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Abstract

A digital data rate compression system accepts an input digital signal having a plurality of samples at a given rate and outputs a digital signal at one-half of the given rate, or as an expansion system outputs a digital signal at twice the given rate. The digital data rate reduction technique uses multi-rate digital filtering in the form of a half bandwidth filter. In the case of the digital filter the input digital signal is separated into even and odd samples which are input to separate delay lines at one-half the given rate. The even samples are summed in pairs symmetrically about the center of the even delay line, and each pair is weighted according to a modified sin(x)/x function with simple coefficients which may be accomplished by additions and shifts, to eliminate the need for multipliers. For data rate reduction the even sample pairs from the even delay line and the odd samples from the odd sample delay line are combined to form an average of the even samples and the odd samples which is the coded digital signal at one-half the given rate. For data rate expansion a multiplexer may be used to combine the even and odd samples to produce an output digital signal at twice the given rate to decode the coded digital signal.

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