Efficient and scalable parametric stereo coding for low bitrate applications

• US 20050053242A1
• Filed: 07/10/2002
• Published: 03/10/2005
• Est. Priority Date: 07/10/2001
• Status: Active Grant

• Current Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Original Assignee: Coding Technologies AB
• Inventors: Engdegard, Jonas, Roden, Jonas, Liljeryd, Lars, Kjorling, Kristofer, Henn, Fredrik
• Granted Patent: US 7,382,886 B2
• Time in Patent Office: Days
• US Class Current: 381/22
• 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
• CPC Class Codes: G10L 19/24 Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding
• CPC Class Codes: H04S 1/007 in which the audio signals are in digital form data reduction aspects thereof based on psychoacoustics G10L19/02
• CPC Class Codes: H04S 3/002 Non-adaptive circuits, e.g. manually adjustable or static, for enhancing the sound image or the spatial distribution control circuits for electronic adaptation of the sound field H04S7/30

Abstract

The present invention provides improvements to prior art audio codecs that generate a stereo-illusion through post-processing of a received mono signal. These improvements are accomplished by extraction of stereo-image describing parameters at the encoder side, which are transmitted and subsequently used for control of a stereo generator at the decoder side. Furthermore, the invention bridges the gap between simple pseudo-stereo methods, and current methods of true stereo-coding, by using a new form of parametric stereo coding. A stereo-balance parameter is introduced, which enables more advanced stereo modes, and in addition forms the basis of a new method of stereo-coding of spectral envelopes, of particular use in systems where guided HFR (High Frequency Reconstruction) is employed. As a special case, the application of this stereo-coding scheme in scalable HFR-based codecs is described.

Claims

1. A method for coding of stereo properties of an input signal, characterised by:

at an encoder, calculate a width-parameter that signals a stereo-width of said input signal, and

at a decoder, generate a stereo output signal, using said width-parameter to control a stereo-width of said output signal.

2. A method according to claim 1, characterised by:

at said encoder, form a mono signal from said input signal, and

at said decoder, said generation implies a pseudo-stereo method operating on said mono signal.

3. A method according to claim 2, characterised in that said pseudo-stereo method implies splitting of said mono signal into two signals as well as addition of delayed version(s) of said mono signal to said two signals, at level(s) controlled by said width-parameter.

4. A method according to claim 3, characterised in that said delayed version(s) are high-pass filtered and progressively attenuated at higher frequencies prior to being added to said two signals.

5. A method according to claim 1, characterised in that said width-parameter is a vector, and the elements of said vector correspond to separate frequency bands.

6. A method according to claims 1-5, characterised in that if said input signal is of type dual mono, said output signal is also of type dual mono.

24. A method according to any of claims 2 and 8, characterised in that said input signal is passed though a Hilbert transformer prior to forming said mono signal.

7. A method for coding of stereo properties of an input signal, characterised by:

at an encoder, calculate a balance-parameter that signals a stereo-balance of said input signal, and

at a decoder, generate a stereo output signal, using said balance-parameter to control a stereo-balance of said output signal.

8. A method according to claim 7, characterised by:

at said encoder, form a mono signal from said input signal, and

at said decoder, said generation implies splitting of said mono signal into two signals, and said control implies adjustment of levels of said two signals.

9. A method according to claim 7, characterised in that a power for each channel of said input signal is calculated, and said balance-parameter is calculated from a quotient between said powers.

10. A method according to claim 9, characterised in that said powers and said balance-parameter are vectors where every element corresponds to a specific frequency band.

11. A method according to claim 7, characterised in at said decoder interpolating between two in time consequtive values of said balance-parameters in a way that the momentary value of the corresponding power of said mono signal controls how steep the momentary interpolation should be.

12. A method according to claim 11, characterised in that said interpolation method is performed on balance values represented as logarithmic values.

13. A method according to claim 7, characterised in that said values of balance-parameters are limited to a range between a previous balance value, and a balance value extracted from other balance values by a median filter or other filter process, where said range can be further extended by moving the borders of said range by a certain factor.

14. A method according to claim 13, characterised in that said method of extracting limiting borders for balance values, is, for a multiband system, frequency dependent.

15. A method according to claim 10, characterised in that an additional level-parameter is calculated as a vector sum of said powers and sent to said decoder, thereby providing said decoder a representation of a spectral envelope of said input signal.

16. A method according to claim 15, characterised in that said level-parameter and said balance-parameter adaptively are replaced by said powers.

17. A method according to claim 16, characterised in that said spectral envelope is used to control a HFR-process in a decoder.

18. A method according to claim 15, characterised in that said level-parameter is fed into a primary bitstream of a scalable HFR-based stereo codec, and said balance-parameter is fed into a secondary bitstream of said codec.

19. A method according to claims 2 and 18, characterised in that said mono signal and said width-parameter are fed into said primary bitstream.

20. A method according to claims 5 and 16, characterised in that said width-parameters are processed by a function that gives smaller values for a balance value that corresponds to a balance position further from the center position.

21. A method according to any of claims 7-18, characterised in that a quantization of said balance-parameter employs smaller quantization steps around a center position and larger steps towards outer positions.

22. A method according to claims 5 and 21, characterised in that said width-parameters and said balance-parameters are quantized using a quantization method in terms of resolution and range which, for a multiband system, is frequency dependent.

23. A method according to any of claims 10-18, characterised in that said balance-parameter adaptively is delta-coded either in time or in frequency.

25. An apparatus for parametric stereo coding, characterised by:

at an encoder, means for calculation of a width-parameter that signals a stereo-width of an input signal, and means for forming a mono signal from said input signal,

at a decoder, means for generating a stereo output signal from said mono signal, using said width-parameter to control a stereo-width of said output signal.