Bell Telephone Laboratories

Ronald Eldon Crochiere

Lawrence Richard Rabiner

Richard Robert Shively

James L Flanagan

Susan Anne Webber

A digital speech communication arrangement includes apparatus for partitioning a speech signal into a plurality of nonuniformly related, preassigned intelligibility contributing subbands, and quantized with an accuracy (bit allocation) based upon perceptual criteria. As a result, the quality of the coded signal is improved over that obtained from a single full-band coding of the total spectrum. 'Integer-band' sampling may be employed to alias the signal in an advantageous way before coding. Each subband portion is digitally encoded after sampling at a rate related to the bandwidth of the subband. The digital codes of the subband are combined and applied to a common communication channel. A replica of each subband is formed by separating the digital codes, producing a sampled form of each digital coded signal and selecting the subband of the speech signal from said sampled form. The subbands are combined to reconstruct the speech signal. Other features include: aliasing for efficient frequency transposition.

Digital speech communication system for minimizing quantizing noise

A general purpose interpolator-decimator circuit for increasing or decreasing the sampling rate of a digital signal by a factor L/M, where L and M are integers, is disclosed. The circuit includes means for determining each output sample by multiplying a sequence of previous input samples by a set of coefficients and accumulating the resulting products. L sets of coefficients, in which each coefficient is a function of the factors L and M, are stored in a specific sequence which permits sequential addressing of both the coefficients and input signal samples. A multistage decimator cascaded with a multistage interpolator to effect a narrow-band FIR filter is also disclosed.

Interpolation-decimation circuit for increasing or decreasing digital

In many digital processing systems it is necessary to delay an applied signal by a time interval which is not an integer multiple of the system sampling period. Disclosed herein is a digital phase shifter which utilizes a particular digital filtering scheme for supplying virtually any predetermined delay. Although conceptually related to the digital concepts of phase shift by interpolation and decimation in which the sampling rate is first increased and then restored to the original sampling rate after effecting the desired phase shift, the disclosed phase shifter operates entirely at the system sampling rate. This is accomplished by establishing a specific predetermined subset of digital filter coefficients and combining the coefficients with the input signal samples in a multiplier and accumulator circuit.

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Chatham, NJ, United States of America

Ronald Eldon Crochiere