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Method subband of coding and decoding audio signals using variable length windows

  • US 5,848,391 A
  • Filed: 07/11/1996
  • Issued: 12/08/1998
  • Est. Priority Date: 07/11/1996
  • Status: Expired due to Term
First Claim
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1. A method of encoding time-discrete audio signals including weighting the time-discrete audio signals by means of window functions overlapping each other so as to form blocks, said window functions comprising a first window function including a first half and a second half for producing blocks of a first length for signals varying weakly with time and a second window function including a first half and a second half for producing blocks of a second length for signals varying strongly with time, said method comprising:

  • applying said first window function, to said time-discrete audio signals to produce blocks of said first length;

    upon detecting signals varying strongly with time, applying one start window sequence from a plurality of different start window sequences to effect a transition from producing blocks of said first length to producing blocks of said second length, one of said start window sequences including a first part corresponding to said first half of said first window function, a second non-overlapping part having a length, a third part corresponding to said second half of said second window function, and a fourth part having at least one said overlapping second window function;

    upon detecting signals varying weakly with time, applying one stop window sequence from a plurality of different stop window sequences to effect a transition producing blocks of said second length to producing blocks of said first length, one of said stop window sequences comprising a first part having at least one overlapping second window function, a second part corresponding to said first half of said second window function;

    a third non-overlapping part having a length; and

    a fourth part corresponding to said second half of said first window function; and

    wherein, said length of said non-overlapping part and said overlapping second window functions are selected in a manner that a number of frequency coefficients obtained by a frequency transform of said time-discrete audio signals windowed by said start window sequence and said stop window sequence is equal to a number of frequency coefficients obtained by said frequency transform of time-discrete audio signals windowed by said first window function.

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