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

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;
• and
• upon detecting signals varying strongly with time, applying a start window sequence to effect a transition from producing blocks of said first length to producing blocks of said second length;
• said start window sequence 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;
• 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 is equal to a number of frequency coefficients obtained by said frequency transform of time-discrete audio signals windowed by said first window function.

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 second window function to said time-discrete audio signals to produce blocks of said second length;
• upon detecting signals varying weakly with time, applying a stop window sequence to effect a transition from producing blocks of said second length to producing blocks of said first length, said stop window sequence including a first part having at least one said 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;
• 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 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.

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:

• windowing said time-discrete audio signals by employing said first window function producing blocks of said first length;
• upon detecting transient signals applying a start window sequence to achieve a transition from windowing with blocks of said first length to windowing with blocks of said second length and
• subsequently applying a stop window sequence for an opposite transition,
• wherein said start or stop window sequence includes a segment having a non-overlapping length and another segment having a number of said second window functions being overlapped, said non-overlapping length and said number of 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.

A method of decoding time-discrete audio signals encoded in blocks, said method comprising the following steps:

• reading of side information with which said encoded blocks are provided, said side information referring to a first or second window function, a start window sequence or a stop window sequence which has been used in connection with the block in question and to the transform which has been used with the block in question, wherein said start or stop window sequence includes a segment having a non-overlapping length and another segment having a number of said second window functions being overlapped, said non-overlapping length and said number of 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;
• selecting an inverse transform and a synthesis window function as a reaction to the side information read;
• and
• re-transforming and windowing with the selected inverse transform and the selected synthesis window function.

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 the steps of:

• windowing said time-discrete audio signals by employing said first window function producing blocks of said first length;
• upon detecting signals varying strongly with time, selecting a start window sequence from at least two different start window sequences for transition from windowing with blocks of said first length to windowing with 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 a number of overlapped said second window functions;
• employing said selected start window sequence for a transition from windowing with blocks of said first length to windowing with blocks of said second length;
• and
• upon detecting signals varying weakly with time, selecting a stop window sequence from at least two different stop window sequences for transition from windowing with blocks of said second length to windowing with blocks of said first length, one of said stop window sequences including a first part having a number of overlapped said second window functions, 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;
• wherein, said length of said non-overlapping part and said number of 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.

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:

• windowing said time-discrete audio signals by employing said first window function producing blocks of said first length;
• and
• upon detecting signals varying strongly with time, employing a start window sequence for a transition from windowing with blocks of said first length to windowing with blocks of said second length;
• said start window sequence 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 a number of said second window functions being overlapped;
• wherein said length of said non-overlapping part and said number of 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 is equal to a number of frequency coefficients obtained by said frequency transform of time-discrete audio signals windowed by said first window function.

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:

• windowing said time-discrete audio signals by employing said second window function producing blocks of said second length;
• and
• upon detecting signals varying weakly with time, employing a stop window sequence for transition from windowing with blocks of said second length to windowing with blocks of said first length, said stop window sequence including a first part having a number of said second window functions being overlapped, 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;
• wherein, said length of said non-overlapping part and said number of 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 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.