JP2001147699A - Audio signal decoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an audio signal decoder which prevents a sound break to prevent a sense of incongruity in listening when reproducing a digital audio signal. SOLUTION: The audio signal decoder 12a takes out and expands a sound group signal, which consists of plural data compressed for every frequency band, every prescribed time is provided with a data detection means 47 which detects whether each compressed data has a value indicating silence or not, an inverse quantization means 44 which expands compressed data to obtain spectrum signals by frequency bands after substituting compressed data with prescribed values on the basis of the detection result of the data detection means 47, and a conversion means 43 which converts the spectrum signals into digital audio signals for every time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an audio signal decoder for expanding a digital audio signal compressed and recorded on a recording medium such as a mini disk.

[0002]

2. Description of the Related Art A mini disc (hereinafter, referred to as "MD") apparatus will be described as an example of a conventional apparatus for compressing a digital audio signal, recording it on a recording medium, and expanding and reproducing it. The MD has a diameter that is about half that of a CD, and a digital audio signal recorded on the MD is converted to an ATRAC (Adaptive T
Data is compressed to about 1/5 by an audio efficient coding method called Ransform Acoustic Coding.

This compression method is performed by an audio signal compressor 30 as shown in FIG. The audio signal is sampled at a predetermined sampling frequency and digitally converted, and then stored in the memory 13. A digital audio signal is sent from the memory 13 to the band division filter 32 every predetermined time, and the L band (DC to 5.5 kHz)
z), M frequency band (5.5 kHz to 11 kHz), and H frequency band (11 kHz to 22 kHz).

The sampling frequency is, for example, 44.1 kHz.
When z is set and a signal every 11.6 msec is defined as one block, 512 digital data are obtained per block. Each digital data is converted by 16 bits,
At this time, the data amount of one block is 1024 bytes.

Next, an MDCT circuit 33 applies a modified discrete cosine transform (MDCT:
Modified Discrte Cosine Transform) operation is performed. Thus, the digital audio signal of each frequency band is converted from a digital signal for each time into a spectrum signal for each frequency. At this time, in the above example, 512 spectrum signals are obtained.

The quantization means 34 allocates more bits to a frequency band that is more important for human auditory characteristics and less bits to a less important frequency band.
The amplitude of each band of the spectrum signal is requantized. The spectrum signal is data-compressed in this way, the obtained compressed data is synthesized by the synthesizing means 35 and output to a memory controller (not shown).

In the MD apparatus, 212 bytes of data compressed from 1024 bytes of data per block are stored in one block.
It is a unit. This one unit signal is called a sound group signal. Each sound group signal is shown in FIG.
, The block sizes BS and BS2, the sub-information amount SIA, SIA2, 52 word lengths WL (i), 52 scale factors SF (i), and audio spectrum data AS
D (i, X (i)).

Here, i is an integer from 0 to 51. X (i) indicates the number of data in each frequency band obtained by dividing 512 spectral signals into 52, and
The sum of X (i) becomes 512.

The block sizes BS and BS2 indicate the mode in which one block is divided, and the same value is input to the first byte and the 212th byte of the sound group signal, respectively. The number of bits of each of the block sizes BS and BS2 is set to 8 bits.

[0010] Sub information amount SI
A and SIA2 indicate the number of data (the number of units) of the word length WL (i) and the scale factor SF (i), and the same value is input to the second byte and the 211th byte of the sound group signal, respectively. Here, SIA =
SIA2 = 52. The number of bits of the sub information amount SIA, SIA2 is set to 8 bits each.

The word length WL (i) is divided into 52 parts of the spectrum signal (sub information amount S).
This is data indicating the number of bits allocated for each frequency band designated by IA), and the number of bits is set to 4 bits. The scale factor SF (i) is data indicating the exponent part of the amplitude of the spectrum signal for each frequency band, and the number of bits is set to 6 bits.

Audio spectrum data ASD
(I, X (i)) is data indicating the mantissa of the amplitude of the spectrum signal by the number of bits allocated to each frequency band, and the word length WL (i) is assigned to each frequency band using human auditory characteristics. ), The number of bytes (the number of bits) is variable.

The total number of bytes of the sound group signal is 212 bytes. By the calculation based on these data, the amplitude of the spectrum signal for each of 512 frequency bands can be calculated.

During reproduction of the MD, the compressed sound group signal is decoded by an audio signal decoder 31 as shown in FIG. The sound group signal is extracted for each block by the decoding means 45 and divided into a word length WL (i), a scale factor SF (i), and audio spectrum data ASD (i, X (i)).

The dequantizing means 44 calculates the dequantized data from each of the divided data.
, The amplitudes of the 512 spectrum signals for each frequency band are calculated. Then, the spectrum signal is divided into three frequency bands of L band, M band, and H band and sent to the IMDCT circuit 43. IMDCT circuit 43
Is the inverse modified discrete cosine transform (IMDCT: Inverse Mo
By performing a "dified Discrte Cosine Transform" operation, the L-band, M-band, and H-band spectrum signals are converted into time-dependent digital signals.

Next, the digital data for each of the L, M, and H bands thus obtained is synthesized by the band synthesis filter 42 to obtain a digital audio signal. Then, a predetermined time length (for example, 11.6 mse
A digital audio signal is sequentially transmitted every c), and is converted into an analog signal at a sampling frequency to obtain an audio signal. Thereby, reproduction is performed.

[0017]

However, according to the above-described compression method, the number of bits allocated according to the frequency band (52) when quantized by the quantization means 34 is different. Therefore, a small signal included in the spectrum signal may be deleted as an inaudible signal by the psychoacoustic model.

At this time, if the sound group signal is decoded by using the above-mentioned conventional audio signal decoder 31, the sound becomes silent at the frequency at which the minute signal was originally contained, and the sound for a moment (for example, 11.6 msec) is reproduced. Cutting occurs. For this reason, although it is said that it cannot be heard by the psychoacoustic model, there is a problem that the viewer actually feels unnatural at the time of viewing.

An object of the present invention is to provide an audio signal decoder capable of preventing interruption of sound when a digital audio signal is reproduced and preventing a sense of discomfort during viewing.

[0020]

SUMMARY OF THE INVENTION In order to achieve the above object, according to the present invention, when compressed data compressed for each frequency band is a value indicating silence, the value is replaced with a predetermined value, and then expanded to obtain a digital signal. It is characterized by obtaining an audio signal.

According to the present invention, there is provided an audio signal decoder for extracting and decompressing a sound group signal composed of a plurality of compressed data compressed for each frequency band at predetermined time intervals, wherein each compressed data has a value indicating silence. Data detecting means for detecting whether or not the compressed data is replaced with a predetermined value based on the detection result of the data detecting means, and then decompressing means for decompressing to obtain a spectrum signal for each frequency band, and the spectrum signal And a converting means for converting a time-dependent digital audio signal into a time-dependent digital audio signal.

According to this configuration, the sound group signal composed of the compressed data for each frequency band is taken into the audio signal decoder every predetermined time, and the data detection means determines whether the compressed data has a value indicating silence for each frequency band. It is determined whether or not. When the compressed data has a value indicating silence, the compressed data is replaced with a predetermined value by the inverse quantization means, and then expanded to obtain a spectrum signal. At this time, a spectrum signal obtained by expanding the predetermined value is assigned to a frequency band having compressed data having a value indicating silence. afterwards,
The converting means converts the spectrum signal, which is a signal for each frequency, into a digital audio signal, which is a signal for each time.

Further, the present invention is characterized in that, in the audio signal decoder having the above-mentioned configuration, the data detecting means detects the presence or absence of compressed data corresponding to the amplitude of the spectrum signal in each frequency band.

The present invention also provides the audio signal decoder having the above-mentioned configuration, further comprising a storage unit for storing the compressed data.
When the compressed data of the preceding sound group signal has a value indicating silence, the replacement of the compressed data of the corresponding frequency band of the subsequent sound group signal is stopped.

According to this configuration, predetermined compressed data of the sound group signal taken into the audio signal decoder is stored in the storage means. When the compressed data of the previous sound group signal stored in the storage means has a value indicating silence, even if the compressed data of the corresponding frequency band of the subsequent sound group signal is a value indicating silence, the compressed data is replaced with the predetermined value. And decode it to a silent state.

According to the present invention, in the audio signal decoder having the above structure, a storage means for storing the compressed data is provided.
When the compressed data of the preceding sound group signal has a value indicating a sound volume higher than a predetermined sound volume, the replacement of the compressed data of the corresponding frequency band of the subsequent sound group signal is stopped.

According to this configuration, predetermined compressed data of the sound group signal taken into the audio signal decoder is stored in the storage means. When the compressed data of the previous sound group signal stored in the storage means has a value indicating a volume greater than a predetermined volume, even if the compressed data of the corresponding frequency band of the subsequent sound group signal is a value indicating silence, It is decompressed without being replaced with the predetermined value and decoded into a silent state.

Further, according to the present invention, in the audio signal decoder having the above configuration, when the compressed data is replaced in a predetermined number of continuous frequency bands in one sound group signal, the compressed data is adjacent to the continuous frequency band. It is characterized in that replacement of compressed data in a frequency band is stopped.

According to this configuration, when the replacement is performed when the compressed data has a value indicating silence in a predetermined number of consecutive frequency bands, the compressed data in a frequency band adjacent to the continuous frequency band indicates silence. Even if it is a value, it is decompressed without being replaced with the predetermined value and decoded into a silent state.

[0030]

Embodiments of the present invention will be described below with reference to the drawings. For convenience of explanation, FIGS.
The same reference numerals are given to the same parts as. FIG.
FIG. 1 is a block diagram showing an MD recording / reproducing apparatus equipped with an audio signal decoder according to one embodiment.

An MD which can be detachably attached to the MD recording / reproducing apparatus.
100 is driven to rotate by the spindle motor 1. The optical pickup 2 includes an objective lens 2 facing the MD100.
a. During reproduction, the MD 100 is irradiated with light from the optical pickup 2 and the reflected light is taken in to read the RF signal (modulated compressed data) recorded on the MD 100 at a rate of 4.3 Mbit / s.

On the other hand, at the time of recording, light stronger than that at the time of reproduction is irradiated from the optical pickup 2 to the MD 100. Thus, the temperature of the recording area on the MD 100 is locally increased. At the time of recording, a modulation magnetic field is applied by a recording head 9 described later to a region on the MD 100 where the temperature has risen, and an RF signal is recorded on the MD 100.

The optical pickup 2 is driven by a feed motor 3
It is transported in the radial direction of D100. Objective lens 2a is M
In order to optimally maintain irradiation of light to the D100 and incidence of reflected light from the MD100, the actuator is slightly moved by an actuator (not shown). The spindle motor 1, the feed motor 3 and the actuator are driven by a drive circuit 4 under the control of a servo circuit 6 described later.

RF read by optical pickup 2
The signal is amplified by the RF amplifier 5. Further, the RF amplifier 5 generates servo signals such as a focus error signal and a tracking error signal from the RF signal. The servo circuit 6 controls the drive circuit 4 based on the servo signal so that the focusing and tracking of the objective lens 2a and the rotation speed of the MD 100 are servo-controlled under the control of a system controller 24 described later.

The modulation / demodulation and error correction circuit 7 demodulates the RF signal amplified by the RF amplifier 5 during reproduction. Then, signal processing such as error correction is performed on the compressed data obtained by demodulation. On the other hand, at the time of recording, the compressed data sent from the memory controller 11 to be described later includes a CIR
After adding C (Cross Interleave Reed-solomon Code), the compressed data is converted to EFM (Eight to Fourteen Modulati).
on) modulation.

The recording head 8 applies a magnetic field to the MD 100 during recording. The recording head drive circuit 9 modulates and demodulates the magnetic field applied by the recording head 8
, Based on a modulated signal obtained by modulating the compressed data. As a result, the magnetic field corresponding to the modulation signal becomes M
D100.

A shock-proof memory 10 composed of a semiconductor memory stores compressed data (during reproduction) output from the modulation / demodulation and error correction circuit 7 or compressed data (during recording) output from a compression / decompression circuit 12 described later. , Are respectively provided for temporarily holding.

Thus, the transfer speed (1.4 Mbits / sec) of the compressed data input / output by the modulation / demodulation and error correction circuit 7 and the transfer speed of the compressed data input / output by the compression / decompression circuit 12 described later (0.3 Mbits / sec) to prevent skipping due to reproduction errors and recording errors caused by disturbances such as vibration.
The shock-proof memory 10 is, for example, 4M
A bit DRAM is appropriate.

The reading and writing 11 of compressed data in the shock proof memory 10 is controlled by the memory controller 11 under the control of the system controller 24. That is, at the time of reproduction, the memory controller 11 stores the compressed data sent from the modulation / demodulation and error correction circuit 7 in the shock proof memory 10. Then, it reads out the compressed data stored in the shock proof memory 10 and outputs it to the compression and decompression circuit 12 described later.

On the other hand, during recording, the compression and decompression circuit 12
The compressed data sent from the storage device is stored in the shockproof memory 10 and the shockproof memory 10
And outputs it to the modulation / demodulation and error correction circuit 7.

The shockproof memory 10 has an area for storing TOC information, which is additional information on audio data, in addition to an area for storing audio data. As soon as MD100 is mounted, M
The TOC information is read from D100 and stored in a predetermined area of the shock proof memory 10 along the same path as the audio data.

Further, in response to a request from the system controller 24, the memory controller 11
Information is read from the shock proof memory 10 and sent to the system controller 24. The system controller 24 determines the MD10 based on the TOC information.
Controls the data read / write operation for 0.

During reproduction, the compression / expansion circuit 12 expands the compressed data output from the memory controller 11 at a rate of 0.3 Mbit / s and outputs a digital audio signal obtained by the expansion. Also, at the time of recording,
The digital audio signal output from the memory 13 is data-compressed by the ATRAC method, and compressed data obtained by the data compression is output to the memory controller 11 at a rate of 0.3 Mbit / s.

During recording, the A / D and D / A converter 14 converts an analog audio signal input via the input / output terminal 18 into a digital digital audio signal and outputs the digital audio signal. At the time of reproduction, the digital audio signal is converted into an analog audio signal and output, and output from the input / output terminal 18 to the outside.

Reference numeral 22 denotes an operation unit for a user to input a command to the MD recording / reproducing apparatus. Reference numeral 23 denotes a display unit for displaying the operation state of the MD recording / reproducing apparatus, the name of the currently reproduced music, and the number of the music under the control of the system controller 24. Reference numeral 24 denotes a system controller which controls the operation of each unit so that the operation of the entire MD recording / reproducing apparatus corresponds to a command input from the operation unit 22, and is constituted by a microcomputer.

The recording operation of the MD recording / reproducing apparatus having the above-described configuration will be described first. An analog audio signal is input to the A / D and D / A converter 14 via the input / output terminal 18. The A / D and D / A converter 14 converts the digital audio signal into a digital audio signal at a sampling frequency of 44.1 kHz and outputs the digital audio signal to the memory 13.

The digital audio signal is sent from the memory 13 to the compression / decompression circuit 12 every predetermined time (for example, 11.6 msec, and in stereo, 5.8 msec because there are Lch and Rch in stereo). Compression and decompression circuit 12
Has the audio signal compressor 30 shown in FIG. A sound group signal (see FIG. 7) is generated by the audio signal compressor 30 and sent to the memory controller 11. The method of generating the sound group signal is the same as described above, and will not be described.

In the modulation / demodulation and error correction circuit 7 at the next stage of the memory controller 11, the sound group signal composed of the compressed data is modulated by the EFM method. The system controller 24 recognizes a recordable area on the MD 100 based on the TOC information, moves the recording head 8 to a recordable area by the magnetic head drive circuit 9, and performs recording on the MD 100.

Next, at the time of reproduction, the optical pickup 2 is driven under the control of the system controller 24, and an RF signal is read from the MD 100. The RF signal is amplified by the RF amplifier 5 and sent to the modulation / demodulation and error correction circuit 7. Further, a servo signal is generated from the RF signal by the RF amplifier 5 and fed back to the servo circuit 6.

The modulation / demodulation and error correction circuit 7 demodulates the RF signal. As a result, compressed data is obtained, subjected to signal processing such as error correction on the compressed data, and then sent to the memory controller 11. The compressed data is sent from the memory controller 11 to the compression and decompression circuit 1 at predetermined time intervals.
2 as a sound group signal (see FIG. 7).

The sound group signal is expanded by an audio signal decoder 12 a described later provided in the compression and expansion circuit 12, and the digital audio signal is stored in the memory 13.
Sent to Then, a predetermined time length (for example, 11.6 m
digital audio signals are sequentially transmitted every second)
An analog signal is obtained at the sampling frequency (44.1 kHz) by an A / D and D / A converter to obtain an audio signal. Thereby, reproduction is performed.

The compression / expansion circuit 12 is provided with an audio signal decoder 12a shown in FIG. The sound group signal input to the audio signal decoder 12a is decoded by the decoding means 45 into a word length WL.
(I), scale factor SF (i), and audio spectrum data ASD (i, X (i)).
As described above, i is an integer from 0 to 51, and X (i)
Indicates the number of data in each frequency band obtained by dividing 512 spectral signals into 52, and the total of X (i) is 512.

Each of the divided data is sequentially sent to the storage means 46, the data detection means 47 and the inverse quantization means 44. The storage means 46 stores predetermined data of the sound group signal, and is used when the inverse quantization means 44 calculates data of the next sound group signal.

The data stored in the storage means 46 are the code bits of the word length, scale factor, and audio spectrum data, and are WLB (i), WLB (i), respectively.
SFB (i) and ASDF (i, X (i)). Further, the data detecting means 47 includes a word length WL (i)
And whether the word length WLB (i) is 0 or not.

The inverse quantization means 44 calculates the amplitudes of 512 spectrum signals for each frequency band from each of the divided data. Then, the spectrum signal is rearranged in the order of the frequency band by the rearranging unit 48, and then divided into three frequency bands of L band, M band, and H band, and sent to the IMDCT circuit 43. IMDCT circuit 43
By performing the inverse modified discrete cosine transform operation,
The L-band, M-band, and H-band spectrum signals are converted into time-dependent digital signals in respective frequency bands.

Next, the L-band and M-band digital signals are synthesized by the ML synthesis filter 50. Furthermore, H
The digital signal of the band and the HML synthesis filter 51 are combined to obtain a digital audio signal of the entire band. Reference numeral 49 denotes delay means for adjusting the timing of the output of the ML synthesis filter 50.

Next, the operation of the audio signal decoder 12a, in particular, the operation of the inverse quantization means 44 will be described with reference to FIG.
This will be described in detail with reference to the flowchart of FIG. First, in step # 101, a one-block sound group signal is input to the decoding means 45. In step # 102, the decoding means 45 converts the sound group signal into 52 word lengths WL (i) and 52 scale factors SF.
(I) 512 audio spectrum data AS
D (i, X (i)).

At step # 103, the counters i and j are initialized, the counter i is incremented, and the steps # 104 to # 11 are sequentially performed for each of the 52 frequency bands.
Step 2 is repeated. In step # 104, the data detecting means 47 detects whether the word length WL (i) is 0 or not. If the word length WL (i) is 0, the flow shifts to step # 105. At this time, the audio spectrum data ASD (i, X (i)) has no data. That is, the amplitude of the spectrum signal is 0, and there is no sound in that frequency band.

If the word length WL (i) is not 0, the audio spectrum data ASD (i, X
(I)) has some data. That is, since the spectrum signal has an amplitude and is not in a silent state in the frequency band, the audio spectrum data ASD
(I, X (i)) is maintained as it is. Then, step # 110, step # 111, step #
In step # 113, the counter i is incremented via 112, and the process returns to step # 104 to proceed to the calculation of the next frequency band.

In step # 105, the data detection means 47 determines whether or not the word length WLB (i) of the previously input sound group signal stored in the storage means 46 is 0.
Is detected. When the word length WLB (i) is 0, since the previous sound group signal was in a silent state, it is determined that the actual audio signal is also in a silent state. Then, the audio spectrum data ASD (i, X (i)) is maintained as it is, and the counter i is incremented in the same manner as described above, and step #
Return to 104.

If the word length WLB (i) is not 0, since the previous sound group signal was not silent, the data of the current sound group signal was determined to have been removed at the time of quantization.
Move to

In step # 106, the data detection means 47 detects whether or not the scale factor SFB (i) of the previously input sound group signal stored in the storage means 46 is larger than a predetermined value. If the scale factor SFB (i) is larger than the predetermined value in the previous sound group signal, if the spectrum signal before quantization is present in the current sound group signal, it is considered to be a signal to some extent.

Therefore, since it is considered that there is a small signal which is removed at the time of quantization, the silent state determined in step # 104 is determined to be correct. Then, the audio spectrum data ASD (i, X (i)) is maintained as it is, the counter i is incremented, and the process returns to step # 104.

If the scale factor SFB (i) is equal to or less than the predetermined value in the previous sound group signal, it is determined that data has been erroneously removed during quantization in the current sound group signal, and the flow shifts to step # 107.

At step # 107, the value of the counter j is determined. The counter j is incremented in step # 109 when the replacement process in step # 108 is performed,
If the replacement process is not performed according to the determinations in steps # 104 to # 106, the process is reset. Therefore, the counter j indicates how many times the replacement process has been performed continuously.

Since the processing shifts in the order of the frequency band according to the increment of the counter i, the continuous replacement processing is performed in the continuous frequency band. For this reason, since it is determined that there is no sound in each of the continuous frequency bands, if the replacement process is performed for a predetermined maximum number of replacements Rmax (i), it is determined that the sound is actually in a silent state. Then, the replacement process is not performed in the next frequency band.
Note that the maximum number of replacements Rmax (i) is determined for each of the 52 frequency bands.

Next, at step # 108, the replacement process shown in FIG. 4 is called. In FIG. 4, step # 121
Then, the counter k is initialized. The counter k is 52
The determination is made in step # 126 and the number is incremented in step # 127 until the number of audio spectrum data in each of the frequency bands reaches the number.

At step # 122, the word length W
L (i) is substituted with the number of bits at the time of replacement, for example, 4;
The minimum value is substituted for the scale factor SF (i).
In step # 123, the data detection unit 47 detects whether the sign bit ASDF (i, k) of the audio spectrum data of the previously input sound group signal stored in the storage unit 46 is a value indicating a positive value. .

If the sign bit ASDF (i, k) is a value indicating a negative value (usually represented by 1), the audio spectrum data ASD (i, k) is added to the audio spectrum data ASD (i, k) by a negative minimum value of 4 bits in step # 125. A certain “1111” is substituted.

If the sign bit ASDF (i, k) is a positive value (usually represented by 0), the audio spectrum data ASD (i, k) has a minimum positive value "0001" in step # 124. Is substituted. Then, in step # 126, the process is repeated until the counter k reaches the number of data indicated by X (i).
At (i), the replacement process in that frequency band ends, and the process returns to the process in FIG.

When the replacement process is completed, step # 109
The counter j is incremented. Then, in step # 111, the word length WL (i) and the scale factor SF (i) of the current sound group signal
Is stored as a word length WLB (i) and a scale factor SFB (i) for the next calculation.
Is stored. Similarly, the sign bit of the spectrum data ASD (i, X (i)) of the current sound group signal is stored in the storage means 46 as the sign bit ASDF (i, X (i)).

In step # 112, it is determined whether or not all the processes of the frequency band divided into 52 have been completed. When the processing is completed (i = 51), the process proceeds to step # 114. In step # 114, a sound group signal including the data replaced by the inverse quantization means 44 (the sound group signal has a data amount larger than 212 bytes).
Is expanded to a spectrum signal.

In the frequency band in which the data has been replaced with "0001" or "1111" in the replacement process (see FIG. 4), a spectrum signal having a small amplitude is generated. Then, as described above, the sorting means 48, IM
A digital audio signal is output through the DCT 49 and the synthesis filters 50 and 51.

In this embodiment, the word length data is set to 0 by the data detecting means 47 (see FIG. 2).
It is determined whether or not the replacement is performed. However, the data is not limited to 0, and the replacement needs to be performed when the data indicates a silent state. For example, if the audio spectrum data indicates a silent state when 1-bit “0”,
The audio spectrum data is reduced to a minimum value (for example, "00
01 ").

The audio signal decoder according to the present embodiment
Although mounted on the D recording / reproducing apparatus, it may be mounted on a reproduction-only MD reproducing apparatus. Further, it can be mounted on a digital audio signal reproducing device using another medium such as a floppy disk or a hard disk.

[0076]

According to the present invention, even if the sound group signal is data indicating a silent state, the sound group signal is replaced with predetermined data at the time of decoding. It is possible to prevent the sound from being cut off without a silent state afterward. This can prevent discomfort during viewing.

Further, according to the present invention, when data indicating a silent state is temporally continuous in the same frequency band of a sound group signal, data before a predetermined time before data indicating a silent state in the same frequency band indicates a large volume. In the case of the value, or when a predetermined number of data indicating the silence state continues in the adjacent frequency band, the replacement of the data is stopped. Decoding into an amplitude signal can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an MD recording / reproducing apparatus equipped with an audio signal decoder according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating an audio signal decoder according to the embodiment of the present invention.

FIG. 3 is a flowchart showing an operation of the audio signal decoder according to the embodiment of the present invention.

FIG. 4 is a flowchart illustrating an operation of a replacement process of the audio signal decoder according to the embodiment of the present invention.

FIG. 5 is a block diagram showing a conventional audio signal compressor.

FIG. 6 is a block diagram showing a conventional audio signal decoder.

FIG. 7 is a diagram showing a sound group signal.

[Explanation of symbols]

 Reference Signs List 1 spindle motor 2 optical pickup 2a objective lens 3 feed motor 4 drive circuit 5 RF amplifier 6 servo circuit 7 modulation / demodulation and error correction circuit 8 recording head 9 recording head drive circuit 10 shock proof memory 11 memory controller 12 compression / decompression circuit 12a, 31 Audio signal decoder 13 memory 14 A / D and D / A converter 18 input / output terminal 22 operation unit 23 display unit 24 system controller 30 audio signal compressor 32 band division filter 33 MDCT 34 quantization unit 35 synthesis unit 42 band synthesis filter 43 IMDCT 44 Inverse quantization means 45 Decoding means

Claims (6)

[Claims] 1. An audio signal decoder, wherein, when compressed data compressed for each frequency band has a value indicating silence, the value is replaced with a predetermined value and then decompressed to obtain a digital audio signal. 2. An audio signal decoder for extracting and decompressing a sound group signal composed of a plurality of compressed data compressed for each frequency band at predetermined time intervals and detecting whether or not each of the compressed data has a value indicating silence. Data decompression means, and a dequantization means for replacing the compressed data with a predetermined value based on the detection result of the data detection means, and then decompressing to obtain a spectrum signal for each frequency band, An audio signal decoder, comprising: conversion means for converting the digital audio signal into a digital audio signal. 3. The audio signal decoder according to claim 2, wherein said data detection means detects the presence or absence of compressed data corresponding to the amplitude of a spectrum signal in each frequency band. 4. A storage means for storing the compressed data, wherein when two consecutive sound group signals have a value indicating silence in the compressed data of the previous sound group signal, the sound data corresponds to the sound group signal of the subsequent sound group signal. 4. The audio signal decoder according to claim 2, wherein replacement of compressed data in a frequency band is stopped. 5. A storage means for storing the compressed data, wherein when two consecutive sound group signals have a value indicating that the compressed data of the preceding sound group signal has a sound volume higher than a predetermined sound volume, the sound data of the subsequent sound group signal is determined. 4. The audio signal decoder according to claim 2, wherein replacement of the compressed data of the corresponding frequency band of the sound group signal is stopped. 6. When replacing the compressed data in a predetermined number of continuous frequency bands in one sound group signal, stopping replacement of the compressed data in a frequency band adjacent to the continuous frequency band. The audio signal decoder according to claim 2 or 3, wherein