[sdiy] Cheap Midi->CV

[Andre Majorel]

On 2005-09-11 01:25 +0200, Simon Brouwer wrote:
> Hi Andre,
> 
> At 00:32 11-9-2005, you wrote:
> >On 2005-09-08 22:50 +0200, Simon Brouwer wrote:
> >> At 00:01 8-9-2005, you wrote:
> >>
> >> >I don't need a frequency counter to know when a guitar string is
> >> >7.3 cents off. So yes, probably.
> >>
> >> Sure you can hear it while tuning your instrument (if my calculation
> >> is correct, at  e.g. 440Hz, a difference of 0.073 of a semitone would
> >> give a beat frequency of about 2 Hz). I wonder if you would notice the
> >> difference while playing, though, especially between different notes?
> >
> >I notice it while playing chords. And I don't have absolute
> >pitch or golden ears or anything like that.
> 
> So do you mean that after tuning with one of the strings off by 7 cents, 
> the guitar is noticeably out of tune during playing?

Yes. I pick the guitar. I play a chord. I wince and grit my teeth.
I pull out the chromatic tuner. One of the strings is 5 cents off.
QED.

This is something you experience all the time with guitars. They
get out of tune depending on the phase of the moon, if you have
new strings on, the humidiy changes, the temperature changes...
(Insert tempco/Moog joke here.)

> >> A couple of years ago I built a MIDI2CV using an 8 bit DAC, using 4LSB
> >> steps per semitone, for a range of 64 semitones (more than 5 octaves).
> >> I found this quite usable, not really out of tune.
> >> If I remember correctly, this DAC (a ZN426) had accuracy specified at
> >> better than 0.5 LSB which would be a factor 2 worse than a 12 bit DAC
> >> with 2 LSB accuracy if used for a range of 10 octaves.
> >>
> >> So I was feeling quite comfortable choosing a 12 bit DAC for my next
> >> project. I am not so sure about that now...
> >
> >Depends. Does it have one or several channels ?
> 
> Several, but only one for controlling the main pitch (the project is a 
> monophonic synth).

Then it's less of a problem. Accuracy is really important when
playing chords. For melodic work, I'd venture that most people
won't be bothered by 7 cents. If you're laying chords voice by
voice, you can adjust the pitch between takes.

-- 
André Majorel <amajorel at teaser.fr>
http://www.teaser.fr/~amajorel/