Vector-space methods for primary-ambient decomposition of stereo audio signals

1. A method for processing a multichannel audio signal to determine primary and ambient components of the signal, the method comprising:

converting each channel of the multichannel audio signal to corresponding subband vectors, wherein the vectors comprise a time sequence or history of the channel signal's behavior in corresponding subbands;

determining, using at least one processor, a primary component unit vector for each subband by a principal component analysis; and

determining primary component vectors for each audio channel in each subband by projecting the channel subband vector onto the primary component unit vector; and

determining the ambience component vector for each channel in each frequency subband as the projection residual; and

generating the primary and ambience components from the respective primary and ambience component vectors.

2. The method as recited in claim 1 further comprising computing a correlation matrix corresponding to the left and right channel subband data;

determining at least a dominant eigenvalue and corresponding eigenvector for the correlation matrix; and

wherein the primary component vector is determined at least in part from the dominant eigenvalue or the corresponding eigenvector.

3. The method as recited in claim 1 further comprising performing an allpass filtering operation on the extracted ambient signal for distributing the processed signals to the surround speakers in a multichannel rendering.

4. A method for determining primary and ambient components of a signal, the method comprising:

converting for each subband left and right channels of the audio signal to corresponding frequency-domain vectors; and

decomposing using at least one processor the left and right channel vectors into ambient and primary components by cross-channel orthogonal projection for determining the ambience in the right channel as orthogonal to the left channel vector and the ambience in the left channel as orthogonal to the right channel vector.

5. The method as recited in claim 4 wherein the primary component for at least one channel is determined by the residual in the signal after the ambience is determined.

6. The method as recited in claim 4 wherein the ambience components for the respective left and right channels are subsequently scaled with equal weights and the primary components for the left and right channels are determined by the difference between the respective channel signal and the corresponding rescaled ambience.

7. The method as recited in claim 4 wherein the magnitudes of the ambient components for the left and right channels are scaled to be equal to each other and the primary components are determined by the difference between the respective channel signal and the corresponding rescaled ambience.

8. The method as recited in claim 4 wherein the magnitudes of the ambient components for the left and right channels are scaled such that the ambient signals for the respective channels contain equal energy and the primary components are determined by the difference between the respective channel signal and the corresponding rescaled ambience.

9. The method as recited in claim 4 further comprising performing an allpass filtering operation on the extracted ambient signal for distributing the processed signals to the surround speakers in a multichannel rendering.

10. The method as recited in claim 4 further comprising extracting a center channel from the derived primary component(s).

11. A method for determining primary and ambient components of at least a two channel signal having respective channels x L and x R , the method comprising:

determining vectors v L and v R,

orthogonally projecting using at least one processor the originals x L and x R onto those respective vectors to determine the primary components of the original signal; and

determining the ambience as the projection residual.

12. The method as recited in claim 11 wherein v L and v R comprise a common vector for the left and right channels and the common vector is determined as the principal eigenvector determined by principal component analysis.

13. The method as recited in claim 11 wherein v L is equal to or a scaled version of x R and v R is equal to or a scaled version of x L and v L and v R are determined by cross-channel projection.

14. A system for processing a multichannel audio signal having at least two channels to determine primary and ambient components of the signal, comprising:

a conversion module for converting each channel of the multichannel audio signal to corresponding subband vectors, wherein the vectors comprise a time sequence or history of the channel signal's behavior in corresponding subbands;

at least one processor configured to determine a primary component unit vector for each subband by a principal component analysis; to determine primary component vectors for each audio channel in each subband by projecting the channel subband vector onto the primary component unit vector; and to determine the ambience component vector for each channel in each frequency subband as the projection residual; and

a module for generating the primary and ambience components from the respective primary and ambience component vectors.