each of the blocks. The arithmetic mean value is obtained and used as the representative value of the amplitude component. Further, for the predetermined number of phase spectra for each block, one of them is used as the representative value of the phase component. The representative value of the amplitude component and the representative value of the phase component are transmitted.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The concrete contents of the acoustic signal transmission method of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram showing a configuration example of an encoder used when implementing the method of transmitting an acoustic signal of the present invention, and FIG.
FIG. 3 is a block diagram showing a configuration example of a decoder used when implementing the acoustic signal transmission method of the present invention. In FIG. 1, reference numeral 1 denotes an input terminal of a digital audio signal to be recorded and transmitted, and the digital audio signal supplied to the input terminal 1 of the digital audio signal described above is overlapped by an overlap section 2. It is cut out so as to have a predetermined length of time in each state,
It is a sequential Fourier transform frame. Each of the Fourier transform frames described above is multiplied by a window function in the window function processing unit 3 so that each Fourier transform frame has a period having N (for example, N = 1024) sample points from the acoustic signal, and the joints of the respective frames are sequentially connected. It is cut out as one frame period in a sequence in which they overlap each other and are gently connected.
The above-mentioned Fourier transform frame for each frame is subjected to orthogonal transform in block 4 by, for example, discrete finite series Fourier transform (DFT) or fast Fourier transform (FFT). In the following description, the above orthogonal transformation is described as being performed by a fast Fourier transform (FFT).

When the FFT operation is performed for each Fourier transform frame for each frame, the number of data (sample number) in the Fourier transform frame for each frame is N, and the sampling frequency is fs. Then, the FFT operation result is obtained for each discrete frequency (total of N frequencies) for each frequency interval of f represented by f = fs / N. Real part amplitude and imaginary part for each specific frequency
(Imag) amplitude. The N discrete data for each discrete frequency obtained as a result of the FFT operation as described above is subjected to signal processing individually for each discrete frequency data.
The data of a specific discrete frequency, which is obtained as a result of the FT operation and is composed of a real number part and an imaginary number part for each of N discrete frequencies, is polar coordinate-transformed by the orthogonal coordinate → polar coordinate transforming part 5 to generate an amplitude term. After being separated into a phase term and a phase term, the amplitude calculation unit 5A calculates the amplitude according to the "Equation 1" and the phase calculation unit 5P calculates the phase according to the "Equation 2". For each Fourier transform frame of each of the above, for each discrete frequency described above,
An amplitude spectrum (amplitude component) and a phase spectrum (phase component) are obtained.

[0008]

[Equation 1]

[Equation 2]

By the way, as described above, the N real parts (Re
al) amplitude and N imaginary part (Imag) amplitudes, the same number of N real part (Real) amplitudes is 2
Appearing one by one, and N imaginary parts (Imag)
Since two amplitudes each having the same absolute value appear, the number of valid composite amplitude terms (Amp) is 1/2 of the total.
Since the number of effective phase terms is 1/2 of the total number, the number of FFT output data can be made equal to the number of FFT real input data.

As described above, the resolution on the frequency axis after the orthogonal transformation is f, where N is the number of data (number of samples) in the Fourier transform frame for each frame and fs is the sampling frequency. = Fs / N,
Now, assuming that the number of samples N = 1024 and the sampling frequency fs = 44100 Hz, the resolution in this case is f = fs / N = 44100/1024 = 43.07 Hz.
Becomes On the other hand, considering human hearing characteristics,
There is a difference between the resolution for low frequencies and the resolution for high frequencies, and human auditory characteristics in the audible frequency band have a fine resolution for low frequency sounds and a wide resolution for high frequency sounds. So-called
The critical bandwidth defines its resolution. Here, regarding the value of the resolution of 43.07 Hz described above, the numerical value of the resolution is a value that is too high for the high frequency, even if it is for the low frequency. From a viewpoint of data compression, it can be said that there is a great waste.

Therefore, in the method of transmitting an acoustic signal according to the present invention, the signals of each successive Fourier transform frame cut out from the acoustic signal so as to have a predetermined fixed time length are discretely distributed by using the same window function. Fourier transform, and using the same predetermined number of data for each discrete frequency obtained as a result of the Fourier transform for each Fourier transform frame, the amplitude for each successive discrete frequency in each Fourier transform frame described above. The component and the phase component are obtained, the amplitude component and the phase component for each discrete discrete frequency for each Fourier transform frame are divided into a plurality of blocks on the frequency axis, and each block is predetermined in advance. The representative values of the amplitude components are obtained by collecting the number of amplitude spectra, and a predetermined number of phase spectrums are set for each block. Defining a representative value of the phase components for Torr, so as to transmit a representative value of the representative values and the phase component of the amplitude component is had to be able to transmit the sound signal and the high efficiency compression.

That is, the amplitude calculation unit 5A in the rectangular coordinate → polar coordinate conversion unit 5 calculates the amplitude according to the "Formula 1" and the phase calculation unit 5P calculates the phase according to the "Formula 2". , The amplitude spectrum (amplitude component) in the amplitude spectrum (amplitude component) and the phase spectrum (phase component) obtained for each discrete frequency is sequentially divided into bands for each successive Fourier transform frame. The phase spectrum (phase component) is given to the band division unit 7. The amplitude spectrum (amplitude component) and the phase spectrum (phase component) are divided into predetermined frequency bands by the band division units 6 and 7, respectively, and divided into a plurality of blocks on the frequency axis.

Next, the amplitude component made into a block for each predetermined frequency band in the band division unit 6 is subjected to an arithmetic mean for a predetermined number of amplitude spectra in each block in the representative value calculation unit 8. , And outputs it to the multiplexer 10 as a representative value of the amplitude component,
In addition, the phase component which is made into a block for each predetermined frequency band in the band division unit 7 is a phase component which is one of the predetermined number of phase spectra in each block in the representative value calculation unit 9. The value is output to the multiplexer 10 as a representative value.
The representative value of the amplitude component and the representative value of the phase component are output terminal 11
Send to.

[0014]

[Table 1]

"Table 1" is a table showing an example of a concrete implementation of the acoustic signal transmission method of the present invention. In the specific example shown in "Table 1", each successive frame is For a Fourier transform frame, each discrete frequency f = fs
/ N, the amplitude spectrum (amplitude component) and the phase spectrum (phase component) obtained in each of the corresponding band division units 6 and 7, the block consisting of components belonging to the frequency band of 0 to 2.76 KHz, 2.76 KHz
A block composed of components belonging to the frequency band of 5.51 KHz, a block composed of components belonging to the frequency band of 5.51 KHz to 11.03 KHz, and 11.03 KHz
To 22.05 KHz, and each block is divided into blocks each having a predetermined number of spectra as shown in "Table 1". An example is shown in which a representative value is set for each of the collected spectra, so that the amplitude component and the phase component are transmitted by 160 representative values. In the example shown in "Table 1," the data amount can be compressed at such a ratio that the data amount originally corresponding to 512 spectra can be compressed to the data amount corresponding to 160 spectra.

In the specific example illustrated in "Table 1" above, 64 spectra can exist in the block of the lowest frequency band of 0 to 2.76 KHz. Regarding the block of the lowest frequency band, , The number of spectra to be combined into one in the block is 1, that is, all the spectra included in the block are respectively representative values, and 2.76 KHz to 5.51 KH
With respect to the 64 spectra existing in the block of the frequency band of z, the two spectra are grouped into one in the block, and the representative value is determined for each of the spectra, so that the frequency band of 2.76 KHz to 5.51 KHz is obtained. 32 representative values are set in the block of
With respect to 128 spectra existing in a block in the frequency band of 1 KHz to 11.03 KHz, by grouping four spectra each in the block and defining a representative value for each of them, the 5.51 KHz to
In the block of the frequency band of 11.03 KHz, 32 representative values are determined, and further, 11.03 KHz to 22.0.
Regarding the 256 spectra existing in the block of the frequency band of 5 KHz, the spectra of 8 lines each are grouped into one in the block, and the representative value is determined for each of the spectra, so that 11.03 KHz to 22.05 KHz.
In the block of the frequency band of, define 32 representative values,
160 representative values are defined for the entire frequency band of 0 to 22.05 KHz.

The calculation of the representative value in the representative value calculation unit 8 of the amplitude component is performed by calculating the arithmetic mean value of the amplitude spectrum values of a predetermined number for each block as described above, and the phase. The calculation of the representative value in the representative value calculation unit 9 of the component is performed by calculating a specific one of the phase spectra of a predetermined number for each block as described above, for example, of the phase spectra to be combined into one in the block. The representative value of the phase is determined according to a predetermined method of setting the representative value, such as setting the phase spectrum corresponding to the lowest frequency among them to the representative value. That is, since human hearing becomes less sensitive to the phase of an acoustic signal as the frequency becomes higher, in order to obtain a representative value for a plurality of phase spectra, a means such as calculating an arithmetic mean should be used. Instead of using it, one of the phase spectra may be arbitrarily selected and used as the representative value.

The data of the acoustic signal sent to the output terminal 11 in FIG.
It is sent from the transmission side to the reception side via the transmission line for decoding, or is recorded on a recording medium and then reproduced and then decoded. However, it is encoded by the encoder shown in FIG. The decoding operation for the data of the acoustic signal whose data amount is compressed by
It can be performed using a decoder having a configuration as illustrated in FIG. In FIG. 2, reference numeral 12 is an input terminal for the audio signal data to be decoded, and 13 is a demultiplexer. The data of the representative value of the amplitude component in the data of the audio signal to be decoded is supplied from the demultiplexer 13 to the restoration unit 14 of all the amplitude spectra from the representative value, and also to the target of decoding. The data of the representative value of the phase component in the data of the acoustic signal being supplied is supplied from the demultiplexer 13 to the restoration unit 15 of all the phase spectra from the representative value.

The above-described representative part 14 for all amplitude spectrum restorations and the representative value for all phase spectrum restorations 15 correspond to the number of spectra used to obtain each representative value and the corresponding number of times. However, the restoration operation is performed by repeatedly outputting the respective representative values and supplying the representative values to the polar coordinate → rectangular coordinate conversion unit 16. The polar-coordinate-to-rectangular-coordinate conversion unit 16 calculates the real part amplitude and the imaginary part amplitude at the specific discrete frequency based on the amplitude component data and the phase component data at the specific discrete frequency supplied thereto. And supplies it to the inverse FFT calculator 17. The inverse FFT calculator 17 restores the original acoustic signal data and supplies it to the window function processor 18. The data of the acoustic signal subjected to the window function processing by the window function processing section 18 is overlap-added by the overlap adding section 19 and sent to the output terminal 20.

In implementing the acoustic signal transmission method of the present invention, a method of data compression using masking may be combined, or the data compression rate may be further improved. Alternatively, the compression method based on the orthogonal transformation and the prediction proposed by the applicant company may be combined and implemented. Further, in carrying out the method for transmitting an acoustic signal of the present invention, the amplitude component and the phase component for each discrete frequency for each Fourier transform frame are divided into a plurality of blocks on the frequency axis. The size, the number of spectra to be collected as a representative value, and the like may be adaptively changed for each Fourier transform frame, but as such an embodiment, the acoustic signal transmission method of the present invention is implemented. When
The information set corresponding to each item shown in "Table 1" also needs to be added to data and transmitted.

[0021]

As is apparent from the above description in detail, the method of transmitting an acoustic signal of the present invention is such that each of the sequential Fourier signals cut out from the acoustic signal so as to have a predetermined fixed time length. The signal of the transform frame, subjected to discrete Fourier transform using the same window function, using the same predetermined number of discrete frequency data obtained as a result of the Fourier transform for each Fourier transform frame described above, Obtaining an amplitude component and a phase component for each discrete frequency in each Fourier transform frame described above, a plurality of amplitude components and phase components for each discrete frequency for each Fourier transform frame on the frequency axis. Divided into blocks, the arithmetic mean value of each of the predetermined number of amplitude spectra for each of the blocks described above is obtained, and it is used as the representative value of the amplitude component. Also, with respect to a predetermined number of phase spectra for each block, one of them is used as the representative value of the phase component, and the representative value of the amplitude component and the representative value of the phase component are transmitted. Therefore, according to the audio signal transmission method of the present invention, even if the data is compressed at a high compression rate, the data of the musical tone signal can be reproduced in a high quality state. As compared with the above, the transmission and recording / reproduction of the acoustic signal can be favorably performed with a smaller amount of data, and the conventional problems already described by the present invention can be favorably solved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of an encoder used when implementing an acoustic signal transmission method of the present invention.

FIG. 2 is a block diagram showing a configuration example of a decoder used when implementing the acoustic signal transmission method of the present invention.

[Explanation of Codes] 1 ... Input terminal of digital audio signal targeted for recording and transmission, 2 ... Overlap portion, 3 ... Window function processing portion,
5 ... Cartesian coordinate → polar coordinate conversion unit, 5A ... Amplitude calculation unit, 5P
... phase calculation section, 6, 7 ... band division section, 8, 9 ... representative value calculation section, 10 ... multiplexer, 12 ... audio signal data input terminal to be decoded, 13 ... de-multiplexer, 14 ... reconstruction part of all amplitude spectra from the representative value, 15 ... reconstruction part of all phase spectra from the representative value, 16 ... polar coordinate → rectangular coordinate conversion part, 17 ... inverse FFT operation part, 18 ... window function processing part, 19 ... Overlap adder, 20 ... output terminal,

Claims (2)

[Claims] 1. The Fourier transform is performed discretely by using the same window function on a signal of each successive Fourier transform frame cut out from an acoustic signal so as to have a predetermined fixed time length, and each Fourier transform described above. Using the same predetermined number of data for each discrete frequency obtained as a result of the Fourier transform for each transform frame, to obtain the amplitude component and the phase component for each successive discrete frequency in each Fourier transform frame described above, The amplitude component and the phase component for each discrete frequency of the Fourier transform frame are divided into a plurality of blocks on the frequency axis, and a predetermined number of amplitude spectra are collectively collected for each of the above-mentioned blocks. While obtaining the representative value of, the representative value of the phase component is determined for each of the predetermined number of phase spectra for each block described above, A method of transmitting an acoustic signal, wherein the representative value of the amplitude component and the representative value of the phase component are transmitted. 2. The Fourier transform is discretely Fourier-transformed using the same window function to the signal of each successive Fourier transform frame cut out from the acoustic signal so as to have a predetermined fixed time length, and each Fourier transform described above. Using the same predetermined number of data for each discrete frequency obtained as a result of the Fourier transform for each transform frame, to obtain the amplitude component and the phase component for each successive discrete frequency in each Fourier transform frame described above, The amplitude component and the phase component for each discrete frequency for the Fourier transform frame are divided into a plurality of blocks on the frequency axis, and the arithmetic mean value of each of the predetermined number of amplitude spectra for each block described above. Then, the value is used as the representative value of the amplitude component, and the number of phase spectra is determined for each block described above. A method of transmitting an acoustic signal, wherein one of the two is used as a representative value of the phase component, and the representative value of the amplitude component and the representative value of the phase component are transmitted.