quantizer question

[Fraser, Colin J]

> -----Original Message-----
> From: gjalass at snafu.de [mailto:gjalass at snafu.de]
> Sent: 30 August 1998 08:05
> To: mark verbos
> Cc: Synth-DIY
> Subject: Re: quantizer question
> 
> 
> On Sat, 29 Aug 1998 22:48:46 -0600, you wrote:
> 
> >In looking at Chris list's ARP style quantizer, I can't help but
> >ask if one could get away with using a cheeper 8 bit D to A
> >converter. One that is like $3 insted of like $23? Since only 7
> >bits are used anyway.
> >
> >is there a good reason why not?
> 
> please keep in mind that DAC's do have tolerances ( e.g. 1 LSB - Least
> Significant Bit ). Since it's required to quantize to e.g. semitones
> You do need a very "good" DAC to keep audible errors to a minimum.
> Therefore only the MSB's of the 12-Bit DAC are used.

I have used various 8 bit DACs (ZN428, ZN558) to output CVs in various
units and never had any problem with 'tolerance'.
You just have to apply a bit of gain to the output of the DAC so that a
1 bit step = 1 semitone (83.3mV for 1v/oct).

A 12 bit DAC allows 3 or 4 octaves of Hz/V type output if you use all
the bits (and a lookup table).

The average error in a quantised *continuous* signal will be at least
1/2 LSB - maybe this is where people get the idea that an 8 bit DAC has
poor tolerance.


Colin f