[sdiy] VCO Tuning goals

[cheater cheater]

+1
also check out the latest expo converter thread

On Thu, Oct 1, 2009 at 11:02 PM, Ian Fritz <ijfritz at comcast.net> wrote:
> If you used an accurate VCO to start with you wouldn't need to ask these
> questions.  I have several designs that track to better than 0.1% up to
> 30kHz - 40kHz.  The largest error is always in the top octave. These designs
> are freely available.
>
> Ian
>
>
> At 01:07 PM 10/1/2009, David Ingebretsen wrote:
>>
>> In brief, I just finished building a trio of MOTM 300 ultra VCO's into a
>> Frac Panel
>>
>> http://www.xmission.com/~dingebre/page8.html
>>
>> As I have been tuning them, I have a question on the concept of tuning a
>> VCO.
>>
>> I understand all too well the scale will always have errors, and my
>> understanding is that an error of +/- 0.2% in the frequency is likely not
>> detectable, BUT... as one plays, it seems most successive notes are within
>> the same octave and often within a few notes. The question then is:
>>
>> Is it more important to have better accuracy octave to adjacent octave or
>> between 4, 5, or more octaves? That is, when I tune the oscillators,
>> should
>> I be more worried about a 0.2% difference between C0 and C1 or C2 and C3
>> than between C0 and C5? I hope this makes sense.
>>
>> I've been making a chart, and have been playing with Paul Haneberg's high
>> frequency trim modification
>>
>> http://www.wiseguysynth.com/larry/mods/VCO_track.htm
>>
>> or
>>
>> http://dragonflyalley.com/images/MOTM300/VCO_track.pdf
>>
>> (but I am using a multi-turn trimmer in series with a fixed 1M resistor
>> instead of swapping resistors).
>>
>> I've noticed there is some interesting interaction between the scale and
>> high frequency trim and I just want to make sure I'm approaching the
>> tuning
>> in the best musical sense. I'm curious musically/theoretically if it is
>> better to worry about the error between several octaves and let the note
>> to
>> note difference be what it is, or work on minimizing the "octave to
>> adjacent
>> octave"/"note to note" error. Reducing the high frequency error between,
>> say
>> C0 and C5, increases the inter-octave error between C1 and C2, or C3 and
>> C4
>> somewhat.
>>
>> The accuracy of the 300 makes some of this argument moot, but I am curious
>> about the whole zen of VCO tuning.
>>
>> David
>>
>> David M. Ingebretsen M.S., M.E.
>> Collision Forensics & Engineering, Inc.
>> 2469 East Fort Union Blvd. STE 114
>> Salt Lake City, UT 84121
>> www.CFandE.com
>>
>> 801 733-5458 Office
>> 801 842-5451 Cell
>>
>> dingebre at CFandE.com
>> dingebre at 3dphysics.net
>>
>>
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