[sdiy] Moogey jitter

[Ian Fritz]

At 12:35 PM 4/16/06, René Schmitz wrote:


>So even when I can't hear much of a difference on the plain wave, there 
>might still be things that show up after processing. (The digital wave 
>seems to have a little "more bottom", while the VCO is a bit more "bright".)

Perhaps.  The spectra aren't exactly the same.  I thought I heard the same 
thing as you until I leveled the amplitudes.  Now I don't hear it.  But my 
ears are no longer young.  :-)


>>The amplitude variations seen in the Moog waveform are due to small 
>>transients at the switching point of the waveform.  These come and go at 
>>a rate of ~5 Hz.  I can't hear any modulation at that frequency, and I 
>>believe the spikes are inaudible artifacts. But people will always say 
>>your data has am noise on it anyway, I'm sure.
>
>Could be a sampling artefact. Some of the high frequencies of the fast 
>transition might be aliased down.

Seems to be.  There is finite amplitude at 20kHz, but quite weak.


>>I used Sound Forge to resample and interpolate the waves at 4*44.1 kHz.
>>With this done there are transients at all the switching points and they 
>>are all nearly the same.  So there is very little amplitude variation.
>>I measured the Moog period at five different points with a resolution of 
>>.01 ms.  The periods range from 10.28 ms to 10.30 ms, a variation of 
>>0.2%.  If the jitter is a fixed amount of time, then it would be 2% at 1 
>>kHz, which might be audible.
>
>But it will surely turn up if you use several oscs beating against each other.

Doesn't seem to (see next post).

   Ian



>Cheers,
>  René
>
>--
>uzs159 at uni-bonn.de
>http://www.uni-bonn.de/~uzs159
>