[sdiy] VCO Tuning goals

[David Ingebretsen]

Ian, 

Thanks for the suggestion. I know there are many designs out there and have
read the information on your site and looked at your designs as well, very
nice. 

Do you have any suggestions for my question though? I have several different
oscillators, each with different features and behavior. Some better
tracking, some less which is fine. I don't necessarily always want dead
accurate tracking. My question was really meant to be more to the general
"best" way to approach tuning to get the most musically useful VCO.

Thanks

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




~~ -----Original Message-----
~~ From: Ian Fritz [mailto:ijfritz at comcast.net]
~~ Sent: Thursday, October 01, 2009 4:02 PM
~~ To: David Ingebretsen; 'SDIY diy'
~~ Subject: Re: [sdiy] VCO Tuning goals
~~ 
~~ 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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