Support of a multichannel audio extension

• US 20040267543A1
• Filed: 04/28/2004
• Published: 12/30/2004
• Est. Priority Date: 04/30/2003
• Status: Active Grant

• Current Assignee: Nokia Corporation
• Original Assignee: Nokia Corporation
• Inventors: Ojanpera, Juha
• Granted Patent: US 7,627,480 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: H04S 1/007 in which the audio signals are in digital form data reduction aspects thereof based on psychoacoustics G10L19/02

Abstract

Methods and units supporting a multichannel audio extension in a multichannel audio coding system are shown. In order to allow an efficient extension of an available mono audio signal {tilde over (M)} of a multichannel audio signal L/R, it is proposed that an encoding end of the multichannel audio coding system provides dedicated multichannel extension information for lower frequencies of the multichannel audio signal L/R, in addition to multichannel extension information at least for higher frequencies of the multichannel audio signal L/R. This dedicated multichannel extension information enables a decoding end of the multichannel audio coding system to reconstruct the lower frequencies of the multichannel audio signal L/R with a higher accuracy than the higher frequencies of the multichannel audio signal L/R.

Claims

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

generating and providing first multichannel extension information at least for higher frequencies of a multichannel audio signal (L,R), which first multichannel extension information allows to reconstruct at least said higher frequencies of said multichannel audio signal (L,R) based on a mono audio signal ({tilde over (M)}) available for said multichannel audio signal (L,R); and

generating and providing second multichannel extension information for lower frequencies of said multichannel audio signal (L,R), which second multichannel extension information allows to reconstruct said lower frequencies of said multichannel audio signal (L,R) based on said mono audio signal ({tilde over (M)}) with a higher accuracy than said first multichannel extension information allows to reconstruct at least said higher frequencies of said multichannel audio signal (L,R).

2. Method according to claim 1, wherein generating and providing said second multichannel extension information comprises

transforming a first channel signal (L) of a multichannel audio signal into the frequency domain, resulting in a spectral first channel signal (L_f);

transforming a second channel signal (R) of said multichannel audio signal into the frequency domain, resulting in a spectral second channel signal (R_f);

generating a spectral side signal (S) representing the difference between said spectral first channel signal (L_f) and said spectral second channel signal (R_f);

quantizing said spectral side signal (S) to obtain a quantized spectral side signal;

encoding said quantized spectral side signal and providing said encoded quantized spectral side signal as part of said second multichannel extension information.

3. Method according to claim 2, wherein said quantizing comprises quantizing said spectral side signal (S) in a loop in which the quantizing gain is varied such that a quantized spectral side signal is obtained of which the maximum absolute value lies below a predetermined threshold value.

4. Method according to claim 3, wherein said predetermined threshold value is adjusted to ensure that said encoding of said quantized spectral side signal results in a number of bits which lies less than a predetermined number of bits below a number of available bits.

5. Method according to claim 3, further comprising setting all values of said quantized spectral side signal to zero, in case a quantizing gain (qGain) required for said obtained quantized spectral side signal lies below a second predetermined threshold value.

6. Method according to claim 2, further comprising setting all values of said quantized spectral side signal to zero, in case an average energy (tLevel) at said lower frequencies of said spectral first and second channel signals (L_f,R_f) lies below a predetermined threshold value.

7. Method according to claim 2, further comprising setting those values of said quantized spectral side signal to zero, which do not belong to a spectral environment providing a significant contribution to a multichannel image in said multichannel audio signal.

8. Method according to claim 2, wherein said encoding is based on a Huffman coding scheme.

9. Method according to claim 2, wherein said encoding comprises selecting one of at least two coding schemes, which selected coding scheme results for said quantized spectral side signal in the least number of bits.

10. Method according to claim 2, wherein said encoding comprises discarding at least the sample of said quantized spectral side signal having the lowest energy, in case encoding said entire quantized spectral side signal results in a number of bits exceeding a number of available bits.

11. Method according to claim 1, further comprising generating and providing an indication (hPanning) whether any channel (L,R) of said multichannel audio signal is considerably stronger at said lower frequencies of said multichannel audio signal than another channel (R,L) of said multichannel audio signal.

12. Method according to claim 1, wherein said first multichannel extension information is generated in a frequency domain on a frequency band basis and wherein said second multichannel extension information is generated in a frequency domain on a sample basis.

13. Method according to claim 1, comprising in addition

combining a first channel signal (L) and a second channel signal (R) of said multichannel audio signal to a mono audio signal (M) and encoding said mono signal (M) to a mono signal bitstream;

and

multiplexing at least said mono signal bitstream, said provided first multichannel extension information and said provided second multichannel extension information into a single bitstream.

20. Multichannel audio encoder (20) comprising means (202-207,30-32,321-327) for realizing the steps of the method of claim 1.

21. Multichannel extension encoder (206,207) for a multichannel audio encoder (20), said multichannel extension encoder (206,207) comprising means (30-32,321-327) for realizing the steps of the method of claim 1.

24. Multichannel audio coding system comprising an encoder (20) with means (202-207,30-32,321-327) for realizing the steps of the method of claim 1 and a decoder (21) with means (215-217, 40-44, 401-403) for realizing the following steps:

reconstructing at least higher frequencies of a multichannel audio signal (L,R) based on received first multichannel extension information for said multichannel audio signal and on a received mono audio signal ({tilde over (M)}) for said multichannel audio signal (L,R); and

reconstructing lower frequencies of said multichannel audio signal (L,R) based on received second multichannel extension information and on said received mono audio signal ({tilde over (M)}) with a higher accuracy than said higher frequencies; and

combining said reconstructed higher frequencies and said reconstructed lower frequencies to a reconstructed multichannel audio signal ({tilde over (L)}_tnew, {tilde over (R)}_tnew).

25. Method according to claim 4, further comprising setting all values of said quantized spectral side signal to zero in case a quantizing gain (qGain) required for said obtained quantized spectral side signal lies below a second predetermined threshold value.

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

reconstructing at least higher frequencies of a multichannel audio signal (L,R) based on received first multichannel extension information for said multichannel audio signal and on a received mono audio signal ({tilde over (M)}) for said multichannel audio signal (L,R); and

reconstructing lower frequencies of said multichannel audio signal (L,R) based on received second multichannel extension information and on said received mono audio signal ({tilde over (M)}) with a higher accuracy than said higher frequencies; and

combining said reconstructed higher frequencies and said reconstructed lower frequencies to a reconstructed multichannel audio signal ({tilde over (L)}_tnew, {tilde over (R)}_tnew).

15. Method according to claim 14, wherein reconstructing lower frequencies of said multichannel audio signal (L,R) comprises

decoding a quantized spectral side signal comprised in said second multichannel extension information;

dequantizing said quantized spectral side signal to obtain a dequantized spectral side signal; and

extending said received mono audio signal ({tilde over (M)}) with said dequantized spectral side signal to obtain reconstructed lower frequencies of a spectral first channel signal and of a spectral second channel signal of said multichannel audio signal (L,R).

16. Method according to claim 15, further comprising attenuating one of said spectral channel signals at said lower frequencies, in case said second multichannel extension information further comprises an indication that another one of said spectral channel signals was considerably stronger in said multichannel audio signal (L,R) which is to be reconstructed at said lower frequencies.

17. Method according to claim 14, wherein combining said reconstructed higher frequencies and said reconstructed lower frequencies is performed in a frequency domain to obtain reconstructed spectral channel signals ({tilde over (L)}_f, {tilde over (R)}_f) including higher and lower frequencies, and transforming said reconstructed spectral channel signals ({tilde over (L)}_f, {tilde over (R)}_f) into the time domain to obtained to said reconstructed multichannel audio signal ({tilde over (L)}_tnew, {tilde over (R)}_tnew).

18. Method according to claim 14, wherein said higher frequencies of said multichannel audio signal (L,R) are reconstructed in a frequency domain on a frequency band basis and wherein said lower frequencies of said multichannel audio signal (L,R) are reconstructed in a frequency domain on a sample basis.

19. Method according to claim 14, further comprising receiving a bitstream, and demultiplexing said bitstream to a first bitstream comprising said mono audio signal ({tilde over (M)}), a second bitstream comprising said first multichannel extension information and a third bitstream comprising said second multichannel extension information.

22. Multichannel audio decoder (21) comprising means (215-217,40-44,401-403) for realizing the steps of the method of claim 14.

23. Multichannel extension decoder (216,217) for a multichannel audio decoder (21), said multichannel extension decoder (216,217) comprising means (40-44,401-403) for realizing the steps of the method of claim 14.