[sdiy] various scales for a Midi-to-CV ??

[harrybissell at copper.net]

OK Temperment then... :^)

You could not use the MiniWave for that, it would not
have the resolution.

I think that most VCO ~would~ have the resolution to tell the
difference between tempered notes. The Prophet V had a 12 bit
A/D converter but I think the tuning was more like 14 bits. You
could hear the difference.

At the time it was the favorite of all the local Arabic bands
so they could get authentic scales

H^) harry



>
>
>---- Original Message ----
>From: usenet at teply.info
>To: synth-diy at dropmix.xs4all.nl
>Subject: Re: [sdiy] various scales for a Midi-to-CV ??
>Date: Tue, 08 May 2007 00:02:26 +0200
>
>>harrybissell at copper.net wrote:
>>> Are you talking about "tunings / temperment" or "scales"
>>> 
>>According to what you wrote below, i'll rather be talking about 
>>temperment than scales, even though both terms are (at least in my 
>>opinion) somewhat related to each other. What i mean with that wille
>
>>become clear a couple of lines below.
>>
>>> Temperment is the actual frquencies used...
>>> 
>>> "Pythagorean tuning" uses whole number ratios related to the
>>> harmonic series i.e. a fifth is a 3/2 frequency ratio
>>> 
>>> "Equal Temperment" has modified the frequency of the fifth (etc)
>>> to permit playing in ~any~ key
>>> 
>>> Some of the Arabic tunings you mentioned have non-western
>intervals...
>>> 
>>> Scales, on the other hand... are selections from the available
>>> pitches. Things like "major", "minor" etc have different half /
>>> whole steps.
>>> 
>>I absolutely agree with you here. Given an equal temperment, one
>could 
>>play different scales with all the same frequency values. Say you
>got 
>>some fixed frequencies according to C Major. With that same values,
>one 
>>could also play A Minor or all those different modes like d Dorian
>or F 
>>Lydian or e Phrygian and all that. But that's not quite the point
>i'd 
>>like to address.
>>
>>> Assuming you want 'temperment' you could make up an offset table.
>Rev
>>> 3.2
>>> Prophet V allowed you to use the twelve knobs in the center of the
>>> unit
>>> to tweak the twelve notes +/- a small amount (one half strp iirc).
>>> 
>>> If you want to make 'scales' I'd use a MIDI-CV converter driving a
>
>>> programmable A/D - D/A such as the Wiard-Blacet MiniWave.
>>> 
>>Sounds like a good idea to me. What i was thinking about was some
>sort 
>>of #2 just omitting the A/D part and doing soem calculations in a 
>>microprocessor instead so one can have a MIDI-CV converter with some
>
>>selectable (and maybe user-defined) scales. What i'm not quite sure 
>>about is (given the CV-controlled oscillators around) whether or not
>it 
>>is worth all the computation of frequency values (and Voltages
>according 
>>to that) if the change in frequency is quite small (probably less
>than 1 
>>percent or less than a couple of millivolts for a 1V/octave law). Or
>in 
>>other terms, are the oscillators around good enough to get
>reproducible 
>>frequency shifts for those small changes in CV Voltage. Another
>(maybe 
>>more complicated) option would be to build some sort of
>MIDI-controlled 
>>DDS oscillator, which could have the advantage of some user-defined 
>>waveforms and frequencies using some sort of lookup table. Actually
>that 
>>was the thing i was thinking about initially. But with oscillators
>good 
>>enough around, there would be no need to reinvent the wheel, ya know
> ;-)
>>
>>Greetings,
>>Florian