Frequency-domain audio coding supporting transform length switching

An audio encoder, comprising an electronic circuit, programmed computer or microprocessor configured to:

• subject time-domain portions of an audio signal to transformation to obtain, for each time-domain portion, frequency-domain coefficients;
• inversely scale the frequency-domain coefficients according to scale factors,
• wherein the audio encoder configured to switch, for a predetermined frame, between
• performing one transform of a first transform length, and
• performing more than one transform of a second transform length, shorter than the first transform length;
• signal the switching for the predetermined frame by a signalization within the data stream for the predetermined frame,
• wherein the audio encoder is configured to:
• arrange, for the predetermined frame, the frequency-domain coefficients, inversely scaled according to scale factors, at a sequential order so as to obtain a sequence of frequency-domain coefficients by, depending on the signalization,
• sequentially arranging the frequency-domain coefficients of the one transform in case of one transform performed for the respective frame, and
• by interleaving the frequency-domain coefficients of the more than one transform of the respective frame in case of more than one transform performed for the respective frame, so that spectrally corresponding frequency-domain coefficients of the more than two transforms immediately follow each other;
• and
• wherein the frequency-domain coefficients are grouped into a number of scale factor bands which is independent from the signalization, and a scale factor is inserted into the data stream for each scale factor band.

A method for audio decoding, comprising:

• extracting a sequence of frequency-domain coefficients relating to a frame of an audio signal from a data stream;
• extracting scale factors for the frame from the data stream;
• subjecting the frequency-domain coefficients, scaled according to scale factors, to inverse transformation to obtain a time-domain portion of the audio signal;
• and
• subjecting the time-domain portion to an overlap-add process to obtain the audio signal,
• wherein the subjection to inverse transformation is responsive to a signalization within the data stream for the frame so as to, depending on the signalization, comprise:
• forming one transform out of the sequence of frequency-domain coefficients by maintaining a sequential order of the frequency-domain coefficients in the sequence of frequency-domain coefficients and subjecting the one transform, scaled according to the scale factors, to an inverse transformation of a first transform length, or
• forming more than one transform by de-interleaving the frequency-domain coefficients from the sequence of frequency-domain coefficients and subjecting, scaled according to the scale factors, each of the more than one transforms to an inverse transformation of a second transform length, shorter than the first transform length,
• wherein the frequency-domain coefficients are grouped into a number of scale factor bands which is independent from the signalization, and a scale factor is extracted from the data stream for each scale factor band.

A method for audio encoding, comprising:

• subjecting time-domain portions of an audio signal to transformation to obtain, for each time-domain portion, frequency-domain coefficients;
• inversely scaling the frequency-domain coefficients according to scale factors;
• switching for a predetermined frame between:
• performing one transform of a first transform length, and
• performing more than one transform of a second transform length, shorter than the first transform length;
• signaling the switching by a signalization for the predetermined frame within the data stream;
• arranging, for the predetermined frame, the frequency-domain coefficients, inversely scaled according to scale factors, at a sequential order so as to obtain a sequence of frequency-domain coefficients by, depending on the signalization,
• sequentially arranging the frequency-domain coefficients of the one transform in case of one transform performed for the respective frame, and
• by interleaving the frequency-domain coefficients of the more than one transform of the respective frame in case of more than one transform performed for the respective frame, so that spectrally corresponding frequency-domain coefficients of the more than two transforms immediately follow each other;
• and
• wherein the frequency-domain coefficients are grouped into a number of scale factor bands which is independent from the signalization, and a scale factor is inserted into the data stream for each scale factor band.