For lack of any proved method of objective assessment the degree of non-linear distortion permissible in transmission systems which handle high quality speech and music programmes has been decided, up to the present, entirely on the basis of long experience. While collecting data to support a more factual approach to this subject the following experiments have been made. Pulses of pure tone, rather like staccato piano notes, have been distorted in various ways and the 'unpleasantness' of the resulting sounds have been compared, and an objective criterion, Ct, computed. This shows satisfactory correlation with the unpleasantness