[sdiy] VCO Linear Voltage

[Jerry Gray-Eskue]

<... will yield musically useful
intervals; e.g., fourth-octave-fifth, or third-sixth-fourth.>

Unless you are using a fixed voltage, or no 1/VO input, I do not get how
this works.
It would seem that the intervals would only work at a certain pitch?

- Jerry

-----Original Message-----
From: David G. Dixon [mailto:dixon at interchange.ubc.ca]
Sent: Tuesday, November 17, 2009 11:12 AM
To: 'Jerry Gray-Eskue'; Synth-diy at dropmix.xs4all.nl
Subject: RE: [sdiy] VCO Linear Voltage


I use the Linear FM input for playing tuned intervals with a square-wave
LFO.  If this square wave has +/- polarity control (as my LFOs do) then all
three settings of the switch (+, Full, and -) will yield musically useful
intervals; e.g., fourth-octave-fifth, or third-sixth-fourth.

Also, I concur that Linear FM is very useful for true FM effects.  Plus, it
is incredibly cheap and easy to achieve on most synths -- simply sum a +/-
voltage into the opamp which drives the reference current of the expo
converter, in parallel with the reference voltage.  In most (if not all)
cases, this will involve the addition of one resistor and one linear pot.

> I see how it would be useful in a LFO for envelope control, but I still do
> not get why it would be better for audio FM patches.
>
> If we setup a patch to vary the pitch at say 440hz by 20 cents using
> linear
> FM, one octave up at 880hz the variation is only 10 cents, two octaves up
> it
> is down to 5 cents. So how is this better than using the 1 Volt per Octave
> input for FM to vary the pitch at a fixed 20 cents for all frequencies?
>
> Is it just a "Cool" effect that people like?