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Method for reduction of aliasing introduced by spectral envelope adjustment in real-valued filterbanks

  • US 10,115,405 B2
  • Filed: 10/31/2017
  • Issued: 10/30/2018
  • Est. Priority Date: 09/18/2002
  • Status: Expired due to Term
First Claim
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1. An audio decoder for producing a full bandwidth audio signal having a lowband portion and a highband portion, the apparatus comprising:

  • a cosine modulated, real-valued analysis filterbank that receives a time domain decoded audio signal and produces a plurality of real-valued subband signals;

    a high frequency reconstructor that regenerates at least some of the highband portion by copying one or more of the plurality of real-valued subband signals up to the highband portion;

    an aliasing detector that identifies subband signals where aliasing created by spectral envelope adjustment of an audio signal may occur based at least in part on a linear predictor applied to at least some of the plurality of real-valued subband signals;

    an energy estimator that estimates an energy of at least some of the plurality of copied real-valued subband signals;

    an aliasing reducer that modifies a gain to be applied to at least some of the identified subbands signals based at least in part on the estimated energy; and

    a real-valued synthesis filterbank that combines the plurality of real-valued subband signals with the highband portion to produce the full bandwidth audio signal, the full bandwidth audio including real-valued time domain samples,wherein the audio decoder is implemented at least in part with one of more hardware elements,wherein the linear predictor uses a covariance method of linear predictive coding (LPC),wherein the linear predictor is a second order linear predictor, andwherein the aliasing detector further comprises a subband examiner that examines subbands having channel numbers k and k−

    1.

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