[sdiy] Phase shifts and instantaneous frequency

[Ingo Debus]

Am 15.07.2008 um 22:26 schrieb Tom Wiltshire:

> I did try it, and as expected I hear a repetitive throbbing in the  
> resulting tone. The 1Hz effect is clearly visible in the wave;

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 ;-)

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?

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.

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


Another funny side note: the level meters of Logic move with 2 Hz  
while the level meter LED chain of my cheap mixing console move with  
1 Hz...

Interesting topic, indeed...

Ingo