METHOD AND APPARATUS TO ENCODE/DECODE LOW BIT-RATE AUDIO SIGNAL

• US 20070016411A1
• Filed: 07/12/2006
• Published: 01/18/2007
• Est. Priority Date: 07/15/2005
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Kim, Junghoe, Oh, Eunmi, Kudryashov, Boria, Osipoy, Koostantin
• Granted Patent: US 8,301,439 B2
• Time in Patent Office: Days
• US Class Current: 704/226
• CPC Class Codes: G10L 19/0017 Lossless audio signal coding; Perfect reconstruction of coded audio signal by transmission of coding error G10L19/24 takes precedence
• CPC Class Codes: G10L 19/02 using spectral analysis, e.g. transform vocoders or subband vocoders
• CPC Class Codes: G10L 19/06 Determination or coding of the spectral characteristics, e.g. of the short-term prediction coefficients

Abstract

A method and apparatus to encode/decode a low bit-rate audio signal. The method of encoding a low bit-rate audio signal, includes quantizing and losslessly-encoding a specific frequency component of an audio signal in a frequency domain, generating codebooks using the audio signal in the frequency domain, detecting an envelope of a frequency component of the audio signal other than the specific frequency component in a specific band unit and quantizing and losslessly-encoding the detected envelope of the other frequency component, selecting a codebook that is most similar to the other frequency component of the audio signal to be encoded from among the generated codebooks and determining a codebook index (fine structure), losslessly-encoding the determined codebook index, and generating a bit stream using the specific frequency component, the envelope of the other frequency component, and the determined codebook index. The method of decoding a low bit-rate audio signal, includes restoring and dividing a bit stream into a specific frequency component and a frequency component other than the specific frequency component, losslessly-decoding and inversely quantizing the specific frequency component, restoring codebook index information and envelope information about the other frequency component, generating codebooks using the specific frequency component which is inversely quantized, and restoring the other frequency component using the restored codebook index information and the restored envelope information about the other frequency component.

Claims

1. A method of encoding a low bit-rate audio signal, the method comprising:

quantizing and losslessly-encoding a specific frequency component of an audio signal in a frequency domain;

generating codebooks using the audio signal in the frequency domain;

detecting an envelope of a frequency component of the audio signal other than the specific frequency component in a specific band unit and quantizing and losslessly-encoding the envelope;

selecting a codebook that is most similar to the other frequency component to be encoded from the codebooks and determining a codebook index (fine structure);

losslessly-encoding the determined codebook index; and

generating a bit stream using losslessly-encoded data generated in the lossless-encoding of the specific frequency component, the envelope, and the determined codebook index.

2. The method of claim 1, wherein the specific frequency component is an important spectral component (ISC).

3. The method of claim 1, wherein the quantizing and lossless-encoding of the specific frequency component is one of an MPEG1 layer 3 coding (mp3) and an MPEG-2/4 advanced audio coding (AAC).

4. A method of encoding a low bit-rate audio signal, the method comprising:

quantizing and losslessly-encoding a significant frequency component of an audio signal in a frequency domain;

generating codebooks using the audio signal in the frequency domain;

detecting an envelope of a frequency component of the audio signal other than the significant frequency component in a specific band unit and quantizing and losslessly-encoding the detected envelope of the other frequency component;

checking whether a codebook having at least a predetermined similarity exists among the generated codebooks with respect to a high frequency band to be encoded;

if the similar codebook exists, selecting the similar codebook, determining a codebook index, and losslessly-encoding the determined codebook index and information indicating that the similar codebook exists;

if a similar codebook does not exist, losslessly-encoding information indicating that a similar codebook does not exist; and

generating a bit stream using losslessly-encoded data generated in the lossless encoding of the significant frequency component, the envelope of the other frequency component, the determined codebook index, and the information indicating that the similar codebook does not exist.

5. The method of claim 4, wherein the significant frequency component is a low frequency component.

6. The method of claim 4, wherein the high frequency band is a non-uniform band which takes hearing characteristics into consideration.

7. The method of claim 6, wherein the non-uniform band is a bark band.

8. The method of claim 4, wherein the codebooks are generated using overlapped spectra.

9. The method of claim 4, wherein the similarity is determined using a Euclidian distance or a correlation between the codebooks.

10. The method of claim 4, further comprising:

generating the audio signal in the frequency domain by converting an audio signal in a time domain to the audio signal in the frequency domain.

11. An apparatus to encode a low bit-rate audio signal, the apparatus comprising:

a low frequency quantizing/lossless-encoding unit which quantizes and losslessly-encodes a specific frequency component of an audio signal in a frequency domain;

a codebook generating unit which generates codebooks using the audio signal in the frequency domain;

an envelope quantizing/lossless-encoding unit which detects an envelope of a frequency component of the audio signal other than the specific frequency component in a specific band unit and quantizes and losslessly-encodes the detected envelope of the other frequency component;

a codebook index acquiring unit which selects a codebook most similar to the other frequency component to be encoded from among the generated codebooks and determines a codebook index (fine structure);

an index lossless-encoding unit which losslessly-encodes the determined codebook index; and

a bit stream generating unit which generates a bit stream using losslessly encoded data which are generated by the low frequency quantizing/lossless-encoding unit, the envelope quantizing/lossless-encoding unit, and the index lossless-encoding unit.

12. The apparatus of claim 11, wherein the specific frequency component is an important spectral component (ISC).

13. The apparatus of claim 11, wherein the low frequency quantizing/lossless-encoding unit quantizes and losslessly encodes using one of an MPEG1 layer 3 coding (mp3) and an MPEG-2/4 advanced audio coding (AAC).

14. An apparatus to encode a low bit-rate audio signal, the apparatus comprising:

a low frequency quantizing/lossless-encoding unit which quantizes and losslessly-encodes an important spectral component (ISC) of an audio signal in a frequency domain;

a codebook generating unit which generates codebooks using the audio signal in the frequency domain;

an envelope quantizing/lossless-encoding unit which detects an envelope of a frequency component of the audio signal other than the important spectral component in a specific band unit and quantizes and losslessly-encodes the detected envelope of the other frequency component;

a similarity checking unit which checks whether a codebook having at least a predetermined similarity exists among the generated codebooks with respect to a high frequency band to be encoded;

a codebook existence information/index encoding unit which selects a similar codebook, determines a codebook index if the similar codebook exists, and losslessly-encodes the determined codebook index and information indicating that the similar codebook exists;

a codebook existence information encoding unit which losslessly-encodes information indicating that a similar codebook does not exist if a similar codebook does not exist; and

a bitstream generating unit which generates a bit stream using losslessly encoded data which are generated by the low frequency quantizing/lossless-encoding unit, the codebook existence information/index encoding unit, and the codebook existence information encoding unit.

15. The apparatus of claim 14, wherein the important spectral component is a low frequency component.

16. The apparatus of claim 14, wherein the high frequency band is a non-uniform band which takes hearing characteristics into consideration.

17. The apparatus of claim 16, wherein the non-uniform band is a bark band.

18. The apparatus of claim 14, wherein the codebooks are generated using overlapped spectra.

19. The apparatus of claim 14, wherein the similarity is determined using a Euclidian distance or a correlation between the codebooks.

20. The apparatus of claim 14, further comprising:

a T/F converting unit which converts an audio signal in a time domain into the audio signal in the frequency domain.

21. An encoding apparatus, comprising:

a first quantizing/encoding unit to quantize a first frequency component of a full spectrum of an audio signal and to encode the quantized first frequency component;

a second quantizing/encoding unit to quantize one or more envelopes of one or more bands of a second frequency component of the full spectrum and to encode the quantized one or more envelopes;

a codebook unit to generate one or more codebooks from one or more bands of the first frequency component, to determine whether a similar codebook exists for each of the bands of the second frequency component, and to encode codebook similarity information to indicate similarities between the bands of the second frequency components and the codebooks; and

a bit stream unit to generate a bitstream including the encoded first frequency component, the encoded envelopes of the bands of the second frequency components, and the encoded similarity information.

22. The encoding apparatus of claim 21, wherein the second quantizing/encoding unit encodes the envelopes of the second frequency component using an adaptive vector quantization when the corresponding bands in the second frequency component are determined to be similar to ones of the codebooks, and encodes the envelopes of the second frequency component using a perceptual noise substitution when the corresponding bands in the second frequency component are determined not to be similar to any of the codebooks.

23. A method of decoding a low bit-rate audio signal, the method comprising:

restoring and dividing a bit stream into a specific frequency component and a frequency component other than the specific frequency component;

losslessly-decoding and inversely quantizing the specific frequency component;

restoring codebook index information and envelope information about the other frequency component;

generating codebooks using the inversely quantized specific frequency component; and

restoring the other frequency component using the restored codebook index information and the restored envelope information about the other frequency component.

24. The method of claim 23, wherein the specific frequency component is an important spectral component (ISC).

25. The method of claim 23, wherein the lossless-decoding and inverse quantizing of the specific frequency component is one of an MPEG1 layer 3 decoding (mp3) and an MPEG-2/4 advanced audio decoding (AAC).

26. A method of decoding a low bit-rate audio signal, the method comprising:

restoring and dividing a bit stream into a significant frequency component and a frequency component other than the significant frequency component;

losslessly-decoding and inversely quantizing the significant frequency component;

losslessly-decoding information as to whether a similar codebook exists;

if a similar codebook exists, restoring codebook index information and envelope information about the other frequency component;

generating codebooks using the significant frequency component which is lossless-decoded and inversely quantized and restoring a high frequency component using the restored codebook index information and the restored envelope information about the other frequency component; and

if a similar codebook does not exist, restoring the envelope information and restoring the other frequency component using a signal of a previous band and the restored envelope information.

27. The method of claim 26, wherein the significant frequency component is a low frequency component.

28. The method of claim 26, wherein the previous band is a non-uniform band which takes hearing characteristics into consideration.

29. The method of claim 28, wherein the non-uniform band is a bark band.

30. The method of claim 26, wherein the codebooks are generated using overlapped spectra.

31. The method of claim 26, wherein the similarity is determined using a Euclidian distance or a correlation between the codebooks.

32. The method of claim 26, further comprising:

generating the audio signal by inversely converting an audio signal in a frequency domain into an audio signal in a time domain.

33. An apparatus to decode a low bit-rate audio signal, the apparatus comprising:

a bit stream dividing unit which restores and divides a bit stream into a specific frequency component and a frequency component other than the specific frequency component;

a low frequency restoring unit which losslessly-decodes and inversely quantizes the specific frequency component;

a high frequency index/envelope restoring unit which restores codebook index information and envelope information about the other frequency component;

a codebook generating unit which generates codebooks using the specific frequency component inversely quantized in the low frequency restoring unit; and

a high frequency restoring unit which restores the other frequency component using the restored codebook index information and the restored envelope information about the other frequency component.

34. The apparatus of claim 33, wherein the specific frequency component is an important spectral component (ISC).

35. The apparatus of claim 33, wherein the quantizing and lossless decoding and inverse quantization is one of an MPEG1 layer 3 decoding (mp3) and an MPEG-2/4 advanced audio decoding (AAC).

36. An apparatus to decode a low bit-rate audio signal, the apparatus comprising:

a bit stream dividing unit which restores and divides a bit stream into a significant frequency component and a frequency component other than the specific frequency component;

a low frequency restoring unit which losslessly decodes and inversely quantizes the significant frequency component;

a codebook existence information restoring unit which losslessly decodes information as to whether a similar codebook exists;

an index/envelope restoring unit which, if the similar codebook exists, restores codebook index information and envelope information about the other frequency component;

a first high frequency restoring unit which generates codebooks using the significant frequency component which is losslessly-decoded and inversely quantized and restores a high frequency component using the restored codebook index information and the restored envelope information about the other frequency component; and

a second high frequency restoring unit which, if a similar codebook does not exist, restores the envelope information and restores the other frequency component using a signal of a previous band and the restored envelope information.

37. The apparatus of claim 36, wherein the significant frequency component is a low frequency component.

38. The apparatus of claim 36, wherein the previous band is a non-uniform band which takes hearing characteristics into consideration.

39. The apparatus of claim 38, wherein the non-uniform band is a bark band.

40. The apparatus of claim 36, wherein the codebooks are generated using overlapped spectra.

41. The apparatus of claim 36, wherein the similarity is determined using a Euclidian distance or a correlation between the codebooks.

42. The apparatus of claim 36, further comprising:

an F/T converting unit which inversely converts the audio signal from an audio signal in a frequency domain into an audio signal in a time domain.

43. A computer-readable medium having a computer program to execute a method of encoding a low bit-rate audio signal, the method comprising:

quantizing and losslessly-encoding a specific frequency component of an audio signal in a frequency domain;

generating codebooks using the audio signal in the frequency domain;

detecting an envelope of a frequency component of the audio signal other than the specific frequency component in a specific band unit and quantizing and losslessly-encoding the envelope;

selecting a codebook that is most similar to the other frequency component to be encoded from the codebooks and determining a codebook index (fine structure);

losslessly-encoding the determined codebook index; and

generating a bit stream using losslessly-encoded data generated in the lossless-encoding of the specific frequency component, the envelope, and the determined codebook index.

44. A computer-readable medium having a computer program to execute a method of encoding a low bit-rate audio signal, the method comprising:

quantizing and losslessly-encoding a significant frequency component of an audio signal in a frequency domain;

generating codebooks using the audio signal in the frequency domain;

detecting an envelope of a frequency component of the audio signal other than the significant frequency component in a specific band unit and quantizing and losslessly-encoding the detected envelope of the other frequency component;

checking whether a codebook having at least a predetermined similarity exists among the generated codebooks with respect to a high frequency band to be encoded;

if the similar codebook exists, selecting the similar codebook, determining a codebook index, and losslessly-encoding the determined codebook index and information indicating that the similar codebook exists;

if a similar codebook does not exist, losslessly-encoding information indicating that a similar codebook does not exist; and

generating a bit stream using losslessly-encoded data generated in the lossless encoding of the significant frequency component, the envelope of the other frequency component, the determined codebook index, and the information indicating that the similar codebook does not exist.

45. A computer-readable medium having a computer program to execute a method of decoding a low bit-rate audio signal, the method comprising:

restoring and dividing a bit stream into a specific frequency component and a frequency component other than the specific frequency component;

losslessly-decoding and inversely quantizing the specific frequency component;

restoring codebook index information and envelope information about the other frequency component;

generating codebooks using the inversely quantized specific frequency component; and

restoring the other frequency component using the restored codebook index information and the restored envelope information about the other frequency component.

46. A computer-readable medium having a computer program to execute a method of decoding a low bit-rate audio signal, the method comprising:

restoring and dividing a bit stream into a significant frequency component and a frequency component other than the significant frequency component;

losslessly-decoding and inversely quantizing the significant frequency component;

losslessly-decoding information as to whether a similar codebook exists;

if a similar codebook exists, restoring codebook index information and envelope information about the other frequency component;

generating codebooks using the significant frequency component which is lossless-decoded and inversely quantized and restoring a high frequency component using the restored codebook index information and the restored envelope information about the other frequency component; and

if a similar codebook does not exist, restoring the envelope information and restoring the other frequency component using a signal of a previous band and the restored envelope information.