Methods and apparatus for implementing embedded scalable encoding and decoding of companded and vector quantized audio data

A computer-implemented method for audio encoding comprising:

• receiving an input audio signal;
• performing a time-domain to discrete frequency domain transformation on the input audio signal, the time-domain to discrete frequency domain transformation creating a plurality of frequency domain coefficients;
• organizing the frequency domain coefficients by frequency subband;
• for each subband:
• scaling the frequency domain coefficients with a first scaling factor, wherein the first scaling factor comprises a first scaling factor base and a first scaling factor exponent and where at least some of the first scaling factors for certain subbands differ from first scaling factors for other subbands;
• companding the frequency domain coefficients, wherein the scaled and companded frequency domain coefficients comprise a subband coefficient vector;
• vector quantizing the subband coefficient vector;
• determining a maximum norm of the quantized subband coefficient vector;
• and
• encoding the first scaling factor exponent and the maximum norm of the quantized subband coefficient vector, the first scaling factor exponent and the maximum norm of the quantized subband coefficient vector comprising side information for the subband;
• bitplane encoding the subband coefficients comprising the subband coefficient vectors on a subband basis using a plurality of bitplane levels, the subband coefficients bitplane encoded in descending order of importance, derived from the first scaling factor and the maximum norm;
• and
• combining the subband side information and bitplane encoded subband coefficients into a scalable bitstream from which the audio signal can be recovered at a scalable rate.

An encoder comprising:

• a transform unit adapted to perform a time domain to discrete frequency domain transformation on an audio signal, generating a plurality of spectral coefficients for each of a plurality of subbands;
• a scaling unit adapted to scale the spectral coefficients with a first scaling factor, the first scaling factor comprising a first scaling factor base and a first scaling factor exponent, and where at least some of the first scaling factors for certain subbands differ from first scaling factors for other subbands;
• a companding unit adapted to compand the spectral coefficients;
• a quantizing unit adapted to vector quantize the spectral coefficients on a subband basis, the scaling, companding and quantizing units together generating modified spectral coefficients;
• a side information generating unit adapted to generate side information for each of the plurality of subbands;
• and
• a bitplane encoding unit adapted to bitplane encode the modified spectral coefficients on a subband basis using a plurality of bitplane levels, the modified spectral coefficients bitplane encoded in descending order of importance;
• the bitplane encoding unit further adapted to combine the side information with the bitplane encoded modified spectral coefficients to form a scalable bitstream from which the audio signal can be recovered at a scalable rate.

An electronic device comprising:

• a transform unit adapted to receive an input audio signal, to perform a time-domain to discrete frequency domain transformation, the time domain to discrete frequency domain transformation creating a plurality of frequency domain coefficients, and to organize the frequency domain coefficients by frequency subband;
• a scaling unit adapted to scale frequency domain coefficients associated with each subband with a first scaling factor, wherein the first scaling factor comprises a first scaling factor base and a first scaling factor exponent, and wherein at least some of the first scaling factors for certain subbands differ from first scaling factors for other subbands;
• a companding unit adapted to compand the scaled frequency domain coefficients associated with each subband, wherein the scaled and companded frequency domain coefficients comprise scaled, companded subband coefficient vectors;
• a quantizing unit adapted to vector quantize the scaled, companded subband coefficient vectors;
• a side information unit adapted to encode side information for each subband, the side information comprising the first scaling factor exponent associated with the scaling factor applied to the subband, and a maximum norm of the quantized subband coefficient vector associated with the subband;
• and
• a bitplane encoding unit adapted to bitplane encode using a plurality of bitplane levels the subband coefficients comprising the vector quantized, companded and scaled subband coefficient vectors, the bitplane encoding unit further adapted to generate a scalable bitstream by combining the bitplane encoded subband coefficients and the side information.

A tangible memory medium storing a computer program executable by a digital processing apparatus of an electronic device, wherein when the computer program is executed operations are performed, the operations comprising:

• receiving an input audio signal;
• performing a time-domain to discrete frequency domain transformation, the time domain to discrete frequency domain transformation creating a plurality of frequency domain coefficients;
• organizing the frequency domain coefficients by frequency subband;
• for each subband:
• scaling the frequency domain coefficients with a first scaling factor, wherein the first scaling factor comprises a first scaling factor base and a first scaling factor exponent and where at least some of the first scaling factors for certain subbands differ from first scaling factors for other subbands;
• companding the frequency domain coefficients, wherein the scaled and companded frequency domain coefficients comprise a subband coefficient vector;
• vector quantizing the subband coefficient vector;
• determining a maximum norm of the quantized subband coefficient vector;
• encoding the first scaling factor exponent and the maximum norm of the quantized subband coefficient vector, the first scaling factor exponent and the maximum norm of the quantized subband coefficient vector comprising subband side information for the subband;
• and
• bitplane encoding the subband coefficients using a plurality of bitplane levels, and combining the bitplane encoded subband coefficients with the subband side information to create an embedded scalable bitstream.

A decoder comprising:

• a side information unit adapted to recover subband side information from a scalable bitstream comprised of bitplane-encoded modified spectral coefficients and the subband side information, the bitplane-encoded modified spectral coefficients encoding an audio signal recoverable at a scalable bitrate, the modified spectral coefficients modified as a result of scaling, companding and vector quantizing operations performed by an encoder;
• a bitplane decoding unit adapted to receive both a selected decode bitrate, the decoded side information, and the scalable bitstream, to select sufficient bits encoding the modified spectral coefficients on a bitplane level basis from the scalable bitstream so that the audio signal may be reproduced at a fidelity level corresponding to the selected decode bitrate, and to use the side information to obtain the subband order of significance and to obtain the modified spectral coefficients and their significance;
• a decompanding unit adapted to decompand the modified spectral coefficients on a subband basis at the fidelity level corresponding to the selected decode bitrate using the bits selected by the bitplane decoding unit;
• a scaling unit adapted to scale the decompanded modified spectral coefficients on a subband basis at the fidelity level corresponding to the selected decode bitrate by scaling the spectral coefficients on each subband with a first scaling factor, the first scaling factor comprising a first scaling factor base and a first scaling factor exponent, and where at least some of the first scaling factors for certain subbands differ from first scaling factors for other subbands;
• and
• a transform unit adapted to perform a discrete frequency domain to time domain transform on the ordered, scaled and decompanded modified spectral coefficients to reproduce a version of the audio signal at the fidelity level corresponding to the selected decode bitrate.