The ideal speech-processing system, taking its input from a noisy environment, would be able to select a target voice whilst attenuating competing voices and other background noises. In exploring possible noise-reduction strategies, we have evaluated two algorithms designed to separate the voices of talkers who are speaking simultaneously, with periodic excitation at similar overall intensities. Both approaches are pitch-based and exploit the regularity in the harmonic structure of voiced speech. The first involves attenuating the periodic excitation of the competing voice via a cepstrum. The second method is derived from the procedure for Harmonic Selection (ref 1). Perceptual evaluation of the two processing methods, in tests involving the separation of simultaneous vowels, monotone sentences and naturally-intoned sentences, has demonstrated a significant increase in performance for normal-hearing subjects. Improvements in performance in tests involving subjects with sensorineural hearing-impairments suggest possible applications in future digital signal-processing hearing-aids.