4046

[Synthaholic aka sPEW]

On Thu, 21 Nov 1996 21:01:49 -0800 (PST), you wrote:

>But let's say you have a synth at home.  With linear VCOs.  And let's
>say you want to fatten the sound with an additional VCO.  Okay great.
>Wouldn't it make sense to copy one of the existing VCOs, so at least
>any nonlinearities and temperature dependancies have a chance of
>tracking?

True, that the tracking problems inherent in any design would be
copied/canceled by this approach, however, I have built two other
VCOs, each of different design and I hear interesting phasing things
happen as I play differnet notes.  The VCOs' tracking is close enough
that the difference between them is small enough to be musically
useful.  I have found them to track for days at a time without having
to retune.

>I personally haven't done much with them, but here are some ideas:
>
>First know that this is a phase-locked loop chip, with two (three on
>the Philips version!) very different phase detectors with very
>different operating characteristics.  
>
>So the most obvious use would be to track other oscillators.

Done this: works well!  Ah, but it's output is *only* a square wave.
:)

>Or other sound sources.  
Need to try this.

>Add noise to the sound source for deliberate mistracking.  
Now this is a cool idea.  Noise could be used in at least two places:
1: mixed with the signal to be tracked.
2: low frequency noise could be summed with the loop filter output to
force jittery phasing.

>Screw with the loop characteristics for undershoot and overshoot.  
YES! This is cool!  Variable damping!

>Add a bias to the loop for phase shift.  
I have done this with an LFO.  When I tried summing a constant voltage
with the loop filter output, the comparator just compensates.
However, summing an LFO creates a nice phasing effect because the loop
lag charateristics force the PLL to play catch-up constantly. 

>Add a divider chain to lock on harmonics, subharmonics, and ratios.
I have used a divider chain to produce multiple harmonics of the input
(used as a freq mult), but never tried locking to harmonics of the
input.

>Use the xor gate to lock onto harmonics within a specific frequency
>range (something like Hammond foldback).  
I tried this and, well, I can take it or leave it.

>Combine the phase detector outputs together.  
Hmm...

>Run a whole string of 4046's one after each other and let their loop
>responses add.
Must try.  Probably can sound pretty wierd.

>My point that with all this cool stuff available, it seems silly to
>just use the chip as a square-wave only VCO module.

Perhaps it might be silly, but then some look at a canvas painted
black, with no other detail, and call it art...

Cool ideas.