Abstract: A method and apparatus for detecting multifrequency tones in a received signal by summing aperiodic samples and without using bandpass filters. In a receiver capable of detecting m different tones each comprised of n different frequencies, the apparatus performs m parallel summations each of 2.sup.n samples of the received signal. Each summation corresponds to a different detectable tone. In each summation, an initial sample is followed by samples delayed from it by respective half-periods of the frequencies comprising the corresponding tone and by samples delayed from the initial sample by combinations of different ones of such half-periods. The detection of a particular tone is indicated when the corresponding sum is zero and all other sums have finite values.

Abstract: A shift-companded, or n:m, pulse code, representing on a time-amplitude basis the information of a conventional, amplitude companded, pulse code, is converted to a linear, digital, amplitude, pulse code by first converting the shift-companded amplitude information into 2s-complement form with a number of bits sufficient to yield substantially the same resolution of the encoded information as did the shift-companded code form. Thereafter half of the 2s-complement code words are loaded into an accumulator to be averaged. The resulting digital word representing the average is in 2s-complement, linear PCM format and is thus readily useful for data processing or for further conversion to a commercial, companded, transmission code.