[sdiy] Moogey jitter

[Richard Wentk]

At 03:44 16/04/2006, you wrote:

>The link below is a magical moogy sawtooth wave spliced into a cold,
>perfect, digitally stable, un-antialiased sawtooth generated in CoodEdit.
>It switches back and forth several times.  Remember, this is the most
>extreme difference in the world theoretically.  But there is virtually no
>audible difference.

This depends how good your ears are. I can hear a difference quite clearly. 
It's not ultra-obvious, but you won't get the Moog Sound [tm] just from the 
VCOs.

>Measuring jitter means nothing unless one compares it to other analogs.
>
>http://home.att.net/~elhardt5/Sawtooths.wav

If you do a spectral plot in Cool Edit, you can see two things very clearly.

The first is a random-ish amplitude modulation. I wouldn't be surprised if 
this were supply related, and the 'jitter' is actually coming from the 
other VCOs and LFOs.

I could be wrong about that, and the only way to find out is to pull a VCO 
out of its rack and check it on its own.

The second is very subtle random pitch drift. It's hard to see with an FFT 
because the pitch resolution is poor down at the fundamental, but I'd guess 
it's a few cents or so.

Both of those taken together will combine to create a randomised chorus 
effect when more oscillators are added, especially in the mid/upper range. 
Add more nonlinearities because of the VCF and VCA stages, and you have a 
significant timbral effect.

I have no idea what Kevin's history is on AH. And to be honest I'm not 
really interested. But I am interested in the fact that after 40-odd years 
no one has yet managed to exactly copy the Moog sound without using Moog 
circuitry. Since it is such a distinctive sound - I don't think anyone is 
arguing that it doesn't exist - I don't think trying to work out what 
creates it is entirely a waste of time.

Richard