Audio encoder with adaptive short window grouping

An apparatus for encoding a data stream to generate an encoded output bitstream, the apparatus comprising:

• a quantization and coding module;
• an adaptive grouping perceptual model including,
• a perceptual entropy detector for determining a perceptual entropy level of a block from the data stream,
• a window length selector for selecting a long window if the perceptual entropy level is above a predetermined threshold and for otherwise selecting a plurality of short windows,
• a short window grouper, responsive to the window length selector having selected the plurality of short windows, to group the short windows in a number of groups that is greater than one and less than the number of short windows;
• and
• a bitstream encoder responsive to the adaptive grouping perceptual model and the quantization and coding module to generate the encoded output bitstream and include in it a parameter identifying grouping of the short windows.

An audio encoder comprising:

• a filterbank analyzer for receiving and performing time-to-frequency domain mapping upon audio input data;
• a quantization and coding module coupled to the filterbank analyzer for quantizing and encoding spectral data from the audio input data;
• an adaptive grouping psychoacoustic perceptual model for determining whether a block of the audio input data should be encoded as a long window or as a plurality of short windows, and for grouping the short windows according to respective perceptual entropy levels of each short window and its preceding short window;
• a bitstream encoder coupled to the quantization and coding module and to the adaptive grouping psychoacoustic perceptual model for generating an encoded audio output bitstream and including in the encoded audio output bitstream a parameter indicating how the short windows are grouped.

An MPEG AAC compatible audio encoder comprising:

• an adaptive grouping psychoacoustic perceptual model for receiving audio input data and for grouping short windows in N groups where N>1 and N<8;
• an iterative rate control loop responsive to the adaptive grouping psychoacoustic perceptual model;
• a scale factor extraction module responsive to the iterative rate control loop;
• a quantizer responsive to the scale factor extraction module;
• an entropy coding module responsive to the scale factor extraction module and the quantizer;
• and coupled to the iterative rate control loop;
• a previous-block analysis module responsive to the quantizer module;
• a modified discrete cosine transform module responsive to the adaptive grouping psychoacoustic perceptual model;
• a prediction module responsive to the previous-block analysis module and providing input to the scale factor extraction module;
• and
• a side information coding and bitstream formatting module responsive to the prediction module, the previous-block analysis module, and the entropy coding module, for generating an MPEG AAC compatible encoded audio output bitstream.

An article of manufacture bearing software for generating an encoded bitstream representing audio input data, wherein the software comprises:

• routines comprising a filterbank analyzer adapted to receive the audio input data and provide filterbank output;
• routines comprising an adaptive grouping psychoacoustic perceptual model adapted to determine perceptual entropy values of the audio input data and, responsive to the perceptual entropy values, to indicate one of a long window and a plurality of short windows, and, if the plurality of short windows are indicated, to generate a grouping parameter having a value indicating how the plurality of short windows are to be grouped, wherein the value of the grouping parameter indicates at least two groups and at least one of the groups includes at least two short windows;
• routines comprising a quantization and coding module adapted to quantize and code the filterbank output as long windows and short windows and to group the short windows in response to the grouping parameter;
• and
• routines comprising a bitstream encoder adapted to generate the encoded bitstream in response to output from the quantization and encoding module.