Polyphonic coding

Details Polyphonic coding Polyphonic coding

1993-08-20

1995-07-18

MacDonald, Allen R.

Electrical audio signal processing systems and devices

Hearing aids, electrical

Specified casing or housing

395 2, 395 21, 395 267, 381 51, G10L 900

Patent

active

054349486

ABSTRACT:
A polyphonic (e.g. stereo) audioconferencing system, in which input left and right channels are time-aligned by variable delay stages (10a, 10b), controlled by a delay calculator (9) (e.g. by deriving the maximum cross-correlation value), and then summed in an adder (2) and subtracted in subtracter (3) to form sum and difference signals. The sum signal is transmitted in relatively high quality; the difference signal is reconstructed at the decoder by prediction from the sum signal using an adaptive filter (5). The decoder adaptive filter (5) is configured either by received filter coefficients or, using backwards adaptation, from a received residual signal produced by a corresponding adaptive filter (4) in the coder, or both. Preferably, the adaptive filter (4) is a lattice filter, employing a gradient algorithm for coefficient update. The complexity of the adaptive filter (4) is reduced by pre-whitening, in the encoder, both the sum and difference signals using corresponding whitening filters (14a, 14b) derived from the sum channel.

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