[sdiy] MIDM-CV DACs, Part #3 (last)

[Colin Fraser]

----- Original Message -----
From: <jorgen.bergfors at idg.se>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Thursday, September 19, 2002 7:39 AM
Subject: Re: [sdiy] MIDM-CV DACs, Part #3 (last)


>
> Although this theoretical discussion probably is correct, in reality a 12
> bit DAC is more than enough.
> I have built the Oakley MidiDAC, which I believe is based on a 12 bit DAC.
> I have measured every single midi note value with a 4 1/2 digit DVM. The
> accurracy is way better than you could dream of tuning a piano or guitar,
> for instance.

Paul S dictates authoritatively that you need your DAC to have an error of
less than 1% of a semitone.
Assume you have 1 oscillator tuned to 256Hz (2 ^ 8)
We want a second oscillator at the same frequency, but, oh no !, we have a 1
cent error !
Our actual frequency is 2 ^ 8.000833 = 256.148 Hz.
So we have a beat frequency of 0.148 Hz - that's about one beat every 7
seconds.
Wait a minute - at maximum DAC error, my synth sounds better ! (assuming my
oscs don't soft sync that close)
That can't be right !

Colin f