source file: m1400.txt Date: Wed, 29 Apr 1998 21:12:27 -0500 (CDT) Subject: Orchestral-Instrument Aperiodicty Yet Again From: mr88cet@texas.net (Gary Morrison) I looked over a variety of sounds in the sound library I used for testing the sound analysis program I worked on for a few years several years ago. I'm now willing to accept that this effect of little peaks and troughs in a sound bobbing up and down in a tone is not nearly as common as I recalled it to have been. In fact when I picked out that example tone to post as that GIF file, I'm amazed that I chanced upon a sound file that shows that effect on just my second try. Just now I looked at 20 or so fundamental-mode waves, and only noticed 2 that showed apparently systematic aperiodicities. There were plenty of random fluctuations though, not surprisingly. So until I now in this discussion, I was willing to accept Paul E's theoretical model predicting exact periodicity was probably a good model, but not a completely infallible one. I assumed from having seen systematic aperiodicities that it was valid for the basic variables, but that there apparently was some smaller consideration that it didn't take into account. But looking over quite a few applicable waveforms just now, has increased up my confidence in Paul's model by a factor of 10 or so. Systematic aperiodicities of the sort that seem to suggest not-quite completely harmonic partials in typical orchestral instrument sounds do indeed seem to be quite rare.