[sdiy] Micro as a Linear to Exponential converter?

[Antti Huovilainen]

On Fri, 14 Aug 2009, Colin f wrote:

> In the case of the PIC I used, a couple of hundred bytes of RAM for a 
> 16-bit lookup table didn't leave much, so I had to put it in ROM.

You can easily reuse the same single octave. Just realize that when going 
down by an octave the frequency is halved -> shift the value right by one 
bit. It's important to store the highest octave and go down from that to 
keep the precision up (if you start from bottom octave you will have lower 
effective resolution in higher octaves).

Of course a better solution is to realize that the old 8 bit PICs 
(16F8xx series) are oooooold and even Microchip offers better chips in 
DIP cases.

> I added columns in the spreadsheet to calculate the rounding error as it
> went to 16 bits, which let me check the error in cents.
> That showed me 12 bits wasn't good enough.

Yea, 12 bits is definitely a problem for oscillators if you want large 
range. Again mostly a limitation of the DAC, not computing.

Antti

"No boom today. Boom tomorrow. There's always a boom tomorrow"
   -- Lt. Cmdr. Ivanova