[sdiy] Additive/Subtractive synthesis?

[Magnus Danielson]

From: Ingo Debus <debus at cityweb.de>
Subject: Re: [sdiy] Additive/Subtractive synthesis?
Date: Mon, 28 Apr 2003 15:25:55 +0200

> Tim Ressel schrieb:
> > Just caught this on my weekly backlog flush. The
> > top-octave stuff I was doing is working, but I cannot
> > verify the frequencies. The cheap-a$$ counter I have
> > is not to be trusted.
> 
> You just need a reference frequency (digital synth). Feed that and 
> your output signal into a two-channel scope and trigger with one of 
> them. I use to tune my piano this way.

You should make them walk as slowly as possible in relation to each other.
Start with seeing one or a few multiples of the waveforms. Then "zoom in" with shorter
times if you want to be picky. This is how frequency counters reference oscillator
used to be calibrated.

If you have a scope, I strongly recommend this method, since it is very direct and can
easilly identify very subtle (in musical references) frequency differances.

A frequency counter is a great tool to determine frequency, but for lower frequency
trimming against a known reference the scope excells for the frequency trimmings we
are considering.

> If you don't have a scope you can still add the signals and listen if 
> they are beating (but opposed to the scope this won't tell you which 
> frequency is higher if they are not same).

The tip here is that if the beating gets faster as you turn, you turned in the wrong
direction. Trim until the beating is gone or at least very infrequent.

Cheers,
Magnus