Multichannel audio extension

• US 20050267763A1
• Filed: 05/26/2005
• Published: 12/01/2005
• Est. Priority Date: 05/28/2004
• Status: Active Grant

• Current Assignee: Nokia Corporation
• Original Assignee: Nokia Corporation
• Inventors: Ojanpera, Juha
• Granted Patent: US 7,620,554 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• CPC Class Codes: G10L 19/008 Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing
• CPC Class Codes: G10L 19/0204 using subband decomposition

Abstract

A method is shown for supporting a multichannel audio extension at an encoding end of a multichannel audio coding system. In order to improve the audio quality over a large frequency range, the method comprises transforming each channel of a multichannel audio signal into the frequency domain and dividing a bandwidth of the frequency domain signals into a first region of lower frequencies and at least one further region of higher frequencies. Then, the frequency domain signals are encoded in each of the frequency regions with another type of coding to obtain parametric multichannel extension information for the respective frequency region. The invention relates equally to a method for supporting in a corresponding manner a multichannel audio extension at a decoding end. Also shown are a corresponding encoder, a corresponding decoder, and corresponding devices, systems and software program products.

Claims

1. Method for supporting a multichannel audio extension at an encoding end (20) of a multichannel audio coding system, said method comprising:

transforming each channel of a multichannel audio signal into the frequency domain;

dividing a bandwidth of said frequency domain signals into a first region of lower frequencies and at least one further region of higher frequencies; and

encoding said frequency domain signals in each of said frequency regions with another type of coding to obtain a parametric multichannel extension information for the respective frequency region.

2. Method according to claim 1, wherein encoding said frequency domain signals in said first region comprises combining corresponding samples of all channels in said first region, quantizing said combined samples and encoding said quantized samples.

3. Method according to claim 2, wherein encoding said quantized samples comprises dividing said quantized samples into subblocks and encoding each subblock separately.

4. Method according to claim 2, wherein encoding said quantized samples comprises applying a plurality of coding schemes to said quantized samples and selecting a coding scheme which results in a lowest number of bits for said parametric multichannel extension information.

5. Method according to claim 4, wherein said plurality of coding schemes comprise a plurality of Huffman coding schemes.

6. Method according to claim 2, wherein, in case encoding said quantized samples results in more bits for said parametric multichannel extension information than are available for said first region, said quantization comprises modifying said quantized samples to obtain quantized samples which result in said encoding of quantized samples at the most in the number of bits for said parametric multichannel extension information that are available for said first region.

7. Method according to claim 2, wherein said quantization employs a selectable quantization gain for quantizing combined samples of a respective frame, said quantization comprising selecting a quantization gain for a respective frame which avoids sudden changes in the quantization gain from one frame to the next.

8. Method according to claim 2, wherein in case encoding said quantized samples results in a number of bits for said parametric multichannel extension information which is lower than a number of bits which are available for said first region, said method further comprising generating refinement bits representing information which allows to compensate for quantization errors.

9. Method according to claim 1, wherein said at least one further region comprises a middle frequency region and a high frequency region.

10. Method according to claim 9, wherein said type of coding employed for encoding said frequency domain signals in said middle frequency region comprises:

determining for each of a plurality of adjacent frequency bands within said middle frequency region whether a spectral first channel signal of said multichannel signal, a spectral second channel signal of said multichannel signal or none of said spectral channel signals is dominant in the respective frequency band; and

encoding a corresponding state information for each of said frequency bands as a parametric multichannel extension information.

11. Method according to claim 10, further comprising post-processing said determined state information such that short-time changes in said state information are avoided before encoding said state information.

12. Method according to claim 9, wherein said type of coding employed for encoding said frequency domain signals in said high frequency region comprises:

determining for each of a plurality of adjacent frequency bands within said high frequency region whether a spectral first channel signal of said multichannel signal, a spectral second channel signal of said multichannel signal or none of said spectral channel signals is dominant in the respective frequency band; and

selecting a first approach or a second approach for encoding a corresponding state information for each of said frequency bands as a parametric multichannel extension information, wherein said first approach includes encoding a corresponding state information for each of said frequency bands, and wherein said second approach includes comparing said state information for a current frame to state information for a previous frame, encoding a result of this comparison and encoding state information for a current frame only in case there was a change in said state information from said previous frame to said current frame.

13. Method according to claim 12, further comprising post-processing said determined state information such that short-time changes in said state information are avoided before encoding said state information.

14. Method for supporting a multichannel audio extension at a decoding end (21) of a multichannel audio coding system, said method comprising:

decoding an encoded parametric multichannel extension information which is provided separately for a first region of lower frequencies and for at least one further region of higher frequencies using different types of coding;

reconstructing a multichannel signal out of an available mono signal based on said decoded parametric multichannel extension information separately for said first region and said at least one further region;

combining said reconstructed multichannel signals in said first and said at least one further region; and

transforming each channel of said combined multichannel signal into the time domain.

15. Encoder (20) for supporting a multichannel audio extension at an encoding end of a multichannel audio coding system, said encoder (20) comprising:

a transforming portion (30,31) adapted to transform each channel of a multichannel audio signal into the frequency domain;

a separation portion (32) adapted to divide a bandwidth of frequency domain signals provided by said transforming portion (30,31) into a first region of lower frequencies and at least one further region of higher frequencies;

a low frequency encoder (35) adapted to encode frequency domain signals provided by said separation portion (32) for said first frequency region with a first type of coding to obtain a parametric multichannel extension information for said first frequency region; and

at least one higher frequency encoder (33,34) adapted to encode frequency domain signals provided by said separation portion (32) for said at least one further frequency region with at least one further type of coding to obtain a parametric multichannel extension information for said at least one further frequency region.

16. Encoder (20) according to claim 15, wherein said low frequency encoder (35) comprises a combining portion (51) adapted to combine corresponding samples of all channels in said first region, a quantization portion (52) adapted to quantize combined samples provided by said combining portion (51) and an encoding portion (53) adapted to encode quantized samples provided by said quantization portion (52).

17. Encoder (20) according to claim 16, wherein the encoding portion (53) is adapted to divide said quantized samples into subblocks and to encode each subblock separately.

18. Encoder (20) according to claim 16, wherein the encoding portion (53) is adapted apply a plurality of coding schemes to said quantized samples and to select a coding scheme which results in the lowest number of bits for said parametric multichannel extension information.

19. Encoder (20) according to claim 18, wherein said plurality of coding schemes comprise a plurality of Huffman coding schemes.

20. Encoder (20) according to claim 16, wherein said quantization portion (52) is adapted to modifying said quantized samples, in case encoding said quantized samples by said encoding portion (53) results in more bits for said parametric multichannel extension information than are available for said first region, to obtain quantized samples which result in said encoding of quantized samples by said encoding portion (53) at the most in the number of bits for said parametric multichannel extension information that are available for said first region.

21. Encoder (20) according to claim 16, wherein said quantization portion (52) is adapted to employ a selectable quantization gain for quantizing combined samples of a respective frame, and wherein said quantization portion (52) is further adapted to select a quantization gain for a respective frame which avoids sudden changes in the quantization gain from one frame to the next.

22. Encoder (20) according to claim 16, wherein said low frequency encoder (35) further comprises a refinement portion (54) which is adapted to generate refinement bits representing information which allows to compensate for quantization errors in a quantization by said quantization portion (52), in case encoding said quantized samples by said encoding portion (53) results in a number of bits for said parametric multichannel extension information which is lower than a number of bits which are available for said first region.

23. Encoder (20) according to claim 15, wherein said at least one higher frequency encoder (33,34) comprises a middle frequency encoder (34) adapted to encode frequency domain signals in a middle frequency region and a high frequency encoder (33) adapted to encode frequency domain signals in a high frequency region.

24. Encoder (20) according to claim 23, wherein said middle frequency encoder (34) comprises:

a processing portion (41) adapted to determine for each of a plurality of adjacent frequency bands within said middle frequency region whether a spectral first channel signal of said multichannel signal, a spectral second channel signal of said multichannel signal or none of said spectral channel signals is dominant in the respective frequency band and to provide for each frequency band a corresponding state information; and

an encoding portion (45) adapted to encode state information provided by said processing portion (41) to obtain a parametric multichannel extension information.

25. Encoder (20) according to claim 24, further comprising a post-processing portion (44) adapted to post-process state information determined by said processing portion (41) such that short-time changes in said state information are avoided before said state information is encoded by said encoding portion (45).

26. Encoder (20) according to claim 23, wherein said high frequency encoder (33) comprises:

a processing portion (41) adapted to determine for each of a plurality of adjacent frequency bands within said middle frequency region whether a spectral first channel signal of said multichannel signal, a spectral second channel signal of said multichannel signal or none of said spectral channel signals is dominant in the respective frequency band and to provide for each frequency band a corresponding state information; and

an encoding portion (45) adapted to select and to apply a first approach or a second approach for encoding a state information provided by said processing portion (41) to obtain a parametric multichannel extension information, wherein said first approach includes encoding a state information for each of said frequency bands provided by said processing portion (41), and wherein said second approach includes comparing state information provided by said processing portion (41) for a current frame to state information provided by said processing portion (41) for a previous frame, encoding a result of this comparison and encoding state information for a current frame only in case there was a change in said state information from said previous frame to said current frame.

27. Encoder (20) according to claim 26, further comprising a post-processing portion (44) adapted to post-process state information determined by said processing portion (41) such that short-time changes in said state information are avoided before said state information is encoded by said encoding portion (45).

29. Electronic device comprising an encoder (20) according to claim 15.

31. Audio coding system comprising a first electronic device with an encoder (20) according to claim 15 and a second electronic device with a decoder (21) for supporting a multichannel audio extension at a decoding end of a multichannel audio coding system, said decoder (21) comprising a processing portion (29) which is adapted to process encoded parametric multichannel extension information provided separately for a first region of lower frequencies and for at least one further region of higher frequencies, said processing portion (29) including:

a first decoding portion (65) adapted to decode an encoded parametric multichannel extension information which is provided for said first region using a first type of coding, and to reconstruct a multichannel signal out of an available mono signal based on said decoded parametric multichannel extension information;

at least one further decoding portion (63,64) adapted to decode an encoded parametric multichannel extension information which is provided for said at least one further region using at least one further type of coding, and to reconstruct a multichannel signal out of an available mono signal based on said decoded parametric multichannel extension information;

a combining portion (62) adapted to combine reconstructed multichannel signals provided by said first decoding portion (65) and said at least one further decoding portion (63,64); and

a transforming portion (60,61) adapted to transform each channel of a combined multichannel signal into a time domain.

28. Decoder (21) for supporting a multichannel audio extension at a decoding end of a multichannel audio coding system, said decoder (21) comprising a processing portion (29) which is adapted to process encoded parametric multichannel extension information provided separately for a first region of lower frequencies and for at least one further region of higher frequencies, said processing portion (29) including:

a first decoding portion (65) adapted to decode an encoded parametric multichannel extension information which is provided for said first region using a first type of coding, and to reconstruct a multichannel signal out of an available mono signal based on said decoded parametric multichannel extension information;

at least one further decoding portion (63,64) adapted to decode an encoded parametric multichannel extension information which is provided for said at least one further region using at least one further type of coding, and to reconstruct a multichannel signal out of an available mono signal based on said decoded parametric multichannel extension information;

a combining portion (62) adapted to combine reconstructed multichannel signals provided by said first decoding portion (65) and said at least one further decoding portion (63,64); and

a transforming portion (60,61) adapted to transform each channel of a combined multichannel signal into a time domain.

30. Electronic device comprising a decoder (21) according to claim 28.

32. Software program product in which a software code for supporting a multichannel audio extension at an encoding end (20) of a multichannel audio coding system is stored, said software code realizing the following steps when running in a processing component of an encoder (20)

transforming each channel of a multichannel audio signal into the frequency domain;

dividing a bandwidth of said frequency domain signals into a first region of lower frequencies and at least one further region of higher frequencies; and

encoding said frequency domain signals in each of said frequency regions with another type of coding to obtain a parametric multichannel extension information for the respective frequency region.

33. Software program product in which a software code for supporting a multichannel audio extension at an decoding end (21) of a multichannel audio coding system is stored, said software code realizing the following steps when running in a processing component of a decoder (21):

decoding an encoded parametric multichannel extension information which is provided separately for a first region of lower frequencies and for at least one further region of higher frequencies;

reconstructing a multichannel signal out of an available mono signal based on said decoded parametric multichannel extension information separately for said first region and said at least one further region;

combining said reconstructed multichannel signals in said first and said at least one further region; and

transforming each channel of said combined multichannel signal into the time domain.