Method and apparatus for sub-band coding and decoding

• US 6,625,574 B1
• Filed: 08/25/2000
• Issued: 09/23/2003
• Est. Priority Date: 09/17/1999
• Status: Expired due to Fees

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Taniguchi, Shohei, Banba, Yutaka
• Primary Examiner(s): Chawan, Vijay
• Application Number:
  US09/645,326
• Time in Patent Office: 1,124 Days
• Field of Search: 704/229, 704/214, 704/230, 704/219, 704/200.1, 704/212, 704/500-504, 704/205, 704/258, 704/203, 704/225, 375/240.12, 375/253, 375/240.03, 375/240.11, 375/240.24, 375/240-243, 381/2, 381/22
• US Class Current: 704/229
• CPC Class Codes: G10L 19/0208 Subband vocoders

Abstract

An input digital audio signal is divided into sub-band signals in respective sub-bands. Scale factors of the respective sub-bands are determined on the basis of the sub-band signals for every frame. Calculation is made as to differences between the determined scale factors for a first frame and the determined scale factors for a second frame preceding the first frame. Absolute values of the calculated scale-factor differences are calculated, and data representative of the calculated absolute values are generated. The data representative of the calculated absolute values are encoded into data of a Huffman code. Sign bits are generated which represent signs of the calculated scale-factor differences. The sub-band signals are quantized in response to the determined scale factors for every frame to generate quantized samples of the sub-band signals. The Huffman-code data, the generated sign bits, and the quantized samples of the sub-band signals are combined into a bit stream.

Claims

1. A method of sub-band coding, comprising the steps of:

dividing an input digital audio signal into sub-band signals in respective sub-bands;

determining scale factors of the respective sub-bands on the basis of the sub-band signals for every frame;

calculating differences between the determined scale factors for a first frame and the determined scale factors for a second frame preceding the first frame;

calculating absolute values of the calculated scale-factor differences and generating data representative of the calculated absolute values;

encoding the data representative of the calculated absolute values into data of a Huffman code;

generating sign bits representing signs of the calculated scale-factor differences;

quantizing the sub-band signals in response to the determined scale factors for every frame to generate quantized samples of the sub-band signals; and

combining the Huffman-code data, the generated sign bits, and the quantized samples of the sub-band signals into a bit stream.

4. A method as recited in claim 1, wherein the sign-bit generating step comprises preventing generation of a sign bit corresponding a calculated scale-factor difference which is equal to zero.

5. A method as recited in claim 1, wherein the Huffman code is a run-length type.

6. A method as recited in claim 1, further comprising the step of fixing the determined scale factors to maximum values and preventing the determined scale factors from being updated during a predetermined time interval.

7. A method of sub-band decoding for a bit stream generated by the method in claim 1, comprising the steps of:

extracting Huffman-code data from the bit stream;

decoding the extracted Huffman-code data into data representative of absolute values of scale-factor differences;

extracting sign bits from the bit stream;

calculating scale factors of respective sub-bands on the basis of the extracted sign bits and the data representative of the absolute values of the scale-factor differences;

deriving first sub-band signals in the respective sub-bands from the bit stream in response to the calculated scale factors;

inversely quantizing the first sub-band signals into second sub-band signals in response to the calculated scale factors; and

combining the second sub-band signals into an original digital audio signal.

8. A method as recited in claim 7, wherein the Huffman-code data comprise run-length Huffman code data.

2. A method of sub-band coding, comprising the steps of:

dividing an input digital audio signal into sub-band signals in respective sub-bands;

separating the sub-bands into groups on the basis of a perceptual model;

determining scale factors of the respective sub-band groups on the basis of the sub-band signals for every frame;

calculating differences between the determined scale factors for a first frame and the determined scale factors for a second frame preceding the first frame;

calculating absolute values of the calculated scale-factor differences and generating data representative of the calculated absolute values;

encoding the data representative of the calculated absolute values into data of a Huffman code;

generating sign bits representing signs of the calculated scale-factor differences;

quantizing the sub-band signals in response to the determined scale factors for every frame to generate quantized samples of the sub-band signals; and

combining the Huffman-code data, the generated sign bits, and the quantized samples of the sub-band signals into a bit stream.

3. A method of sub-band decoding for a bit stream generated by the method in claim 2, comprising the steps of:

extracting Huffman-code data from the bit stream;

decoding the extracted Huffman-code data into data representative of absolute values of scale-factor differences;

extracting sign bits from the bit stream;

calculating scale factors of respective sub-band groups on the basis of the extracted sign bits and the data representative of the absolute values of the scale-factor differences;

deriving first sub-band signals in the respective sub-bands from the bit stream in response to the calculated scale factors;

inversely quantizing the first sub-band signals into second sub-band signals in response to the calculated scale factors; and

combining the second sub-band signals into an original digital audio signal.

9. A method of sub-band coding, comprising the steps of:

dividing an input digital audio signal into sub-band signals in respective sub-bands;

determining scale factors of the respective sub-bands on the basis of the sub-band signals for every frame;

calculating differences between the determined scale factors for a first frame and the determined scale factors for a second frame preceding the first frame;

calculating absolute values of the calculated scale-factor differences and generating data representative of the calculated absolute values;

encoding the data representative of the calculated absolute values into data of a Huffman code;

generating sign bits representing signs of the calculated scale-factor differences;

generating selection information representing a selected bit-stream format;

quantizing the sub-band signals in response to the determined scale factors for every frame to generate quantized samples of the sub-band signals;

combining the generated selection information, the Huffman-code data, the generated sign bits, and the quantized samples of the sub-band signals into a bit stream of a first format;

generating information flags indicating whether or not the determined scale factors for the first frame are updated from the determined scale factors for the second frame, respectively;

selecting one or more of the scale factors in the first frame which are updated from those in the second frame, and generating selected-scale-factor data representative of the selected scale factor or the selected scale factors;

combining the generated selection information, the generated information flags, the selected-scale-factor data, and the quantized samples of the sub-band signals into a bit stream of a second format; and

selecting one of the bit stream of the first format and the bit stream of the second format as an output bit stream to maximize a number of bits allocated to the samples of the sub-band signals.

10. A method of sub-band decoding for a bit stream generated by the method in claim 9, comprising the steps of:

detecting selection information in the bit stream;

deciding whether the bit stream is of a first format or a second format on the basis of the detected selected information;

extracting Huffman-code data from the bit stream when it is decided that the bit stream of the first format;

decoding the extracted Huffman-code data into data representative of absolute values of scale-factor differences;

extracting sign bits from the bit stream when it is decided that the bit stream of the first format;

calculating first scale factors of respective sub-bands on the basis of the extracted sign bits and the data representative of the absolute values of the scale-factor differences;

extracting information flags from the bit stream when it is decided that the bit stream is of the second format;

extracting selected-scale-factor data from the bit stream when it is decided that the bit stream is of the second format;

calculating second scale factors of respective sub-bands on the basis of the extracted information flags and the extracted selected-scale-factor data;

deriving first sub-band signals in the respective sub-bands from the bit stream in response to the first scale factors or the second scale factors;

inversely quantizing the first sub-band signals into second sub-band signals in response to the first scale factors or the second scale factors; and

combining the second sub-band signals into an original digital audio signal.

11. A method of sub-band coding, comprising the steps of:

dividing an input digital audio signal into sub-band signals in respective sub-bands;

separating the sub-bands into groups on the basis of a perceptual model;

determining scale factors of the respective sub-band groups on the basis of the sub-band signals for every frame;

calculating differences between the determined scale factors for a first frame and the determined scale factors for a second frame preceding the first frame;

calculating absolute values of the calculated scale-factor differences and generating data representative of the calculated absolute values;

encoding the data representative of the calculated absolute values into data of a Huffman code;

generating sign bits representing signs of the calculated scale-factor differences;

generating selection information representing a selected bit-stream format;

quantizing the sub-band signals in response to the determined scale factors for every frame to generate quantized samples of the sub-band signals;

combining the generated selection information, the Huffman-code data, the generated sign bits, and the quantized samples of the sub-band signals into a bit stream of a first format;

generating information flags indicating whether or not the determined scale factors for the first frame are updated from the determined scale factors for the second frame, respectively;

selecting one or more of the scale factors in the first frame which are updated from those in the second frame, and generating selected-scale-factor data representative of the selected scale factor or the selected scale factors;

combining the generated selection information, the generated information flags, the selected-scale-factor data, and the quantized samples of the sub-band signals into a bit stream of a second format; and

selecting one of the bit stream of the first format and the bit stream of the second format as an output bit stream to maximize a number of bits allocated to the samples of the sub-band signals.

12. A method of sub-band decoding for a bit stream generated by the method in claim 11, comprising the steps of:

detecting selection information in the bit stream;

deciding whether the bit stream is of a first format or a second format on the basis of the detected selected information;

extracting Huffman-code data from the bit stream when it is decided that the bit stream of the first format;

decoding the extracted Huffman-code data into data representative of absolute values of scale-factor differences;

extracting sign bits from the bit stream when it is decided that the bit stream of the first format;

calculating first scale factors of respective sub-band groups on the basis of the extracted sign bits and the data representative of the absolute values of the scale-factor differences;

extracting information flags from the bit stream when it is decided that the bit stream is of the second format;

extracting selected-scale-factor data from the bit stream when it is decided that the bit stream is of the second format;

calculating second scale factors of the respective sub-band groups on the basis of the extracted information flags and the extracted selected-scale-factor data;

deriving first sub-band signals in the respective sub-bands from the bit stream in response to the first scale factors or the second scale factors;

inversely quantizing the first sub-band signals into second sub-band signals in response to the first scale factors or the second scale factors; and

combining the second sub-band signals into an original digital audio signal.

13. A sub-band coding apparatus comprising:

means for dividing an input digital audio signal into sub-band signals in respective sub-bands;

means for determining scale factors of the respective sub-bands on the basis of the sub-band signals for every frame;

means for calculating differences between the determined scale factors for a first frame and the determined scale factors for a second frame preceding the first frame;

means for calculating absolute values of the calculated scale-factor differences and generating data representative of the calculated absolute values;

means for encoding the data representative of the calculated absolute values into data of a variable-length code;

means for generating sign bits representing signs of the calculated scale-factor differences;

means for quantizing the sub-band signals in response to the determined scale factors for every frame to generate quantized samples of the sub-band signals; and

means for combining the variable-length-code data, the generated sign bits, and the quantized samples of the sub-band signals into a bit stream.

14. A sub-band coding apparatus comprising:

means for dividing an input digital audio signal into sub-band signals in respective sub-bands;

means for separating the sub-bands into groups on the basis of a perceptual model;

means for determining scale factors of the respective sub-band groups on the basis of the sub-band signals for every frame;

means for calculating differences between the determined scale factors for a first frame and the determined scale factors for a second frame preceding the first frame;

means for calculating absolute values of the calculated scale-factor differences and generating data representative of the calculated absolute values;

means for encoding the data representative of the calculated absolute values into data of a variable-length code;

means for generating sign bits representing signs of the calculated scale-factor differences;

means for quantizing the sub-band signals in response to the determined scale factors for every frame to generate quantized samples of the sub-band signals; and

means for combining the variable-length-code data, the generated sign bits, and the quantized samples of the sub-band signals into a bit stream.

15. A sub-band coding apparatus comprising:

means for dividing an input digital audio signal into sub-band signals in respective sub-bands;

means for determining scale factors of the respective sub-bands on the basis of the sub-band signals for every frame;

means for calculating differences between the determined scale factors for a first frame and the determined scale factors for a second frame preceding the first frame;

means for calculating absolute values of the calculated scale-factor differences and generating data representative of the calculated absolute values;

means for encoding the data representative of the calculated absolute values into data of a variable-length code;

means for generating sign bits representing signs of the calculated scale-factor differences;

means for generating information flags indicating whether or not the determined scale factors for the first frame are updated from the determined scale factors for the second frame, respectively;

means for selecting one or more of the scale factors in the first frame which are updated from those in the second frame, and generating selected-scale-factor data representative of the selected scale factor or the selected scale factors;

means for calculating a first sum of a total number of bits of the variable-length-code data and a total number of bits of the sign bits;

means for calculating a second sum of a total number of bits of the information flags and a total number of bits of the selected-scale-factor data;

means for deciding whether or not the first sum is smaller than the second sum;

means for generating selection information in accordance with a result of the deciding whether or not the first sum is smaller than the second sum;

means for quantizing the sub-band signals in response to the determined scale factors for every frame to generate quantized samples of the sub-band signals;

means for combining the generated selection information, the variable-length-code data, the generated sign bits, and the quantized samples of the sub-band signals into a bit stream when it is decided that the first sum is smaller than the second sum; and

means for combining the generated selection information, the generated information flags, the selected-scale-factor data, and the quantized samples of the sub-band signals into a bit stream when it is decided that the first sum is not smaller than the second sum.

16. A sub-band coding apparatus comprising:

means for dividing an input digital audio signal into sub-band signals in respective sub-bands;

means for separating the sub-bands into groups on the basis of a perceptual model;

means for determining scale factors of the respective sub-band groups on the basis of the sub-band signals for every frame;

means for calculating differences between the determined scale factors for a first frame and the determined scale factors for a second frame preceding the first frame;

means for calculating absolute values of the calculated scale-factor differences and generating data representative of the calculated absolute values;

means for encoding the data representative of the calculated absolute values into data of a variable-length code;

means for generating sign bits representing signs of the calculated scale-factor differences;

means for generating information flags indicating whether or not the determined scale factors for the first frame are updated from the determined scale factors for the second frame, respectively;

means for selecting one or more of the scale factors in the first frame which are updated from those in the second frame, and generating selected-scale-factor data representative of the selected scale factor or the selected scale factors;

means for calculating a first sum of a total number of bits of the variable-length-code data and a total number of bits of the sign bits;

means for calculating a second sum of a total number of bits of the information flags and a total number of bits of the selected-scale-factor data;

means for deciding whether or not the first sum is smaller than the second sum;

means for generating selection information in accordance with a result of the deciding whether or not the first sum is smaller than the second sum;

means for quantizing the sub-band signals in response to the determined scale factors for every frame to generate quantized samples of the sub-band signals;

means for combining the generated selection information, the variable-length-code data, the generated sign bits, and the quantized samples of the sub-band signals into a bit stream when it is decided that the first sum is smaller than the second sum; and

means for combining the generated selection information, the generated information flags, the selected-scale-factor data, and the quantized samples of the sub-band signals into a bit stream when it is decided that the first sum is not smaller than the second sum.

17. A sub-band decoding apparatus comprising:

means for extracting variable-length-code data from a bit stream;

means for decoding the extracted variable-length-code data into data representative of absolute values of scale-factor differences;

means for extracting sign bits from the bit stream;

means for calculating scale factors of respective sub-bands on the basis of the extracted sign bits and the data representative of the absolute values of the scale-factor differences,

means for deriving first sub-band signals in the respective sub-bands from the bit stream in response to the calculated scale factors;

means for inversely quantizing the first sub-band signals into second sub-band signals in response to the calculated scale factors; and

means for combining the second sub-band signals into an original digital audio signal.

18. A sub-band decoding apparatus comprising:

means for extracting variable-length-code data from a bit stream;

means for decoding the extracted variable-length-code data into data representative of absolute values of scale-factor differences;

means for extracting sign bits from the bit stream;

means for calculating scale factors of respective sub-band groups on the basis of the extracted sign bits and the data representative of the absolute values of the scale-factor differences;

means for deriving first sub-band signals in the respective sub-bands from the bit stream in response to the calculated scale factors;

means for inversely quantizing the first sub-band signals into second sub-band signals in response to the calculated scale factors; and

means for combining the second sub-band signals into an original digital audio signal.

19. A sub-band decoding apparatus comprising:

means for detecting selection information in a bit stream;

means for deciding whether the bit stream is of a first format or a second format on the basis of the detected selected information;

means for extracting variable-length-code data from the bit stream when it is decided that the bit stream of the first format;

means for decoding the extracted variable-length-code data into data representative of absolute values of scale-factor differences;

means for extracting sign bits from the bit stream when it is decided that the bit stream of the first format;

means for calculating first scale factors of respective sub-bands on the basis of the extracted sign bits and the data representative of the absolute values of the scale-factor differences;

means for extracting information flags from the bit stream when it is decided that the bit stream is of the second format;

means for extracting selected-scale-factor data from the bit stream when it is decided that the bit stream is of the second format;

means for calculating second scale factors of respective sub-bands on the basis of the extracted information flags and the extracted selected-scale-factor data;

means for deriving first sub-band signals in the respective sub-bands from the bit stream in response to the first scale factors or the second scale factors;

means for inversely quantizing the first sub-band signals into second sub-band signals in response to the first scale factors or the second scale factors; and

means for combining the second sub-band signals into an original digital audio signal.

20. A sub-band decoding apparatus comprising:

means for detecting selection information in a bit stream;

means for deciding whether the bit stream is of a first format or a second format on the basis of the detected selected information;

means for extracting variable-length-code data from the bit stream when it is decided that the bit stream of the first format;

means for decoding the extracted variable-length-code data into data representative of absolute values of scale-factor differences;

means for extracting sign bits from the bit stream when it is decided that the bit stream of the first format;

means for calculating first scale factors of respective sub-band groups on the basis of the extracted sign bits and the data representative of the absolute values of the scale-factor differences;

means for extracting information flags from the bit stream when it is decided that the bit stream is of the second format;

means for extracting selected-scale-factor data from the bit stream when it is decided that the bit stream is of the second format;

means for calculating second scale factors of the respective sub-band groups on the basis of the extracted information flags and the extracted selected-scale-factor data;

means for deriving first sub-band signals in the respective sub-bands from the bit stream in response to the first scale factors or the second scale factors;

means for inversely quantizing the first sub-band signals into second sub-band signals in response to the first scale factors or the second scale factors; and

means for combining the second sub-band signals into an original digital audio signal.