JPH07311593A - Muting device of subband dividing-encoded audio decoder - Google Patents

Abstract

PURPOSE:To obtain a muting device for a subband dividing-encoded audio decoder which performs muting without increasing a memory and a multiplier. CONSTITUTION:The subband synthesizer is provided with a multiplier 13, which multiplies an orthogonal transformer 11 of a decoder, window coefficients of a window coefficient ROM12, and orthogonally transformed values, a memory 16 which stores the data equivalent to a window length 2MN (that are 2M times a subband dividing number N where M is an integer), an adding means 17 which performs a cumulative adding while shifting every N samples when the outputs of the multiplier 13 are X0<t>, X1<t>...X2MN-1<t> and the data in the memory are Y0<t-1>, Y1<t-1>...Y2MN-1<t-1> and returns results Y0<t>, Y1<t>...Y2MN-1<t> to the memory 16 and a buffer memory 18 which latches first N (subband dividing number) sample data of the adding results and a selector 15 which switches the data inputted to the means 17 to '0'.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a muting device for a subband division coding audio decoder.

[0002]

2. Description of the Related Art In recent years, skillfully utilizing human auditory characteristics,
The field of MPEG audio broadcasting, communication, and storage media internationally standardized by ISO / IEC as an encoding technology in which audio quality deterioration is hardly detected in hearing even if the audio signal is compressed to about 1/6 to 1/8. Is being considered for use. Generally, a medium which receives and stores an encoded bit stream requires a decoder to reproduce an audio signal. Here, in a general coding method, since coding is performed in frame units, if an error occurs in the bit stream, it becomes necessary to mute the entire frame.

There are various types of muting methods such as zero mute, zero cross mute, and soft mute, but soft mute that allows smooth muting without abnormal noise at the start and end of muting is important. Yes, muting assumes soft mute here. The muting device of this sub-band division encoding audio decoder will be described by taking as an example the case where MPEG audio is used as the encoding method. For MPEG audio, ISO / IEC /
JTC1 / SC2 "Information Technology-Coding of
Moving Pictures and Associated Audio for Digital
Storage Media up to about 1.5Mbit / s.Part3: Coding o
f audio information ”.

FIG. 10 is a block diagram of a muting device of a conventional sub-band division coding audio decoder. In the figure, 1 is a sync detector for synchronizing the input bit stream, 2 is a frame unpacking circuit for unpacking the bit stream, and 3 is a CRC.
A detector, 4 is a bit allocation decoder that decodes the bit allocation unpacked by the frame unpacking circuit 2, 5 is a scale factor decoder that also decodes the unpacked scale factor, and 6 is the same unpacked sample. An inverse quantizer for the sample, which calculates an inverse quantization value by performing an operation C × (sample data + D) from the coefficients C and D based on the quantization level of the data, and 7 is an inverse quantizer obtained by the inverse quantizer 6. An inverse normalizer that obtains an inverse normalization value by multiplying the normalized value by a scale factor, 8 is a subband synthesizer that performs subband synthesis on the inverse normalization value to calculate an audio output, and 41 is the previous one. A frame memory for storing audio data of frames, 42 is a frame memory 4
A switch circuit for switching whether to send the data in 1 to the multiplier for muting 44 or to the selector 45 according to the mute signal, 43 is a mute coefficient ROM having a muting coefficient, and 44 is a mute coefficient and a frame memory. A multiplier for multiplying data, and 45 is a selector for switching between outputting the output from the muting multiplier 44 or outputting the data in the frame memory as an output according to a mute signal.

Next, the operation of the conventional example will be described. The synchronization of the input bit stream is detected by the synchronization detector 1. If synchronized, the frame unpacking circuit 2 extracts the header information,
Each information required for decoding such as presence / absence of CRC, bit rate, sampling frequency, channel mode, etc. is set. Also, the audio data is separated into bit allocation information, scale factor information, and sample data. If there is a CRC check bit, the CRC detector 3 checks for an error.

Next, the bit allocation information separated by the frame unpacking circuit 2 is input to a bit allocation decoder 4 to obtain a quantization level.
The scale factor information is the scale factor decoder 5
A scale factor value is obtained that is multiplied by the inverse quantized value of the associated sample input to. The sample is input to the sample dequantizer 6 and the bit allocation decoder 4 is input.
The coefficients C and D are selected based on the quantization level obtained by, and the inverse quantized value is obtained by the operation of C × (sample data + D). Next, the dequantized value is input to the denormalizer 7 and multiplied by the scale factor obtained by the scale factor decoder 5 to obtain the dequantized value. The dequantized value is subband-combined by the subband synthesizer 8 and decoded as an audio signal.

Next, when the mute signal is detected, the switch circuit 42 sends the audio output to the multiplier 44. In the multiplier 44, the audio output is multiplied by the mute coefficient such as the linear function shown in FIG. 11 or the logarithmic function shown in FIG. 12 in the mute coefficient ROM 43, and the linear mute of FIG. 13 and the logarithm of FIG. 14 are multiplied. Obtain the muting output as shown in Mute. Further, as the output signal, the mute output from the multiplier 44 is selected by the selector 45. In order to prevent abnormal noise from being generated at the beginning of muting by this method, it is necessary to perform muting in the frame before the mute signal is issued. Therefore, it is necessary to hold the data of one frame before in the frame memory 41.

[0008]

As described above, in the muting device in the conventional sub-band division coding audio decoder, the memory 41 for holding the decoded audio signal of the previous frame for a predetermined period is used for muting. It was necessary, and there was a problem that the H / W scale increased.

The present invention has been made in order to solve the above problems, and it is a sub that can perform a soft muting operation without newly adding a memory for holding a decoded audio signal. It is an object to obtain a muting device for a band division coded audio decoder.

[0010]

According to another aspect of the present invention, there is provided a muting device for a sub-band division coding audio decoder according to the present invention.
M, a multiplier that multiplies the window coefficient and the orthogonal transformation value, and "0"
A generator, and a selector for switching from the multiplication result by the multiplier to the output of the “0” generator when a mute signal is detected,
Window length 2MN (2M of subband division number N (M: integer)
And a memory for storing the same amount of data, and outputs from the selector are X ₀ ^t , X ₁ ^t , ... X _2MN-1 ^t, and the data in the memory is Y ₀ ^t-1 , Y ₁ ^t-1 , ... Y
When the ^{_{2MN-1 t-1,}} performs addition, as shown in the following equation, and adding means for returning the result Y ₀ ^t, Y ₁ ^t, the ···· Y _2MN-1 ^t in the memory, It is provided with a buffer memory for latching the data of the first N (subband division number) samples of the addition result. ^{_{Y i t = Y i + N}} t-1 + X i t (i = 0 ··· 2MN-1-N) Y i t = X i t (i = 2MN-N ··· 2MN-1)

According to a second aspect of the present invention, there is provided a muting device for a sub-band division coding audio decoder, which comprises a sub-band synthesizer, an orthogonal transformer, a window coefficient ROM, and a multiplier for multiplying the window coefficient and the orthogonal transform value. A "0" generator, a selector for switching from the multiplication result by the multiplier to the output of the "0" generator when a mute signal is detected, and a window length 2MN (2M (M: integer) times the subband division number N). ) Of the memory to store the data and the output from the selector is X ₀ ^t , X ₁
^t, and ···· X _2MN-1 ^t, the data in the memory when ^{_{Y 0 t-1, Y 1}} t-1, and ^{_{···· Y 2MN-1 t-1}} , the following equation Addition means for performing addition as shown and _{returning the} results Y ₀ ^t , Y ₁ ^t , ... Y _2MN-1 ^t to the memory, and the first N (subband division number) samples of the addition result A buffer memory for latching data, a controller and a switch for stopping the input from the memory to the adding means for one cycle (2MN) after detection of the mute release signal are provided. ^{_{Y i t = Y i + N}} t-1 + X i t (i = 0 ··· 2MN-1-N) Y i t = X i t (i = 2MN-N ··· 2MN-1)

According to a third aspect of the present invention, there is provided a muting device for a sub-band division coding audio decoder, comprising: a sub-band synthesizer, an orthogonal transformer, a window coefficient ROM, and a first multiplier for multiplying the window coefficient by the orthogonal transform value. And a “0” generator,
When a mute signal is detected, a selector for switching from the multiplication result by the first multiplier to the output of the "0" generator and data for a window length 2MN (2M (M: integer) times the subband division number N) are stored. , And the output from the selector is X ₀ ^t , X ₁ ^t , ... X _2MN-1 ^t, and the data in the memory is Y ₀ ^t-1 , Y ₁ ^t-1 ,.・ Y _2MN-1 ^t-1
In such a case, addition as shown in the following equation is performed, and the result Y ₀ ^t , Y ₁ ^t , ... Y _2MN-1 ^t is _returned to the memory, and the first N of the addition results. (Number of subband divisions) A buffer memory for latching sample data and a switch for sending the output of the buffer memory to the second multiplier when a mute signal is detected, a mute output correction coefficient ROM, a correction coefficient, and an output value from the buffer memory. Second to multiply
And a second selector for switching the output values of the multiplier and the decoder to the output from the second multiplier. ^{_{Y i t = Y i + N}} t-1 + X i t (i = 0 ··· 2MN-1-N) Y i t = X i t (i = 2MN-N ··· 2MN-1)

According to a fourth aspect of the present invention, there is provided a muting device for a sub-band division coding audio decoder, comprising: a sub-band synthesizer, an orthogonal transformer, a window coefficient ROM, and a multiplier for multiplying the window coefficient and the orthogonal transform value. A "0" generator, a selector for switching from the multiplication result by the multiplier to the output of the "0" generator when a mute signal is detected, and a window length 2MN (2M (M: integer) times the subband division number N). ) Of the memory to store the data and the output from the selector is X ₀ ^t , X ₁
^t, and ···· X _2MN-1 ^t, the data in the memory when ^{_{Y 0 t-1, Y 1}} t-1, and ^{_{···· Y 2MN-1 t-1}} , the following equation Addition means for performing addition as shown and _{returning the} results Y ₀ ^t , Y ₁ ^t , ... Y _2MN-1 ^t to the memory, and the first N (subband division number) samples of the addition result In addition to a buffer memory for latching data, a means for adding the sync error detection signal output from the sync detector and the CRC error detection signal output from the CRC detector to the mute signal is provided. ^{_{Y i t = Y i + N}} t-1 + X i t (i = 0 ··· 2MN-1-N) Y i t = X i t (i = 2MN-N ··· 2MN-1)

[0014]

An orthogonal transformer in a muting device of a subband division coding audio decoder according to any one of claims 1 to 4 transforms subband data into time domain data,
The first multiplier performs windowing on the orthogonal transformation value, and the adding means and the memory obtain the subband composite value by accumulating and adding the windowed data for a predetermined period.

The "0" generator and the selector in the muting device of the subband division coding audio decoder according to the first to fourth aspects of the present invention, when the mute signal is detected,
The value added by the adding means is set to "0" from the new windowed data.
The cumulative addition data is attenuated by switching to, and the value added to the adding means again after the mute signal is released is switched to new windowing data. It is possible to do.

In the switch and controller according to the second aspect of the present invention, the value in the memory is not added to the input of the adding means for one cycle (2MN) after releasing the mute signal, so that 0 is newly added after releasing the mute. It is possible to perform soft muting from.

The switch, the mute output correction coefficient multiplier and the second selector according to the third aspect of the present invention, when the mute signal is detected, multiplies the mute output in the buffer memory by the mute output correction coefficient and mutes the corrected output. By outputting as an output, soft mute can be performed.

A frame in which a sync error and a CRC error are generated by a means for adding the sync error detection signal output from the sync detector and the CRC error signal output from the CRC detector to the mute signal. It is possible to mute the abnormal noise.

[0019]

【Example】

Example 1. Hereinafter, the present invention will be described with reference to the drawings. Figure 1
10 is a block configuration diagram of an MPEG audio decoding device according to Embodiment 1 of the present invention, in which the same reference numerals as in FIG. 10 denote the same or corresponding portions, and 10 is an OR gate,
A mute signal, a sync error detection signal, and a CRC error detection signal are input, and the output is a subband synthesizer 8
Given as a mute signal.

FIG. 2 is a block diagram of the subband synthesizer and the muting device of the decoder according to the first embodiment. In the figure, 11 is an orthogonal transformer that transforms subband samples into time domain data, 12 is a ROM having a window coefficient of a window length of 512, 13 is a multiplier that multiplies the orthogonal transform value by the window coefficient, and 14 is " 0 "generator, 15 is a selector for switching to the data from the" 0 "generator when a mute signal is detected, 16 is a ring memory for holding 512-word data, 17 is the output from the selector 15 X ₀ ^t , X ₁
^t, and · · · · X ₅₁₁ ^t, the data in the ring memory ^{_{Y 0 t-1, Y 1}} t-1, when a ^{_{···· Y 511 t-1, Y}} i t = Y i ^{_{+32 t-1 + X i t}} (i = 0 ··· 479) performs a ^{_{Y i t = X i t (}} i = 480 ··· 511) consisting of the addition, the result ^{_{Y 0 t, Y 1 t,}} ·· ..Y
₅₁₁ ^t is an adding means for returning to the ring memory, and 18 is a 32-word buffer memory for latching the first 32 samples of the addition result of the adding means 17.

FIG. 3 is a muting waveform output by the muting device of the subband division coding audio decoder according to the first embodiment of the present invention.

FIG. 4 is another block diagram of the subband synthesizer and the muting device of the decoder according to the first embodiment. In the figure, 11 to 18 are the same as the circuits shown in FIG. 2, 21 is a switch circuit for turning on / off the input from the ring memory to the adding means, 22
Is a control circuit for controlling the switch so that the input from the ring memory to the adding means is stopped for one cycle after the mute signal is detected.

Next, the operation of the first embodiment will be described. M
The sync detector 1 detects the sync of the MPEG audio bit stream input to the PEG audio decoding device. If synchronized, the frame unpacking circuit 2 extracts the header information,
Presence / absence of CRC, bit rate, sampling frequency, presence / absence of padding, channel mode and the like are set. Also, the audio data is bit allocation information,
Separated into scale factor information and sample data.
If there is a CRC check bit, the CRC detector 3 checks the error.

Next, the bit allocation information separated by the frame unpacking circuit 2 is input to the bit allocation decoder 4, and the quantization level is obtained. The scale factor information is input to the scale factor decoder 5 to obtain a scale factor value by which the inverse quantization value of the relevant sample is multiplied. sample,
The coefficients C and D are selected based on the quantization level obtained by the sample dequantizer 6 and obtained by the bit allocation decoder 4, and C (sample data + D) is selected.
The inverse quantized value is obtained by the following operation. Next, the dequantized value is input to the denormalizer 7 and is multiplied by the scale factor obtained by the scale factor decoder 5 to obtain the denormalized value. The inverse quantized value is the subband synthesizer 8
At, sub-band synthesis is performed and decoded as an audio signal.

The sync error detection signal when the sync detector 1 detects the error and the CRC error detection signal when the CRC detector 3 detects the error are muted through the OR gate 10. Added to
It is input to the muting device of the subband synthesizer 8.

Next, the operation of the subband synthesizer and the muting device having the configuration shown in FIG. 2 will be described. Subband synthesis is ΣN × S according to ISO / IEC standards.
(N: cosine coefficient, S: subband sample) orthogonal transformation, D × U (D: window coefficient, U: orthogonal transformation value) windowing, and ΣW (W = D × U) cumulative addition . Therefore, in order to realize the subband synthesizer, it is necessary to perform the following operations in each circuit shown in FIG. 2 and each circuit. The 32 subband samples obtained by the inverse normalizer 7 are multiplied by the orthogonal transformation matrix in the orthogonal transformer 11 to obtain an orthogonal transformation value of 512 samples. Next, in the multiplier 13, the window coefficient R is applied to the orthogonal transformation value.
The window coefficient in the OM 12 is multiplied and input to the selector 15. Then, in the adding means 17, the outputs X ₀ ^t , X ₁ ^t , ... X _{51 1} ^t from the selector 15 and the data Y ₀ ^t-1 , Y ₁ ^t-1 , in the 512 word ring memory 16,・
... Y ₅₁₁ ^t-1 is added according to the following equation, and as a result Y _{0
^{t, Y 1 t, ···· Y}} 511 t is recorded in the ring memory 16 again. ^{_{Y i t = Y i + 32}} t-1 + X i t (i = 0 ··· 479) Y i t = X i t (i = 480 ··· 511) In addition, among the addition result of the adding means 17 The first 32 samples are latched in the 32 word buffer memory 18 and become output data.

In the muting device of the sub-band division coding audio decoder as described above, when the muting signal is input, the selector 15 inputs the input to the adding means 17 of the sub-band synthesizer to a "0" generator. Switch to the output from 14. As a result, the output gradually attenuates as shown in FIG. 3 and becomes 0 after 512 samples, and soft muting is performed.

As described above, when the muting signal is detected, the data input to the adding means of the subband synthesizer is switched to the output from the "0" generator to obtain the soft muting output. Soft muting is possible without increasing the memory and multiplier for muting.

Next, when the muting signal cancellation is detected, the selector 15 switches the input to the adding means 17 again to the multiplication result of the multiplier 13. According to this method, the output is gradually increased as shown in FIG. 3, and is restored to the correct output value after 512 samples.

As described above, when the muting signal cancellation is detected, the input to the adding means of the subband synthesizer is switched to the multiplication result again, so that it is possible to increase the number of muting memories and multipliers. Muting can be canceled.

Further, by adding the sync error detection signal obtained by the sync detector 1 and the CRC error detection signal obtained by the CRC detector 3 as the muting signal, no abnormal noise is generated in the frame in which the error occurs. Is possible.

Next, as another method, the operation of the muting device having the configuration shown in FIG. 4 will be described. Subband samples input to the subband synthesizer are 11 to
In the circuit of 18, the muting operation is performed by the same operation as in the example of FIG. However, when the switch control circuit 22 detects the mute signal cancellation, the switch circuit 21 is turned off so as to stop the input from the ring memory 16 to the adding means 17 for one cycle, so that the output once becomes 0 after the muting cancellation and the output starts from 0. Gradually increasing, 5
The correct output value is restored after 12 samples.

As described above, when the muting signal is released,
Since the input from the ring memory 16 to the adding means 17 is cut off, the muting can be canceled without increasing the memory for muting and the multiplier.

Example 2. FIG. 5 is a block diagram of a subband synthesizer and a muting device of a subband division coding audio decoder according to the second embodiment of the present invention.
In the figure, the same reference numerals as those in FIG. 2 and FIG. 4 respectively denote the same or corresponding portions, and 31 indicates the mute output after the sub-band synthesis in the 32-word buffer memory 18 to the input of the multiplier 33 when the mute signal is detected. A switch circuit for switching, 32 is a mute output correction coefficient ROM having a coefficient for correcting the mute output after subband synthesis, and 33 is a mute output correction coefficient for correcting the mute output after subband synthesis to a predetermined mute output. ROM3
A multiplier that multiplies the correction coefficient in 2 and a selector 34 that switches the output to the corrected mute value from the multiplier 33 when a mute signal is detected.

FIG. 6 shows a sub-band synthesizer of a decoder and a window coefficient ROM 1 of a muting device according to the first and second embodiments.
It is a figure which shows the window coefficient in 2.

FIG. 7 shows the attenuation coefficient of the muting waveform in the subband synthesizer of the decoder and the muting device according to the first embodiment. The value obtained by adding up to 16 times while shifting the window coefficient of FIG. It is shown.

FIG. 8 shows an example of the correction coefficient in the mute output correction coefficient ROM 32 in the subband synthesizer of the decoder and the muting device according to the second embodiment. The mute waveform of the first embodiment as shown in FIG. FIG. 14 is a diagram showing coefficients for correcting a linear decrease mute waveform as shown in FIG. 13.

FIG. 9 shows another example of the correction coefficient in the mute output correction coefficient ROM 32 in the sub-band synthesizer of the decoder and the muting device according to the second embodiment. The mute of the first embodiment as shown in FIG. Figure 14 shows the waveform
It shows the coefficient for correcting the logarithmic decrease mute waveform as shown in FIG.

Next, the operation of the second embodiment will be described. The subband samples are subband-combined by the circuits 11 to 18, and the muting output is obtained by adding the data from the "0" generator when the mute signal is detected. This muting waveform becomes slightly larger in amplitude than the original waveform before being attenuated as shown in FIG. In order to convert this waveform into a linear decreasing waveform or a logarithmic decreasing waveform as shown in the conventional example, the 32-word buffer memory 1 is switched by switching the switch 31 when the mute signal is detected.
The data in 8 is added to the input of the multiplier 33, and the coefficient in the mute output correction coefficient ROM 32 is multiplied. Then, the selector 34 switches the output during mute to the multiplication result.

Here, the buffer memory 18 at the time of mute
The following can be said about the output waveform from the. Since the value added cumulatively by the adding means 17 while shifting by 32 samples is held in the 512-word ring memory, the oldest 32 samples are cumulatively added 16 times, and thereafter, every 32 samples have 15 values. Cumulative addition data for one batch, 14 batches ... 1 batch. Since "0" is added by the selector 15 after the mute signal is detected, it can be considered that the data in the ring memory is directly output as the output of the adding means. Therefore, it is considered that the data in the ring memory is multiplied by the cumulative addition value of the window coefficient. The cumulative addition value of the window coefficient is as shown in FIG. 7, which matches the shape of the envelope of the mute waveform in FIG. Therefore, the correction coefficient necessary for correcting the waveform having the attenuation as shown in FIG. 7 to the muting output as shown in FIGS. 13 and 14 of the conventional example is the window coefficient shown in FIG. When the cumulative addition value is C _i and the mute coefficient shown in FIGS. 11 and 12 is D _i , correction coefficient = D _i / C _i is obtained. FIG. 8 and FIG. 9 show correction coefficients when performing the straight line decreasing muting and the logarithmic decreasing muting, respectively.

As described above, when the muting signal is detected, the data input to the adding means is switched to the output from the "0" generator, and the output value is multiplied by the correction coefficient. Since it is configured to obtain the soft muting output of, the predetermined soft muting can be performed without increasing the memory for muting.

[0042]

According to the first aspect of the present invention, when the muting signal is detected, the data input to the adding means is switched to "0", and when the muting signal cancellation is detected, the addition means is operated. By returning the input to the multiplication result again, the soft muting operation can be performed without increasing the memory and the multiplier.

According to the second aspect of the present invention, when the muting signal is detected, the data input to the adding means is switched to "0", and when the muting signal cancellation is detected, the input to the adding means. Is returned to the multiplication result and the data in the memory is not added to the input of the cumulative addition for one cycle, which has the effect of enabling the soft muting operation without increasing the memory and the multiplier.

According to the third aspect of the present invention, when the muting signal is detected, the data input to the adding means of the subband synthesizer is switched to "0", and the output data is multiplied by the correction coefficient. This has the effect of enabling predetermined soft muting without increasing memory.

According to the invention of claim 4, by further adding the synchronization error detection signal and the CRC error detection signal to the muting signal, there is an effect that no abnormal noise is generated at the time of error.

[Brief description of drawings]

FIG. 1 is a block diagram of an MPEG audio decoding device according to a first embodiment of the present invention.

FIG. 2 is a block configuration diagram of a subband synthesizer and a muting device of a decoder according to the first embodiment.

FIG. 3 is a muting waveform output by the muting device of the subband division coding audio decoder according to the first embodiment.

FIG. 4 is another block diagram of the subband synthesizer of the decoder and the muting device according to the first embodiment.

FIG. 5 is a block configuration diagram of a subband synthesizer and a muting device of a subband division encoding audio decoder according to Embodiment 2 of the present invention.

FIG. 6 is a diagram showing window coefficients in a window coefficient ROM 12 of the subband synthesizer of the decoder and the muting device according to the first and second embodiments.

FIG. 7 is an attenuation coefficient of a muting waveform in the subband synthesizer of the decoder and the muting device according to the first embodiment.

FIG. 8 is a mute output correction coefficient R in the subband synthesizer and the muting device of the decoder according to the second embodiment.
It is an example of a correction coefficient in OM32.

FIG. 9 is a mute output correction coefficient R in the subband synthesizer and the muting device of the decoder according to the second embodiment.
It is another example of the correction coefficient in the OM32.

FIG. 10 is a block diagram of a muting device of a conventional sub-band division coding audio decoder.

FIG. 11: Mute coefficient ROM in a muting device of a conventional sub-band division encoding audio decoder
It is a figure which shows an example of the coefficient data in.

FIG. 12 is a mute coefficient ROM in a muting device of a conventional subband division coding audio decoder.
It is a figure which shows another example of the coefficient data in.

FIG. 13 is a diagram showing an example of a muting output in a muting device of a conventional subband division encoding audio decoder.

FIG. 14 is a diagram showing another example of a muting output in a muting device of a conventional subband division encoding audio decoder.

[Explanation of symbols]

1 sync detector, 2 frame unpacking circuit, 3
CRC detector, 4-bit allocation decoder, 5
Scale factor decoder, 6 inverse quantizer, 7 inverse normalizer, 8 subband synthesizer, 10 OR gate, 11
Orthogonal transformer, 12 512 window coefficient ROM, 13 multiplier, 14 “0” generator, 15 selector, 16 ring memory, 17 cumulative addition means, 18 32 word buffer memory, 21 switch circuit, 22 switch control circuit, 31 switch Circuit, 32 mute output correction coefficient ROM, 33 correction coefficient multiplier, 34 output selector.

Claims (4)

[Claims] 1. A decoder for inputting a bit stream coded by a sub-band division coding method and reproducing a digital audio signal after decoding by sub-band synthesis, wherein the sub-band synthesizer has an orthogonal transformer and a window coefficient. RO
A multiplier that multiplies M, the window coefficient, and the orthogonal transformation value, a "0" generator, a selector that switches between the multiplication result of the multiplier and the output of the "0" generator, and a window length 2MN (the number of subband divisions). The output from the memory and the selector for storing 2M (M: integer) times N data is X ₀ ^t , X ₁ ^t , ...
... and X _2MN-1 ^t, the data in the memory Y ₀ ^t-1,
When Y ₁ ^t-1 , ..., Y _2MN-1 ^t-1 , addition as shown in the following formula is performed, and as a result, Y ₀ ^t , Y ₁ ^t , ...
_..Addition means for _returning Y _2MN-1 ^t to the memory and a buffer memory for latching the data of the first N (subband division number) samples of the addition result, and when the mute signal is detected, the selector causes the addition means to be added Enter "0"
A muting device for a sub-band division coding audio decoder, which is characterized by performing soft muting by switching to. ^{_{Y i t = Y i + N}} t-1 + X i t (i = 0 ··· 2MN-1-N) Y i t = X i t (i = 2MN-N ··· 2MN-1) 2. A decoder for inputting a bit stream coded by a sub-band division coding method and reproducing a digital audio signal after decoding by sub-band synthesis, wherein the sub-band synthesizer has an orthogonal transformer and a window coefficient. RO
A multiplier that multiplies M, the window coefficient, and the orthogonal transformation value, a "0" generator, a selector that switches between the multiplication result of the multiplier and the output of the "0" generator, and a window length 2MN (the number of subband divisions). The output from the memory and the selector for storing 2M (M: integer) times N data is X ₀ ^t , X ₁ ^t , ...
... and X _2MN-1 ^t, the data in the memory Y ₀ ^t-1,
When Y ₁ ^t-1 , ..., Y _2MN-1 ^t-1 , addition as shown in the following formula is performed, and as a result, Y ₀ ^t , Y ₁ ^t , ...
_..Adding means for _returning Y _2MN-1 ^t to the memory, a buffer memory for latching data of the first N (subband division number) samples of the addition result, and data in the memory to the input of the adding means A switch and a controller for switching whether the mute signal is detected, the selector switches the input to the adding means to "0" when the mute signal is detected, and the switch and the controller store the memory for one cycle (2MN) after detecting the mute signal cancellation. A muting device for a sub-band division coding audio decoder, characterized in that soft muting is performed by not adding the data of 1. to the input of the adding means. ^{_{Y i t = Y i + N}} t-1 + X i t (i = 0 ··· 2MN-1-N) Y i t = X i t (i = 2MN-N ··· 2MN-1) 3. A decoder for inputting a bit stream coded by a sub-band division coding method and reproducing a digital audio signal after decoding by sub-band synthesis, wherein the sub-band synthesizer has an orthogonal transformer and a window coefficient. RO
A first multiplier for multiplying M, the window coefficient and the orthogonal transform value;
A "0" generator and a first selector for switching between the multiplication result of the first multiplier and the output of the "0"generator;
Window length 2MN (2M of subband division number N (M: integer)
The output from the first selector and the memory for storing the data) is X ₀ ^t , X ₁ ^t , ... X _2MN-1 ^t ,
The data in the memory is stored in Y ₀ ^t-1 , Y ₁ ^t-1 , ...
When the ^{_{2MN-1 t-1,}} performs addition, as shown in the following equation, and adding means for returning the result Y ₀ ^t, Y ₁ ^t, the ···· Y _2MN-1 ^t in the memory, A buffer memory for latching the data of the first N (subband division number) samples of the addition result and a switch for sending the output of the buffer memory to the second multiplier, the mute output correction coefficient ROM, the correction coefficient, and the output from the buffer memory. A second multiplier for multiplying a value and a second selector for selecting an output from the second multiplier or an output from the buffer memory are provided, and when the mute signal is detected, the first selector transfers the addition means to the addition means. Is switched to "0" and the output of the buffer memory is input to the second multiplier by the switch to multiply the mute output correction coefficient to perform a predetermined soft muting. Subband division encoded audio decoder muting device that. ^{_{Y i t = Y i + N}} t-1 + X i t (i = 0 ··· 2MN-1-N) Y i t = X i t (i = 2MN-N ··· 2MN-1) 4. A decoder for inputting a bit stream coded by a sub-band division coding method and reproducing a digital audio signal after decoding by sub-band synthesis, wherein the sub-band synthesizer has an orthogonal transformer and a window coefficient. RO
A multiplier that multiplies M, the window coefficient, and the orthogonal transformation value, a "0" generator, a selector that switches between the multiplication result of the multiplier and the output of the "0" generator, and a window length 2MN (the number of subband divisions). The output from the memory and the selector for storing 2M (M: integer) times N data is X ₀ ^t , X ₁ ^t , ...
... and X _2MN-1 ^t, the data in the memory Y ₀ ^t-1,
When Y ₁ ^t-1 , ..., Y _2MN-1 ^t-1 , addition as shown in the following formula is performed, and as a result, Y ₀ ^t , Y ₁ ^t , ...
_..Addition means for _returning Y _2MN-1 ^t to the memory and a buffer memory for latching the data of the first N (subband division number) samples of the addition result, and when the mute signal is detected, the selector causes the addition means to be added Enter "0"
In a muting device of a sub-band division coding audio decoder which performs muting by switching to the, the sync error detection signal from the sync detector and the CR
A muting device for a subband division coding audio decoder, wherein a CRC error detection signal from the C detector is used as a mute signal. ^{_{Y i t = Y i + N}} t-1 + X i t (i = 0 ··· 2MN-1-N) Y i t = X i t (i = 2MN-N ··· 2MN-1)