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Methods and apparatus for post-filtering MDCT domain audio coefficients in a decoder

  • US 9,858,939 B2
  • Filed: 05/10/2011
  • Issued: 01/02/2018
  • Est. Priority Date: 05/11/2010
  • Status: Active Grant
First Claim
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1. A method of operating a decoder comprising:

  • obtaining a vector d(k) comprising quantized Modified Discrete Cosine Transform (MDCT) domain coefficients of a time segment of an audio signal;

    deriving a processed vector {circumflex over (d)}(k) by applying a post-filter directly on the vector d(k), the post-filter being configured to have a transfer function H(k),
    H(k)={(abs[d(k)])/(max[abs(d)])}a(k),which is a compressed version of an envelope of the vector d(k), where k goes from 1 to the number of MDCT domain coefficients of the time segment of the audio signal, where max[abs(d)] is a maximum of an absolute value of the vector d(k), and a(k) is an emphasis component configured to control a post-filter aggressiveness over the MDCT spectrum; and

    deriving a signal waveform by performing an inverse MDCT transform on the processed vector {circumflex over (d)}(k).

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