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Quality improvement techniques in an audio encoder

  • US 7,917,369 B2
  • Filed: 04/18/2007
  • Issued: 03/29/2011
  • Est. Priority Date: 12/14/2001
  • Status: Expired due to Fees
First Claim
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1. In a transform-based audio encoder, a method of improved band truncation, the method comprising:

  • performing a frequency transform on each of multiple input channels of a multi-channel input audio signal to produce multiple input channels of transform domain coefficients;

    performing a multi-channel transformation on the multiple input channels of transform domain coefficients for the multi-channel input audio signal to produce a plurality of joint coding channels;

    on a channel-by-channel basis, selectively suppressing at least one of the joint coding channels as a function of at least quality of reproduction, rate control buffer fullness, and channel separation, wherein the selectively suppressing comprises scaling the at least one joint coding channel by a scaling factor having a value varying based on a current average level of quality, current rate control buffer fullness and amount of channel separation; and

    for at least one of the joint coding channels;

    selecting as an open-loop process a first portion of the transform domain coefficients for band truncation as a function of a target quality measurement;

    suppressing the selected first portion of the transform domain coefficients from encoding in a compressed audio data stream;

    measuring an achieved quality measurement of the input audio signal encoded with the selected first portion of the transform domain coefficients suppressed;

    selecting as a closed-loop process a second portion of the transform domain coefficients for second band truncation as a function of the achieved quality measurement; and

    suppressing the selected second portion of the transform domain coefficients from encoding in a second compressed audio data stream.

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