grt@twitch.UUCP ( G.R.Tomasevich) (02/27/86)
Sorry people, my memory was faulty. R. L. Wightman and D. M. Green, "The Perception of Pitch," American Scientist, pp. 208-215, March-April 1974 discuss, among other things, the insensitivity of perceived pitch to the relative phases of constituent frequencies in complex waveforms. In some cases the sound is identical, but one counterexample to my statement is interesting. The authors refer to other work in which (apparently) equal amplitudes of 1000, 1200, 1400, 1600, 1800, and 2000 Hz are combined in cosine phase and also with random phases, and similar experiments. The perceived pitches of such pairs were always identical, even though the waveforms were quite different, as shown in Figure 6. They comment that the two sounded different, "there were slight differences in the roughness of the sound depending on the phase. Those with less extreme peaks sounded smoother." I will have to try this on our computer to hear whether the differences are masked by mu-255 quantization noise. Concerning stereo, which Dick Pierce (teddy!rdp) mentioned, I don't think that the apparent source position would be affected if the two channels had identical responses, in the absense of IMD. But then, I am not sure one could have nonlinear phase response without IMD. Concerning the RIAA equalization, I will concede that point, that the pre-emphasis and de-emphasis ought to be complementary. I remember doing two circuits I saw and getting different results, though I found an old HP 2115A BASIC program for only one of them, from around 1969. Being a pack rat has some advantages. -- George Tomasevich, ihnp4!twitch!grt AT&T Bell Laboratories, Holmdel, NJ