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US 4,538,234 AGranted
Adaptive predictive processing system
AssigneeNippon Telegraph & Telephone Public Corporation
InventorsMasaaki Honda, Fumitada Itakura, Nobuhiko Kitawaki
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Abstract
An adaptive predictive coding (APC) and adaptive kit allocation (ABA) system which splits a speech signal into a plurality of bands, subjecting each signal to adaptive predictive coding and adaptively changes quantization characteristics in the adaptive predictive coding so that quantization noise may become small. An average amplitude (not average power) of the signal of each band is detected for each temporal sub-interval, and a quantization bit number and a quantization step size are adaptively determined from the average amplitude for each sub-interval, thereby permitting reduction of the quantity of hardware used.
Claims15
An adaptive predictive processing system comprising:
- sub-band splitting means for splitting an input signal into a plurality of sub-bands and producing sampled sub-band signals from the respective sub-bands;
- adaptive predictive coding means connected to the respective outputs of said sub-band splitting means for subjecting the respective sub-band signals to adaptive predictive coding and producing adaptively quantized residual signals for the respective sub-bands, each of said adaptive predictive coding means including linear predictor means for producing a predicted value signal based on the quantized residual signal, a subtractor for receiving corresponding one of the subband signals from the input of said adaptive predictive means and the predicted value signal from said predictor means and providing therefrom a difference therebetween as a prediction residual signal, quantizer means connected to the output of said subtractor for producing the quantized residual signal, and adder means having inputs connected to the output sides of said quantizer means and said linear predictor means for adding the quantized residual signal and the predicted value signal to produce a locally decoded sub-band signal and supplying the locally decoded sub-band signal to the input of said linear predictor means;
- inverse filter means connected to the respective outputs of said sub-band splitting means for producing pseudo-residual signals of the respective sub-bands by subjecting the respective sub-band signals to inverse filtering processes;
- pitch detecting means connected to one of the outputs of said sub-band splitting means corresponding to the lowest subband, for detecting a pitch period T.sub.p of the sub-band signal;
- sub-interval setting means connected to the output of said pitch detecting means and one of the outputs of said inverse filter means corresponding to the lowest sub-band, for dividing a pitch interval in the pseudo-residual signal equal to the detected pitch period into a plurality of sub-intervals and setting a sub-interval position T.sub.d of the pitch interval relative to an analysis frame in the pseudo-residual signal;
- average amplitude detecting means connected to the respective outputs of said inverse filter means and the output of said sub-interval setting means, for detecting average amplitudes Uij of the pseudo-residual signals in the respective subbands during each of the sub-intervals;
- quantization bit number allocation means connected to the outputs of said average amplitude detecting means, for receiving the detected average amplitudes Uij of the respective pseudo-residual signals during each of the sub-intervals and computing, from the average amplitudes Uij, a number of bits Rij to be allocated to each of the sub-intervals in the respective sub-bands;
- and
- quantization step size computing means connected to the outputs of said quantization bit number allocation means and the output of said average amplitude detecting means, for receiving therefrom the computed allocation bit numbers Rij and the average amplitudes Uij and computing, from the allocation bit numbers and the average amplitudes, quantization step sizes .DELTA.ij for the respective sub-intervals in the respective sub-bands, wherein the allocation bit numbers Rij from said quantization bit number allocation means and the quantization step sizes .DELTA.ij from said quantization step size computing means are supplied to said quantizer means in said adaptive predictive coding means of the corresponding sub-band, thereby to adaptively control therewith the quantization of the prediction residual signals in the respective sub-bands.
6 more elements
An adaptive predictive processing system which decodes a speech signal based on a code series of received quantized residual signal, an average amplitude signal of a pseudo-residual signal for each sub-interval of each sub-band and sub-interval information including pitch information and sub-interval position information, comprising:
- quantization bit number allocating means for computing a quantization bit number of each sub-interval of each sub-band from the average amplitude signal;
- code separating means for separating the code series of the quantized residual signal for each sub-band based on the quantization bit number allocated to each sub-interval in each sub-band with said quantization bit number allocating means;
- quantization step size allocating means connected to the output side of said quantization bit number allocating means, for determining a quantization step size of each sub-interval of each sub-band based on the quantization bit number of each sub-band and the average amplitude signal;
- decoding means connected to the output side of said code separating means for decoding and regenerating from the separated codes of the residual signal for each sub-band, a decoded residual signal for each sub-band through using the quantization step sizes and the quantization bit numbers corresponding thereto;
- lattice type predictive filter means connected to the output side of said decoding means for predictively reconstructing respective sub-band signals of the sub-bands in accordance with the decoded residual signals;
- and
- combining means connected to said predictive filter means for composing a speech signal from the reconstructed sub-band signals.
4 more elements
An adaptive predictive processing system comprising:
- sub-band splitting means for splitting each input signal of a plurality of channels into a plurality of frequency sub-bands and producing sampled sub-band signals from the respective sub-bands in each channel;
- adaptive predictive coding means connected to the respective outputs of said sub-band splitting means, for subjecting the sub-band signals of each channel to adaptive predictive coding by use of a lattice type filter in a linear predictor provided in each of said adaptive predictive coding means;
- and
- quantization bit and step size adaptation means connected to the respective outputs of said sub-band splitting means, for generating pseudo-residual signals of the respective sub-bands for each channel by subjecting the respective sub-band signals to inverse filtering processes, for detecting the pitch periods of the input signals of the respective channels, for dividing each of the pseudo-residual signals in an interval of the corresponding pitch period into a plurality of sub-intervals, the pitch intervals having positions defined relative to an analysis frame, for detecting average amplitudes of the pseudo-residual signals, and for adaptively computing from the average amplitudes, for each sub-interval, a quantization step and a quantization bit number to be used for adaptive quantization in said adaptive predictive coding means.
1 more element
Dependencies are inferred from the claim text.