Multi-rate frequency domain interpolative speech CODEC system

A coding system for a codec, comprising:

• A linear prediction front end adapted to process an input signal to provide LP parameters which are quantized and encoded over predetermined intervals and are used to compute a LP residual signal;
• an open loop pitch estimator adapted to process the LP residual signal, pitch information, pitch interpolation information and provide a pitch contour within the predetermined intervals;
• a prototype waveform extraction module, which is adapted in response to the LP residual signal and the pitch contour to extract a prototype waveform (PW) for a number of equal subintervals within the predetermined intervals and to extract an additional approximate PW in the subinterval immediately after the ending of a previous subinterval;
• a PW gain computation module, adapted to compute a PW gain for substantially all the subintervals;
• and
• a gain vector predictive vector quantization (VQ) module, adapted to quantize and encode the PW gains for substantially all the subintervals after they are filtered by a weighted window, decimated, and after subtracting from them a predicted average PW gain value for a current predetermined interval computed from the quantized PW gain values of a preceding predetermined interval.

A frequency domain interpolative (FDI) coder/decoder (codec), comprising:

• a PW magnitude quantizer, adapted to perform the following:
• directly quantize a prototype waveform (PW) in a magnitude domain for substantially every frame without said PW being decomposed into complex components;
• hierarchically quantize a PW magnitude vector based on a voicing classification using a mean-deviations representation;
• adaptively vector quantize the mean component of the representation in multiple subbands;
• derive a variable dimension deviations vector as the difference of the input PW magnitude vector and the full band representation of the quantized PW subband mean vector for all harmonics;
• select a fixed dimensional deviations subvector from the said variable dimensional deviations vector based on location of speech formant frequencies for a subframe;
• and
• provide the said fixed dimensional deviations subvector for adaptive vector quantization.

A coding system for a coder/decoder (codec), comprising:

• a linear prediction (LP) front end, adapted to process an input signal which provides LP parameters that are computed during a predetermined interval;
• an open loop pitch estimator, adapted to perform pitch estimation on said input signal for substantially all of said predetermined intervals;
• a voice activity detection module, that uses the LP parameters and pitch information;
• a voicing measure computation module, adapted to provide a voicing measure that characterizes a degree of voicing and is derived from a plurality of input parameters that are correlated to the degree of periodicity of the input signal for substantially all predetermined intervals;
• a prototype waveform (PW) subband correlation computation module, adapted to provide a PW subband correlation vector, said PW subband correlation vector characterizing a degree of correlation between successive PW vectors as a function of frequency and computed for substantially all predetermined intervals;
• an adaptive bandwidth broadening module, adapted to reduce annoying artifacts due to spurious spectral peaks by performing the following:
• compute a measure of VAD likelihood based on voice activity detection (VAD) flags for a preceding, a current and a next predetermined interval;
• and
• compute average PW gain values for inactive predetermined intervals and active unvoiced predetermined intervals.

A low bit rate coding system for a coder/decoder (codec), comprising:

• a linear prediction (LP) front end, adapted to process an input signal which provides LP parameters that are computed during a predetermined interval;
• an open loop pitch estimator, adapted to perform pitch estimation on said input signal for substantially all of said predetermined intervals;
• a voice activity detection module, adapted to process and provide the LP parameters and pitch information to the decoder;
• a prototype waveform (PW) encoder, adapted to provide a look ahead based on said predetermined interval in order to smooth PW parameters;
• and
• a voicing measure computation module, adapted to provide a voicing measure, said voicing measure characterizing a degree of voicing derived from a plurality of input parameters that are correlated to the degree of periodicity of the input signal for substantially all predetermined intervals.

A low bit rate coding system for a coder/decoder (codec), comprising:

• a linear prediction (LP) front end, adapted to process an input signal which provides LP parameters that are estimated, quantized and transmitted for substantially all frames of a first duration;
• an open loop pitch estimator, adapted to perform pitch estimation on said input signal for substantially all of said frames of a first duration and quantize and transmit pitch information for substantially all frames of a second duration;
• a voice activity detection module, adapted to combine voice activity detection (VAD) flags associated with two successive frames of a first duration based on processing the LP parameters and the pitch information every frame of a first duration and transmitting the VAD flags to the decoder substantially every frame of a second duration;
• and
• a prototype waveform (PW) encoder, adapted to provide a look ahead frame based on said frame of a first duration in order to smooth PW parameters including at least one of PW gain, a voicing measure, subband correlations and spectral magnitude.

A method for providing adaptive bandwidth broadening to an encoder of a coder/decoder (codec), comprising:

• processing an input signal which provides LP parameters that are computed during a predetermined interval;
• performing pitch frequency estimation on said input signal for substantially all of said predetermined intervals;
• deriving a spectrum sampling frequency for said predetermined interval as the pitch frequency or its integer submultiple depending on the pitch frequency;
• determining a LP power spectrum at the harmonics of said spectrum sampling frequency for said input signal for said frame;
• computing a peak to average ratio of said LP spectrum based on said spectrum sampling frequency of said frame;
• and
• adaptively bandwidth broadening said LP filter coefficients based on said peak to average ratio of said LP spectrum for all harmonic multiples of said spectral sampling frequency.

A method of providing a coding system for a codec, comprising:

• processing an input signal to provide LP parameters which are quantized and encoded over predetermined intervals and are used to compute a LP residual signal;
• processing the LP residual signal, pitch information, pitch interpolation information and providing a pitch contour within the predetermined intervals;
• extracting a prototype waveform (PW) for a number of equal subintervals within the predetermined intervals and extracting an additional approximate PW in the subinterval immediately after the ending of a previous subinterval in response to the LP residual signal and the pitch contour;
• computing a PW gain for substantially all the subintervals;
• and
• quantizing and encoding the PW gains for substantially all the subintervals after the subintervals are filtered by a weighted window, decimated, and subtracted from a predicted average PW gain value for a current predetermined interval which is computed from the quantized PW gain values of a preceding predetermined interval.

A method of providing a coding system for a frequency domain interpolative (FDI) coder/decoder (codec), comprising:

• directly quantizing a prototype waveform (PW) in a magnitude domain for substantially every frame without said PW being decomposed into complex components;
• hierarchically quantizing a PW magnitude vector based on a voicing classification using a mean-deviations representation;
• adaptively vector quantizing the mean component of the representation in multiple subbands;
• deriving a variable dimension deviations vector as the difference of the input PW magnitude vector and the full band representation of the quantized PW subband mean vector for all harmonics;
• selecting a fixed dimensional deviations subvector from the said variable dimensional deviations vector based on a location of speech formant frequencies for a subframe;
• and
• providing the said fixed dimensional deviations subvector for adaptive vector quantization.

A method of providing a coding system for a coder/decoder (codec), comprising:

• processing an input signal which provides LP parameters that are computed during a predetermined interval;
• performing a pitch estimation on said input signal for substantially all of said predetermined intervals;
• processing the LP parameters and pitch information;
• providing a voicing measure that characterizes a degree of voicing and is derived from a plurality of input parameters that are correlated to the degree of periodicity of the input signal for substantially all predetermined intervals;
• providing a PW subband correlation vector, said PW subband correlation vector characterizing a degree of correlation between successive PW vectors as a function of frequency and computed for substantially all predetermined intervals;
• reducing annoying artifacts due to spurious spectral peaks by performing the following:
• computing a measure of VAD likelihood based on voice activity detection (VAD) flags for a preceding, a current and a next predetermined interval;
• and
• computing average PW gain values for inactive predetermined intervals and active unvoiced predetermined intervals.

A method of providing a low bit rate coding system for a coder/decoder (codec), comprising:

• processing an input signal which provides LP parameters that are computed during a predetermined interval;
• performing pitch estimation on said input signal for substantially all of said predetermined intervals;
• processing the LP parameters and pitch information to the decoder;
• providing a look ahead based on said predetermined interval in order to smooth PW parameters;
• and
• providing a voicing measure, said voicing measure characterizing a degree of voicing derived from a plurality of input parameters that are correlated to the degree of periodicity of the input signal for substantially all predetermined intervals.

A method of providing a low bit rate coding system for a coder/decoder (codec), comprising:

• processing an input signal which provides LP parameters that are estimated, quantized and transmitted for substantially all frames of a first duration;
• performing a pitch estimation on said input signal for substantially all of said frames of a first duration and quantizing and transmiting pitch information for substantially all frames of a second duration;
• combining voice activity detection (VAD) flags associated with two successive frames of a first duration;
• processing the LP parameters and the pitch information every frame of a first duration and transmitting the VAD flags to the decoder substantially every frame of a second duration;
• and
• providing a look ahead frame based on said frame of a first duration in order to smooth PW parameters including at least one of PW gain, a voicing measure, subband correlations and a spectral magnitude.