A subjective evaluation of the effects of smoothing and quantization of the parameters for formant‐coded voiced speech has been carried out. Thresholds were obtained for the degree of smoothing or quantization of specified parameters associated with a just noticeable degradation of all‐voiced sentence material. Average quantization threshold levels obtained were: pitch period, 3.9 bits; first formant, 2.7 bits; second formant, 3.1 bits. The average of low‐pass filter bandwidth thresholds for the simultaneous smoothing of formants was 7.6 Hz per formant; for pitch‐period data the low‐pass filter bandwidth threshold was 3.9 Hz. With simultaneous low‐pass filtering and quantization, the estimated over‐all bit rate for the coded parameters of all‐voiced speech was approximately 200 bits/sec.