Advanced quantizer

A transform-based audio decoder configured to decode a bitstream to provide a reconstructed audio signal;

• the decoder comprising hardware implementing
• a dither generator configured to select one of M pre-determined dither realizations, and configured to generate a plurality of dither values based on the selected dither realization;
• wherein M is an integer greater than one;
• wherein the plurality of dither values is used by an inverse quantization unit comprising a dithered quantizer configured to determine a corresponding plurality of quantized coefficients based on a corresponding plurality of quantization indices;
• and
• an entropy decoder configured to select a codebook from M pre-determined codebooks and configured to entropy decode coefficient data from the bitstream using the selected codebook, to provide the plurality of quantization indices;
• wherein the M pre-determined codebooks are associated with the M pre-determined dither realizations, respectively;
• wherein the M pre-determined codebooks have been trained using the M pre-determined dither realizations, respectively;
• and wherein the entropy decoder is configured to select the codebook associated with the dither realization selected by the dither generator;
• wherein the entropy decoder is configured to determine the reconstructed audio signal based on the plurality of quantized coefficients.

A method for encoding an audio signal into a bitstream;

• the method comprising
• determining a plurality of quantization indices by quantizing a plurality of coefficients from a block of coefficients using a dithered quantizer;
• wherein the plurality of coefficients is associated with a plurality of corresponding frequency bins;
• wherein the block of coefficients is derived from the audio signal;
• selecting one of M pre-determined dither realizations;
• generating a plurality of dither values for quantizing the plurality of coefficients, based on the selected dither realization;
• wherein M is an integer greater one;
• selecting a codebook from M pre-determined codebooks;
• entropy encoding the plurality of quantization indices using the selected codebook;
• wherein the M pre-determined codebooks are associated with the M pre-determined dither realizations, respectively;
• wherein the M pre-determined codebooks have been trained using the M pre-determined dither realizations, respectively;
• wherein the selected codebook is associated with the selected dither realization;
• and
• inserting coefficient data indicative of the entropy encoded quantization indices into the bitstream.

A method for decoding a bitstream to provide a reconstructed audio signal;

• the method comprising
• selecting one of M pre-determined dither realizations;
• generating a plurality of dither values based on the selected dither realization;
• wherein M is an integer greater one;
• wherein the plurality of dither values is used by an inverse quantization unit comprising a dithered quantizer to determine a corresponding plurality of quantized coefficients based on a corresponding plurality of quantization indices;
• selecting a codebook from M pre-determined codebooks;
• entropy decoding coefficient data from the bitstream using the selected codebook, to provide the plurality of quantization indices;
• wherein the M pre-determined codebooks are associated with the M pre-determined dither realizations, respectively;
• wherein the M pre-determined codebooks have been trained using the M pre-determined dither realizations, respectively;
• and wherein the selected codebook is associated with the selected dither realization;
• and
• determining the reconstructed audio signal based on the plurality of quantized coefficients.

A method for encoding a speech signal into a bitstream;

• the method comprising:
• receiving a plurality of sequential blocks of transform coefficients comprising a current block and one or more previous blocks;
• wherein the plurality of sequential blocks is indicative of samples of the speech signal;
• determining a current block of flattened transform coefficients by flattening the corresponding current block of transform coefficients using a corresponding current block envelope;
• determining a current block of estimated flattened transform coefficients based on one or more previous blocks of reconstructed transform coefficients and based on one or more predictor parameters;
• wherein the one or more previous blocks of reconstructed transform coefficients have been derived from the one or more previous blocks of transform coefficients;
• determining a current block of prediction error coefficients based on the current block of flattened transform coefficients and based on the current block of estimated flattened transform coefficients;
• and
• determining coefficient data for the bitstream based on quantization indices associated with the current block of prediction error coefficients;
• encoding the speech signal into the bitstream based on the coefficient data.

A method for decoding a bitstream to provide a reconstructed speech signal;

• the method comprising
• determining a current block of estimated flattened transform coefficients based on one or more previous blocks of reconstructed transform coefficients and based on one or more predictor parameters derived from the bitstream;
• determining a current block of quantized prediction error coefficients based on coefficient data comprised within the bitstream;
• determining a current block of reconstructed flattened transform coefficients based on the current block of estimated flattened transform coefficients and based on the current block of quantized prediction error coefficients;
• determining a current block of reconstructed transform coefficients by providing the current block of reconstructed flattened transform coefficients with a spectral shape, using a current block envelope;
• and
• determining the reconstructed speech signal based on the current block of reconstructed transform coefficients.