[sdiy] Choosing a DAC

[John Loffink]

100 cents = 83.33 millivolts = 1 semitone.  1-2 cents is generally good 
enough for equal tempered scales, considering that everything except the 
octave is off by 2 cents or more anyway from the pure harmonies.

You will be limited in standard reference values.  2.048, 4.096, 5.000 
and 10.000 are common examples.  To scale just beyond 5 volts for 64 
semitones you will need to scale after the DAC, preferably with a 10 
turn or better trimmer.

You should get a 12 bit DAC with +/-1 LSB INL minimum, +/- 0.5 LSB is 
better.  13 bits with a 5 volt range would be ideal, but by then you 
would have to go with a 16 bit DAC, since 13-14 bit DACs are uncommon.

John Loffink
The Microtonal Synthesis Web Site
http://www.microtonal-synthesis.com
The Wavemakers Synthesizer Web Site
http://www.wavemakers-synth.com



stew wrote:
> Thanks for all the replies.
>
> I was more concerned about accurracy than resolution. Some 12 bit DAC's have 2 LSB intial error, whereas others have 0.5LSB.
>
> My plan is to have 64 note values (a bit more than 5 octaves). I could possibly change it to have more but I don't think it would be very useful (others might) and the pot (user input) resolution starts to become a problem. For example, using a 12 bit DAC I would multiply each note value by 64, so there would be 64 steps between each value that is output from the DAC. 
>
> I guess I'll have to use an adjustable reference. I was planning on scaling it afterwards but it would make sense to have the reference scale it.
>
> I'll have to think more about this when I get home from work...
>
> Regards,
> Stewart
>
>   
>