[sdiy] lookup table as expo converter

[Ingo Debus]

Am Dienstag, 25.05.04 um 00:29 Uhr schrieb Tim Ressel:

> Tim don't know compression. Tim just bang rocks
> together and make wavetable.
>

Here's an easy way how to do it with a small table:
Take the ADC value, subtract the binary equivalent of 1 volt, do this 
as often as required to get into the range between 0 volts and 1 volt. 
Count how often you had to subtract, this gives you the octave you're 
in (assuming the input is 1volt/octave). Then use a table to decode the 
remainder. If you only need semitone resolution, this table has just 12 
entries. The octave gives you a multiplier, say 1 for lowest octave, 2 
for next octave, 4 for next octave and so on.

I used a similar technique (just the other way around) in my 
pitch-to-MIDI converter.

Ingo