[sdiy] Expo converters, lin log etc.

[Eric Brombaugh]

Nicholas Gregorich wrote:
> 
> On Jan 31, 2007, at 5:47 PM, Tom Wiltshire wrote:
> 
>> This is essentially a 20-bit definition of pitch (7+14 with 1 bit 
>> 'overlap'). 24-bit ADC/DACs are fairly commonplace and cheap. So my 
>> answer to the question is "No, we probably don't need to exceed the 
>> pitch resolution of MIDI, but while we're at it, we might as well use 
>> 24 bits not 20."
> 
> I think many of the 24 bit ADCs and DACs out there are delta sigma, not 
> so useful for this application (no DC).

I've got no experience with delta-sigma ADCs, but the delta-sigma DACs 
I've used are perfectly capable of generating DC. The big problem you'll 
have with them is that they're typically designed for audio output 
levels (~2V p-p), so in order to take advantage of 24-bit resolution you 
need CV processing circuits that are accurate to 0.1 microvolts (2V / 
2^24). Regardless of how inexpensive the data converters are, designing 
analog circuitry with that level of noise & offset nulling is pretty 
tough to do.

Eric