JP3250367B2 - Encoded signal decoding method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for decoding a coded signal, for example, by bit-compressing input data obtained by digitizing a continuous signal, recording the data on a disk-shaped recording medium, and performing bit compression from the disk-shaped recording medium. The present invention is applied to a disk recording / reproducing apparatus in which reproduced data is obtained by reproducing the data and expanding the bits.

[0002]

2. Description of the Related Art In recent years, with the advancement and development of high-efficiency coding technology, it is time to expand the field of application of technology for high-efficiency coding of digital signals such as audio and video.
In a high-efficiency coding method of a signal such as audio or voice, for example, band division coding (sub-band coding) in which an audio signal on a time axis is divided into a plurality of frequency bands by a filter and coded. : SBC)
And the like. In addition, a signal on the time axis is converted into a signal on the frequency axis (orthogonal conversion) and divided into a plurality of frequency bands,
Transform coding, etc., which encodes each band.

Further, a high-efficiency coding method combining the above-described band division coding and transform coding has been considered. In this case, for example, division into several bands by the above-mentioned band division coding is performed. After that, the signal for each band is orthogonally transformed into a signal on the frequency axis, and encoding is performed for each of the orthogonally transformed bands.

Here, as a filter for the above-mentioned band division, for example, there is a QMF filter, and a 1976 REC
rochier, Digital coding of speech in subbands, BellS
yst.Tech. J. Vol.55, No.8 1976. Also ICASSP 83, BOSTON Polyphase Quadrature filters-A
New subband coding techniqe, Joseph H. Rothweiler, describes an equal-bandwidth filter partitioning technique. Next, as the above-described orthogonal transform, for example, an input audio signal is divided into blocks in a predetermined time unit (frame), and a time axis is converted to a frequency axis by performing a modified DCT transform (MDCT) or the like for each block. Things. ICASSP 1987 Subband for MDCT
/ Transform Coding Using Filter Bank Designs Based
on TimeDomain Aliasing Cancellation, JPPrincen,
ABBradley, Univ. Of SurreyRoyal Melbourne Inst.
of Tech.

[0005] Further, as a frequency division width for quantizing each frequency component obtained by dividing the frequency band, for example, band division using human psychoacoustic characteristics or the like is performed, and when encoding data for each band, Is subjected to encoding by adaptive bit allocation for each band. For example, when encoding the data obtained by the MDCT processing by the bit allocation, the MDCT data of each block is encoded with an adaptive number of allocated bits.

[0006] The encoding method is used to
FIG. 7 shows an example of encoded data of an audio signal. FIG.
, 22 is scale information (scale factor) generally corresponding to an exponent part in a floating-point notation. Reference numeral 23 denotes the number of bits allocated to each block, and is allocated bit information (word length) corresponding to the number of digits of the mantissa in floating-point notation. 24
Is spectral component data of each block, and is spectral information (spectral data) corresponding to data included in the mantissa when floating-point notation is used. The scale information 22 and the allocated bit number information 23 divide the input spectrum data into a plurality of bands (blocks) (for example, 5
The block is divided into two blocks, and blocks 0, 1, 2,... ), One is assigned to each block.

FIG. 8 is an enlarged view of the scale factor 22, the word length 23 and the spectrum data 24 of FIG. 7, and the scale factors 22 (1) to 22 (3) of the blocks 0 to n and the blocks 0 to The word lengths 23 (1) to 23 (3) of the block n and the spectrum data 24 (1) to 24 (3) of the blocks 0 to n are obtained.

Further, in order to know whether or not an error has occurred in the data, the encoded data shown in FIG. 7 is composed of a data stream as shown in FIG. It is divided into 15 (a), and an error flag 15 (b) indicating whether each byte contains an error.
The configuration is added. When the error flag is 1, an error is included in the byte data 15 (a), and when the error flag is 0, no error is included in the byte data.

FIG. 2 shows the configuration of a conventional coded signal decoding device to which the coded signal as described above is input. In FIG. 2, reference numeral 7 denotes an input terminal of the coded signal decoding device, 8 denotes a demultiplexer unit, 9 denotes an inverse quantization unit, 10 denotes an inverse normalization unit, 11 denotes an IMDCT unit, and 12 denotes a PCM audio data output terminal. .

Next, the operation of the above conventional example will be described. 2, the coded signal from the input terminal 7 is input to the demultiplexer unit 8, where the scale factor (for example, 22 (1) to 22 (3) in FIG. 8 and the number of allocated bits (for example, FIG.
23 (1) to 23 (3)), spectrum data (for example, FIG.
24 (1) to 24 (3)).

The inverse quantization unit 9 performs an inverse quantization process on the data based on the number of allocated bits and the spectrum data, and outputs the data to the inverse normalization unit 10.

The inverse normalizing section 10 performs inverse normalization of the data from the scale factor and the output of the inverse quantizing section 9 and converts the data into spectrum data as shown in FIG. In FIG.
D1 to D8 represent the intensities of the spectrum data for each frequency band, and are output as spectrum data (data on the frequency axis) thus denormalized.

The IMDCT unit 11 orthogonally transforms the denormalized spectrum data by IMDCT processing into data in a time domain, and as shown in FIG.
The signal is output to the output terminal 12 as a PCM digital audio signal including a frequency component of DC to 20 KHz.

As described above, the conventional encoded signal decoding apparatus can decode a digital audio signal from highly efficient encoded data.

[0015]

However, the above-described conventional coded signal decoding apparatus performs the above-described inverse quantization when an error occurs in coded data as shown in FIG. Therefore, the encoded signal cannot be decoded, and the PCM audio data to be decoded is muted or noise occurs.

Referring to FIG. 3, a case where spectrum data is extracted from a data stream will be described. In FIG. 3, 13 (1) to 13 (4) are obtained by dividing an input data stream into byte units. 13
(1a) to 13 (4a) are error flags (1 indicates an error, 0 indicates no error) indicating whether or not each byte contains an error. Further, 14 (1) to 14 (8) are obtained by extracting data with a word length of 2 to 16 bits from the data stream. Byte (n-1) 13 (2) and Byte (n-1) 13 (2) are stored in the data extraction buffer. When data of 2 bytes of (n) is input from the data stream, there are eight patterns of byte straddling when extracting data having a word length of 2 to 16 bits from this buffer. Some data spans 3 bytes for) and 14 (5).

When such data is extracted, it is checked whether or not there is an error for each byte including the extracted data, and if an error is included, processing such as setting the data to 0 is performed. However, there are eight cases, and when extracting one piece of data, it is necessary to check an error flag of up to three bytes, which requires large-scale hardware and is difficult to realize. Was.

The present invention solves such a conventional problem, and minimizes deterioration of sound quality even when a data error occurs in a highly efficient coded signal with hardware of the same scale as a conventional device. It is an object of the present invention to provide an excellent coded signal decoding device capable of performing an inverse quantization process on data and decoding an audio signal while limiting the number of data.

[0019]

According to the present invention, in order to achieve the above object, in an inverse quantization process performed by an inverse quantization unit, only an error flag of a byte including the most significant bit of data to be extracted is determined. After the confirmation, the data to be extracted is set to 0 only when the most significant byte contains an error.

[0020]

Therefore, according to the present invention, by checking the presence or absence of an error in a byte containing the most significant bit of data to be dequantized, it is possible to set the data to be dequantized to 0 when an error occurs. it can.

Even when an error occurs in a byte other than the most significant byte of the data to be extracted, the most significant data is not an error. For example, when the extracted data is 8 bits and the upper byte includes 7 bits, The data resolution is 8
This is equivalent to only dropping from 7 bits to 7 bits, and has the effect of being able to interpolate into data close to the information of the original data.

Further, since the checking of the presence / absence of an error is performed only for the byte including the most significant bit of the data to be extracted, the number of times of checking the error flag and the classification of the error pattern are reduced, and the processing of the inverse quantization unit is reduced. Can be realized by simple hardware, and there is an effect that deterioration of sound quality can be minimized without greatly increasing a processing load for performing interpolation processing when data has an error.

[0023]

FIG. 1 shows an embodiment of the present invention, and is a flowchart showing the inverse quantization process performed by the inverse quantization unit 9 in FIG. In other words, the configuration of the coded signal decoding apparatus in the embodiment of the present invention is the same as the conventional configuration shown in FIG. 2, but in particular, the method of processing in the inverse quantization unit 9 is characterized. Things. Before describing the inverse quantization processing of FIG. 1, data input to the inverse quantization unit 9 will be described first.

FIG. 5 shows the presence / absence of an error in each byte of the spectrum data and the spectrum data stream input to the inverse quantization unit 9 in FIG. 2, and shows how the number of allocated bits is extracted. In FIG. 5, 16 (1) to 16 (4)
Is a byte obtained by dividing the spectrum data stream (in this case, a unit used for error detection is a byte)
Here, 16 (1a) to 16 (4a) are error flags indicating whether or not the byte contains an error. Here, when the error flag is 1, the corresponding byte includes an error, and when the error flag is 0, it indicates that there is no error in the corresponding byte. Therefore, byte A (16 (1)) and byte B (16 (1))
(2)), byte D (16 (4)) is an error-free byte, and byte C is an error-containing byte.

DATA (n-1) (17 (1)), DATA (n) (17 (2)),
DATA (n + 1) (17 (3)) is data obtained by extracting the number of allocated bits from the spectrum data stream, and 18 is DATA (n) (1
7 (2)) is the original value when there is no error in the byte C (16 (3)). Next, the manner in which DATA (n) (17 (2)) having no error in the most significant bit (MSB) of data is dequantized will be described with reference to the flowchart of FIG. Byte B (16 including the MSB of DATA (n)
Since there is no error in (2)) (step 1), it is checked whether there is data for the number of extracted bits (8 bits in this example) in the bit extraction buffer (step 2a).

However, since 8-bit data cannot be extracted from byte B, the next byte C (16 (3)) is input from the spectrum data stream (step 3).
a). Further, it is confirmed whether data for the number of extracted bits has been input to the bit extraction buffer (step 4).
a).

Since 13-bit data is stored in the buffer, 5-bit data is extracted from byte B and 3-bit data is extracted from byte C, and DATA (n) is inversely quantized (step 5).

In this case, since there is no error in the byte B containing the MSB of DATA (n), even if there is an error in the byte C which is the lower bit part of DATA (n), it is inversely quantized.

Further, how the data DATA (n + 1) containing an error in the MSB of the data is inversely quantized will be described with reference to the flowchart of FIG. It is checked whether an error is contained in the byte C containing the MSB of DATA (n + 1) (step 1). It is confirmed whether data of the number of extracted bits (8 bits in this case) is present in the bit extraction buffer (step 2b). Here, since only three bits remain in the buffer, the next byte D is read from the spectrum data stream into the buffer.

Since the bit extraction buffer has 13-bit data, the process proceeds to the next process.
Since the MSB contains an error, the data corresponding to the number of extracted bits is dequantized as 0 (step 6).

The inverse quantization process is performed as described above. FIG. 6 shows the data DATA (n) (17) extracted in FIG.
(2)) represents the difference in the inversely quantized value due to the difference in the processing method when inversely quantized.

DATA (n) cannot decode its true value because there is an error in the portion included in byte C on the least significant bit (LSB) side. Reference numeral 19 denotes a case where there is no error in DATA (n), that is, a true inverse quantization value.
Only the byte B containing the MSB of TA (n) is error-checked and represents a value dequantized by the method shown in the flow chart of FIG. 1, and 21 indicates an error in the byte C containing the LSB of DATA (n). Therefore, the value represents a case where DATA (n) is regarded as an error and all the extracted bits are interpolated with 0.

As can be seen from this example, the dequantized values are 65 for the original 19, 71 for the error check of block B only, 21 for 0, and 21 for 0 when the interpolation is performed.
By making use of the byte containing the MSB of the data to be extracted, it is possible to make the value close to the true value even if there is an error in the data on the LSB side. In this example, 8-bit data is only required to be reduced to 5-bit precision. This means that the more bits included in the byte on the MSB side, the closer to the true value can be interpolated.

[0034]

According to the present invention, as is apparent from the above description,
It has the following effects. (1) Only the error of the byte containing the most significant bit of the spectrum data is checked. If there is no error in the byte, the data containing the most significant bit is utilized and the data is inversely quantized. Compared with the method of clearing the spectrum to be converted as an error, the difference from the original data is small, and in particular, there is an effect that the more the number of bytes of the byte including the upper bit is, the closer to the original value. (2) When performing inverse quantization of data, the presence or absence of an error in the data extracted from the spectrum data is checked by examining only the byte including the most significant bit of the extraction block. Even if it extends over bytes, inverse quantization can be performed only by checking the error flag once, which simplifies the processing of the inverse quantization unit, reduces the size of the hardware, and has the same hardware scale as before. This has the effect that the encoded signal decoding device can be realized at a high processing speed.

[Brief description of the drawings]

FIG. 1 is a flowchart of an inverse quantization process performed by an inverse quantization unit of an encoded signal decoding device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of an encoded signal decoding apparatus according to an embodiment of the present invention and a conventional example.

FIG. 3 is an error pattern diagram of data generated at the time of inverse quantization.

FIG. 4 is an explanatory diagram in which a data stream input to the apparatus is divided into bytes and an error detection flag for each byte is added;

FIG. 5 is an explanatory diagram of data to be inversely quantized when an error occurs in a part of the spectrum data stream in the embodiment of the present invention.

FIG. 6 is a diagram showing a difference in value due to a difference in processing of dequantized data DATA (n) in FIG.

FIG. 7 is an explanatory diagram of a coded signal input to the apparatus.

FIG. 8 is an enlarged view of the encoded signal of FIG. 7;

FIG. 9 is a spectrum diagram showing the intensity of spectrum data after denormalization of the encoded signal decoding device.

FIG. 10 is a waveform chart showing PCM audio data output from the IMDCT unit of the encoded signal decoding device.

[Explanation of symbols]

 7 input terminal 8 demultiplexer unit 9 inverse quantization unit 10 inverse normalization unit 11 IMDCT unit 12 output terminal

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI G11B 20/18 560 H03M 7/30 A 570 G10L 7/04 G H03M 7/30 9/18 J (58) Fields surveyed (Int. .Cl. ⁷ , DB name) H03M 13/00 G10L 19/00 G11B 20/00 H03M 7/00

Claims (2)

(57) [Claims] 1. A data stream that is divided into block units and includes an error flag indicating the presence / absence of an error of the block in the block unit is different from a break of the block unit including the error flag from the data stream. When extracting data in units, only the error flag of the block containing the most significant bit of the data to be extracted is detected, and if the error flag indicates that there is no error, the encoded signal decoding that validates the extracted data Method. 2. A system for decoding bit-compressed data, comprising: forming a bit stream by concatenating a plurality of data encoded in an error detection variable length format; A decoding device for combining a signal recorded, reproduced or transmitted by adding a correction code, and a means for detecting an error in data to be decoded using the correction code and an interpolation means for interpolating erroneous data. When the data to be decoded spans a plurality of error detection blocks, only the error detection block including the most significant bit of the data is checked, and only when the error detection block has an error. An encoded signal decoding device configured to interpolate and decode the decoded data.