[sdiy] VCO Tuning goals

[David Ingebretsen]

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