Encoding of periodic speech using prototype waveforms

A method for coding a quasi-periodic speech signal, wherein the speech signal is represented by a residual signal generated by filtering the speech signal with a Linear Predictive Coding (LPC) analysis filter, and wherein the residual signal is divided into frames of data, comprising the steps of:

• extracting a current prototype from a current frame of the residual signal;
• calculating a first set of parameters which describe how to modify a previous prototype such that said modified previous prototype approximates said current prototype;
• selecting one or more codevectors from a first codebook, wherein said codevectors when summed approximate the difference between said current prototype and said modified previous prototype, and wherein said codevectors are described by a second set of parameters;
• reconstructing a current prototype based on said first and second set of parameters;
• interpolating the residual signal over the region between said current reconstructed prototype and a previous reconstructed prototype;
• and
• synthesizing an output speech signal based on said interpolated residual signal,
• wherein said step of calculating a first set of parameters comprises the steps of:
• (i) circularly filtering said current prototype, forming a target signal;
• (ii) extracting said previous prototype;
• (iii) warping said previous prototype such that the length of said previous prototype is equal to the length of said current prototype;
• (iv) circularly filtering said warped previous prototype;
• and
• (v) calculating an optimum rotation and a first optimum gain, wherein said filtered warped previous prototype rotated by said optimum rotation and scaled by said first optimum gain best approximates said target signal.

A method for coding and decoding a quasi-periodic speech signal that is transmitted from a transmission source to a receiver, wherein the speech signal is represented by a residual signal generated by filtering the speech signal with a Linear Predictive Coding (LPC) analysis filter, and wherein the residual signal is divided into frames of data, comprising the steps of:

• extracting a current prototype from a current frame of the residual signal;
• calculating a first set of parameters which describe how to modify a previous prototype such that said modified previous prototype approximates said current prototype;
• selecting one or more codevectors from a first codebook, wherein said codevectors when summed approximate the difference between said current prototype and said modified previous prototype, and wherein said codevectors are described by a second set of parameters;
• transmitting said first set of parameters and said second set of parameters to the receiver;
• forming a reconstructed current prototype based on said first set of parameters, said second set of parameters and a reconstructed previous prototype;
• filtering said reconstructed current prototype with an LPC synthesis filter;
• filtering said previous reconstructed prototype with said LPC synthesis filter;
• interpolating over the region between said filtered reconstructed current prototype and said filtered reconstructed previous prototype, thereby forming an output speech signal.

A system for coding and decoding a quasi-periodic speech signal that is transmitted from a transmission source to a receiver, wherein the speech signal is represented by a residual signal generated by filtering the speech signal with a Linear Predictive Coding (LPC) analysis filter, and wherein the residual signal is divided into frames of data, comprising:

• means for extracting a current prototype from a current frame of the residual signal;
• means for calculating a first set of parameters which describe how to modify a previous prototype such that said modified previous prototype approximates said current prototype;
• means for selecting one or more codevectors from a first codebook, wherein said codevectors when summed approximate the difference between said current prototype and said modified previous prototype, and wherein said codevectors are described by a second set of parameters;
• means for transmitting said first set of parameters and said second set of parameters to the receiver;
• means for forming a reconstructed current prototype based on said first set of parameters, said second set of parameters, and a reconstructed previous prototype;
• means for interpolating over the region between said reconstructed current prototype and said reconstructed previous prototype to form an interpolated residual signal;
• and
• means for synthesizing an output speech signal based on said interpolated residual signal.

A system for coding a quasi-periodic speech signal, wherein the speech signal is represented by a residual signal generated by filtering the speech signal with a Linear Predictive Coding (LPC) analysis filter, and wherein the residual signal is divided into frames of data, comprising:

• means for extracting a current prototype from a current frame of the residual signal;
• means for calculating a first set of parameters which describe how to modify a previous prototype such that said modified previous prototype approximates said current prototype;
• means for selecting one or more codevectors from a first codebook, wherein said codevectors when summed approximate the difference between said current prototype and said modified previous prototype, and wherein said codevectors are described by a second set of parameters;
• means for reconstructing a current reconstructed prototype based on said first and second set of parameters;
• means for interpolating the residual signal over the region between said current reconstructed prototype and a previous reconstructed prototype;
• means for synthesizing an output speech signal based on said interpolated residual signal,
• wherein said means for calculating a first set of parameters comprises:
• a first circular LPC synthesis filter, coupled to receive said current prototype and to output a target signal;
• means for extracting said previous prototype from a previous frame;
• a warping filter, coupled to receive said previous prototype, wherein said warping filter outputs a warped previous prototype having a length equal to the length of said current prototype;
• a second circular LPC synthesis filter, coupled to receive said warped previous prototype, wherein said second circular LPC synthesis filter outputs a filtered warped previous prototype;
• and
• means for calculating an optimum rotation and a first optimum gain, wherein said filtered warped previous prototype rotated by said optimum rotation and scaled by said first optimum gain best approximates said target signal.

A system for coding and decoding a quasi-periodic speech signal that is transmitted from a transmission source to a receiver, wherein the speech signal is represented by a residual signal generated by filtering the speech signal with a Linear Predictive Coding (LPC) analysis filter, and wherein the residual signal is divided into frames of data, comprising:

• means for extracting a current prototype from a current frame of the residual signal;
• means for calculating a first set of parameters which describe how to modify a previous prototype such that said modified previous prototype approximates said current prototype;
• means for selecting one or more codevectors from a first codebook, wherein said codevectors when summed approximate the difference between said current prototype and said modified previous prototype, and wherein said codevectors are described by a second set of parameters;
• means for transmitting said first set of parameters and said second set of parameters to the receiver;
• means for forming a reconstructed current prototype based on said first set of parameters, said second set of parameters, and a reconstructed previous prototype;
• a first LPC synthesis filter, coupled to receive said reconstructed current prototype, wherein said first LPC synthesis filter outputs a filtered reconstructed current prototype;
• a second LPC synthesis filter, coupled to receive a reconstructed previous prototype, wherein said second LPC synthesis filter outputs a filtered reconstructed previous prototype;
• and
• means for interpolating over the region between said filtered reconstructed current prototype and said filtered reconstructed previous prototype, thereby forming an output speech signal.

A method for reducing the transmission bit rate of a speech signal, comprising:

• extracting a current prototype waveform from a current frame of the speech signal;
• comparing the current prototype waveform to a past prototype waveform from a past frame of the speech signal, wherein a set of rotational parameters is determined that modifies the past prototype waveform to approximate the current prototype waveform and a set of difference parameters is determined that describes the difference between the modified past prototype waveform and the current prototype waveform;
• transmitting the set of rotational parameters and the set of difference parameters instead of the current prototype waveform to a receiver;
• and
• reconstructing the current prototype waveform from the received set of rotational parameters, the set of difference parameters, and a previously reconstructed past prototype waveform.

An apparatus for coding a quasi-periodic speech signal, wherein the speech signal is represented by a residual signal generated by filtering the speech signal with a Linear Predictive Coding (LPC) analysis filter, and wherein the residual signal is divided into frames of data, compring:

• an extraction module for extracting a current prototype from a current frame of the residual signal and a previous protype from a previous frame;
• a first circular LPC synthesis filter, coupled to receive said current prototype and to output a target signal;
• a warping filter, coupled to receive said previous protoype, wherein said warping filter outputs a warped previous prototype having a length equal to the length of said current prototype;
• a second circular LPC synthesis filter, coupled to receive said warped previous prototype, wherein said second circular LPC synthesis filter outputs a filtered warped previous prototype;
• and
• a rotational correlator for calculating an optimum rotation and a first optimum gain, wherein said filtered warped previous prototype rotated by said optimum rotation and scaled by said first optimum gain best approximates said target signal;
• and a multi-stage codebook for generating one or more codevectors, wherein said codevectors when summed approximate the difference between said current prototype and said modified previous prototype, and wherein said codevectors are described by a second set of parameters.