digital control of analog component question...

[KA4HJH]

>The troubles start when you want very precise control... you either need a
>very good 8 bit DAC (Midi for instance is 0-127 or 7 bit...) or a DAC with
>high resolution and a "lookup" table to get the right values...

And if you want to implement exponential D/A you'll need 14 bits to 
get about the same resolution as a 7 bit DAC and an analog expo 
convertor. Ugh! OR do a lot of range-switching a la the PAiA method.


>The other problem is "zipper" or step noise... when you move a value through a
>linear range (especially an oscillator or filter sweep) you hear jumps in the
>audio (like a zipper...)

Ironically, what this means is that you can *get away* with using a 
relatively cheap and simple 8 bit DAC to control base pitch, but when 
you start doing real-time modulation you'll need at least 12 bits to 
hide the zipper noise (these days if I was designing a 
*general-purpose* device from scratch I wouldn't waste my time on 
anything less than 14--head for the Maxim sample page). You can 
always scale a pitch-bend voltage down and limit its range, 
increasing the effective resolution, but if you want digital 
envelopes and LFO's...

>Really good programming chops can cover most of this up...

It doesn't hurt.


The other problem is when you have something that isn't 
voltage-controlled to begin with, but that's another thread.

Terry Bowman, KA4HJH
"The Mac Doctor"

ICQ: 45652354