Low bit rate voice coding method and device

Claim 2

A process for low-rate coding a base-band signal x(n) derived from a signal s(n) provided by a voice terminal and sampled at a first rate, said process including: a) splitting the base-band signal frequency bandwidth into at least two sub-band signals; b) sub-sampling each sub-band signal content to a lower rate than said first rate; c) selecting the sub-sampled sub-band contents best matching the voice terminal signal as being representative of said voice terminal derived signal to be further encoded at low rate.

Claim 3

A process according to claim 1 wherein said selecting includes: splitting each sub-sampled sub-band signal into fixed length blocks of samples; measuring the energy content of each fixed length block of samples within each sub-sampled sub-band signal; and selecting the highest energy sub-band sub-sampled signal to be further encoded at a low rate.

Claim 4

A process according to claim 1 wherein said selecting includes: up-sampling each sub-sampled sub-band signal back to said first rate; subtracting each up-sampled sub-band signal from the original base band signal to derive a sub-band error signal therefrom; and selecting the sub-band signal presenting the lowest error signal for being representative of said voice terminal derived signal to be low-rate encoded.

Claim 5

A low rate voice coding device of the type wherein a voice signal s(n) sampled at a first rate, is decorrelated through a short-term filter into a residual signal r(n) further processed to derive therefrom an error residual signal x(n), which x(n) is then block coded into lower sampled sequences of samples with a Regular Pulse Excited (RPE) coder, the improvement whereby said RPE coder includes: filtering means for filtering said x(n) signal into at least one low frequency band signal y1(n) and one high frequency band signal y2(n); down sampling means for sub-sampling y1(n) and y2(n) each into at least two sub-sampled sequences (x1(n); x2(n)) and (x3(n); x4(n)) respectively; up-sampling means for respectively up-sampling said sub-sampled sequences x1(n), x2(n), x3(n) and x4(n) into sequences x1'(n), x2'(n), x3'(n) and x4'(n) up-sampled back to said first rate; coding error means for computing coding error data dj(n)=x(n)-xj'(n) for j=1, . . . , 4 grid selection means for comparing said dj(n) to each other based on a mean squared criteria and deriving therefrom the xj(n) sequence representing the RPE encoded x(n).

Claim 6

A low rate voice coding device of the type wherein a voice signal s(n) sampled at a first rate, is decorrelated through a short-term filter into a residual signal r(n) further processed to derive therefrom an error residual signal x(n), which x(n) is then block coded into lower sampled sequences of samples with a Regular Pulse Excited (RPE) coder, the improvement whereby said RPE coder includes: filtering means for filtering said x(n) signal into at least one low frequency band signal y1(n) and one high frequency band signal y2(n); down sampling means for sub-sampling y1(n) and y2(n) each into at least two sub-sampled sequences (x1(n); x2(n)) and (x3(n); x4(n)) respectively; up-sampling means for respectively up-sampling said sub-sampled sequences x1(n), x2(n), x3(n) and x4(n) into sequences x1'(n), x2'(n), x3'(n) and x4'(n) up-sampled back to said first rate; coding error means for computing coding error data dj(n)=x(n)-xj'(n) for j=1, . . . , 4 grid selection means for comparing said dj(n) to each other based on a mean squared criteria and deriving therefrom the xj(n) sequence representing the RPE encoded x(n).

Claim 7

A low rate voice coding device according to claim 4 wherein said grid selection means include: inverse short-term filtering means; means for feeding each said dj(n) data into said inverse filtering means; summing means fed with said dj(n) and deriving error energy data Ej(n) therefrom whereby the RPE representative sequence would be selected for minimal Ej(n).