Speech encoder

• US 5,448,683 A
• Filed: 08/30/1993
• Issued: 09/05/1995
• Est. Priority Date: 06/24/1991
• Status: Expired due to Fees

• Current Assignee: Kokusai Electric Co., Ltd.
• Original Assignee: Kokusai Electric Co., Ltd.
• Inventors: Naitoh, Masashi
• Primary Examiner(s): MacDonald, Allen R.
• Assistant Examiner(s): Doerrler, Michelle
• Application Number:
  US08/114,109
• Time in Patent Office: 736 Days
• Field of Search: 381/29-51, 395/2.12-2.13, 395/2.2-2.29, 395/2.35-2.37
• US Class Current: 704/203
• CPC Class Codes: G10L 19/06 Determination or coding of the spectral characteristics, e.g. of the short-term prediction coefficients
• CPC Class Codes: G10L 19/18 Vocoders using multiple modes
• CPC Class Codes: G10L 25/27 characterised by the analysis technique
• CPC Class Codes: H03H 21/0012 Digital adaptive filters

Abstract

A speech encoder circuit of a waveform coding system. An analog speech input signal having coded data therein is received by a buffer and split into two branches. In a first branch the input signal is applied to a subtractor of an adaptive predictor to obtain a predicted residual signal subjected to an orthogonal transformation in a discrete cosine transform unit to convert the residual signal into a frequency domain of each of the frames of the individual blocks. An adaptive encoder in the first branch quantizes the frequency domain frame and branches its digital coded output to a branch for output to a transmission line and to a decoding branch. In the second branch of the split input signal a first sample delay element delays the split input signal for a given number of samples and a first attenuator in the second branch delays the output of the first sample delay element a given amount of each frame received for application to the subtractor for obtaining the predicted residual signal. The coded signal in the decoding branch is applied to an adaptive decoder whose decoded output is subjected to an inverse orthogonal transformation by an inverse discrete cosine transform unit to obtain a signal applied to an input of an adder and delayed by a second delay element and attenuated by a second attenuator in the decoding branch with which processing of one frame ends. The outputs of the attenuators are applied to the subtractor for development of the predicted residual signal.

Claims

1. A speech encoder circuit for an adaptive transform coding system comprising:

a buffer for receiving and sampling an analog speech input signal into samples having frames and for splitting the speech input signal into two branches;

a substractor connected in a first branch of the two branches for receiving as one input individual one of said frames of the divided analog speech input signal to obtain therefrom a predicted residual signal;

a discrete cosine transform unit in said first branch connected to receive said residual signal from the subtractor and perform an orthogonal transform thereon to transform the residual signal into a frequency domain for each of said frames to obtain a transformation coefficient;

an adaptive encoder in said first branch receptive of the transformation coefficient as an output of the discrete cosine transform unit to quantize and encode the output of the frequency domain for each of said frames and for branching its coded output into branches for application to a transmission line and to a decoding branch;

a first sample delay element in a second branch of said two branch receptive of the split analog speech input signal from said buffer as current one of said frames of the analog speech input signal and delaying the split analog speech input signal received for a given number of samples for each of said frames;

a first attenuator receptive of the delayed analog speech input signal from said first sample delay element and attenuating by a given amount each of said frames of the received delayed analog speech input signal to obtain a first attenuated signal;

an adaptive decoder connected in the decoding branch for decoding a just preceding one of said frames of the branched coded output of said adaptive encoder to obtain a decoded digital output;

an inverse discrete cosine transform unit in the decoding branch receptive of the decoded digital output from the adaptive decoder and subjecting it to an inverse orthogonal transformation;

an adder in the decoding branch connected to the inverse discrete cosine transform unit to receive as one input an output of said inverse discrete cosine transform unit;

a second delay element in the decoding branch connected to receive an output of the adder for delaying the output of said adder by the number of delay samples corresponding to said just preceding one of said frames;

a second attenuator connected in the decoding branch for attenuating the output of said second delay element by an amount corresponding to said just preceding one of said frames to obtain a second attenuating signal and outputting the second attenuating signal as another input to said adder; and

a switch having contacts for supplying the first attenuated signal as another input of said subtractor, said contacts operable for supplying therethrough the output of said second attenuator as said another input to said subtractor in place of the output of said first attenuator only when a sample point, which precedes, by the number of delay samples of sample points in the frame to be processed by said subtractor is within the just preceding frame.

2. A speech encoder circuit for an adaptive transform coding system according to claim 1, in which said switch comprises a pair of fixed contacts connected to receive respectively outputs of said first attenuator and said second attenuator, and a movable contact operable to selectively connect alternatively said fixed contacts to said subtractor for inputting outputs of the first attenuator and of said second attenuator to said subtractor.