[sdiy] Phase shifts and instantaneous frequency

[Ian Fritz]

At 01:43 PM 7/16/2008, Ingo Debus wrote:

>I tried it too, using Apple Logic. I think I got it right, it looks
>pretty much like Tom's waveform.
>
>I was going to write that perhaps something's wrong with my ears
>because I don't hear any modulation in the Hz range no matter how
>loud the volume is. There sure is something moving in that sound, as
>in a barberpole effect, or the decaying sound of a bass note of a
>piano (no surprise here).
>  But I don't perceive anything that repeats every second. When I
>turn up the volume, something on my desk starts to rattle with 1 Hz,
>that's all ;-)

Don't know if this is it, but I'm seeing that the effect is reduced if the 
volume is too loud -- some kind of saturation (?).


>But I just tried again, and now at high volume I perceive something
>like a very slight 1 Hz pitch modulation. This effect vanishes when I
>turn the volume down. Strange, huh?

That's expected, since the signal comes from a nonlinearity.


>So perhaps my ears are different from Ian's and Tom's, but perhaps my
>speakers are? I'm using Yamaha NS-10M. Whoa, that's it!!! Just
>pulling the plug out of my notebook so that the sound is reproduced
>by the tiny speakers in the computer rather than by the Yamaha
>speakers. And there it is, clearly to be heard, a nice 1 Hz
>modulation, like a Leslie cabinet.

Hmmm ... I hear it most clearly with headphones.


>My wife does hear the modulation even with the Yamaha speakers.

For me, there is a difference which ear I use!


>Interesting topic, indeed...

Indeed.  Probably not too important as far as synthesis applications, but 
it's strange that we were taught that harmonic phases don't matter.  All 
the old research results have just been thrown away?  Is it because we can 
only think about linear effects?

Ian