Multi-pulse excited linear predictive speech coder

Claim 2

A multi-pulse excited linear predictive speech coder comprising: a. a multi-pulse excitation signal generator for generating a multi-pulse excitation signal and having a control input; b. a linear-predictive speech synthesizer, for synthesizing a signal from the multi-pulse excitation signal to produce synthetic speech samples; c. means for receiving a reference speech signal; d. a difference generator for comparing the reference speech samples with the synthetic speech samples and producing a difference signal; e. means for perceptually weighting the difference signal to produce a weighted error signal; and f. means for controlling the multi-phase excitation signal generator in response to the weighted error signal to minimize the weighted error signal; wherein the improvement comprises: g. means for determining a position of a k th pulse in a given interval of the multi-pulse excitation signal, where k is an integer, the k th pulse being one for which the difference signal is minimized, including: i. means for producing an average magnitude auxiliary function (M k (n)), which is a measure of the energy of the weighted error signal determined from the multi-pulse excitation signal after (k-1) pulses; ii. means for identifying a value n' k of n for which the auxiliary function (M k (n)) is maximized; iii. means for determining a reduced interval, shorter than the given interval, in a region surrounding n' k ; and iv. means for searching for the k th pulse weighting the reduced interval, whereby computational complexity is reduced.

Claim 5

A multi-pulse excited linear predictive speech coder comprising: a. a multi-pulse excitation signal generator producing a multi-pulse excitation signal and having a control input; b. means for receiving a reference speech signal; c. means for analyzing the reference speech signal to produce a residual signal, said analyzing means performing an analyzing operation which is the inverse of a linear-predictive synthesizing operation which produces synthetic speech samples from the multi-pulse excitation signal, whereby a speech synthesizer performing the synthesizing operation may be omitted from the coder; d. means for generating a distance function signal measuring a distance between the residual signal and the multi-pulse excitation signal; e. means for perceptually weighting the distance function signal to create a weighted error signal; f. means for controlling the multi-pulse excitation generator in response to the weighted error signal to reduce the weighted error signal; and g. means for determining a position of a k th pulse in a given interval of the multi-pulse excitation signal, where k is an integer, the k th pulse being one for which the distance function signal is minimized, including: i. means for producing an average magnitude auxiliary function (M k (n)), which is a measure of the energy of the weighted error signal determined from the multi-pulse excitation signal after (k-1) pulses; ii. means for identifying a value n' k of n for which the auxiliary function (M k (n)) is maximized; iii. means for determining a reduced interval, shorter than the given interval, in a region surrounding n' k ; and iv. means for searching for the k th pulse weighting the reduced interval, whereby computational complexity is reduced.

Claim 6

A multi-pulse excited linear predictive speech coder comprising: a. a multi-pulse excitation signal generator producing a multi-pulse excitation signal and having a control input; b. means for receiving a reference speech signal; c. means for analyzing the reference speech signal to produce a residual signal, said analyzing means performing an analyzing operation which is the inverse of a linear-predictive synthesizing operation which produces synthetic speech samples from the multi-pulse excitation signal, whereby a speech synthesizer performing the synthesizing operation may be omitted from the coder; d. means for generating a distance function signal measuring a distance between the residual signal and the multi-pulse excitation signal; e. means for perceptually weighting the distance function signal to create a weighted error signal; f. means for controlling the multi-pulse excitation generator in response to the weighted error signal to reduce the weighted error signal; and g. means for determining a position of a k th pulse in a given interval of the multi-pulse excitation signal, where k is an integer, the k th pulse being one for which the distance function signal is minimized, including: i. means for producing an average magnitude auxiliary function (M k (n)), which is a measure of the energy of the weighted error signal determined from the multi-pulse excitation signal after (k-1) pulses; ii. means for identifying a value n' k of n for which the auxiliary function (M k (n)) is maximized; iii. means for determining a reduced interval, shorter than the given interval, in a region surrounding n' k ; and iv. means for searching for the k th pulse weighting the reduced interval, whereby computational complexity is reduced.

Claim 7

The coder of claim 3 wherein: the distance function is: ##EQU6## the auxiliary function is: ##EQU7## the given interval is less than an interval over which the distance function is calculated.

Claim 8

The method of claim 4 wherein: (a) the distance function generating step comprises the step of calculating the distance function as: ##EQU8## (b) the auxiliary function determining step comprises the step of calculating the auxiliary function as: ##EQU9## (c) the position determining step comprises determining within the given interval which is less than an interval over which the distance function is calculated.

Claim 9

The coder of claim 4 comprising the step of predicting a pitch after generating the multipulse excitation signals before the distance function generating means.

Claim 10

The coder of claim 3 comprising a pitch predictor coupled between the multi-pulse excitation generator and the distance function generating means.