[sdiy] Attempting the impossible?? Detuning waveforms?

[Scott Gravenhorst]

harrybissell <harrybissell at prodigy.net> wrote:
>Usually sub octaves are made by digital division (divide by two or four).
>
>If so, you cannot directly detune them, they are phase locked.
>
>You could synthesize a sawtooth wave, then make a 'sawtooth phase shifter'
>
>(see Magnus' site).  These could give an 'animated' effect though it would
>
>NOT be truly detuned.
>
>Or you could do a phase-locked loops (see Scott Gravenhorst's 'Fatman'
>pages).
>It will take some time to follow a new frequency input, but that might
>make it more
>animated. 

Speaking from experience, yes, it takes time - however with a proper loop
filter, this time can be made very small, imperceptibly small given
reasonable jumps in frequency.  My PLL circuit handles more than octave
jumps quite well without overshoot or audible glitches.

>The PLL will try to lock exactly as well, you would have to add
>some
>CV to force it to unlock.

Yes, depending on the loop filter, you can nudge it off frequency for a
while (a DC offset would be compensated by the phase comparator).  I have
summed an LFO with the PLL's pitch CV and it does push it off frequency
similar to modulating a plain VCO with an LFO.

Regarding detuning: what I have contemplated, is using PLL a little
differently.  If the input of a PLL is driven by an XOR gate with a VCO
square output driving one input and an LFO square output driving the other
input, wouldn't the LFO cause extra phase reversals that would slightly
increase the PLL output frequency?  And wouldn't the amount of increase
depend upon the frequency of the LFO?  The loop filter would be important,
I'm sure.  I'm not sure how useful this would be tho, prolly why I haven't
tried it.


>The easiest way would probably be to build a second VCO...

I would agree with that.

>H^) harry
>
>Jeff Farr wrote:
>
>> Ok, I've got myself a kitten here (not the furry kind).  It has only
>> one osc, But each waveform has a volume slider before being sent to
>> the filter.  It's also got a sub osc, and a sub-sub osc.  I've already
>> added the Op-Amp circuits to patch out the inputs to the filter and
>> it's modulation sources, and added an individual out for each waveform
>> (and sub).  I'm currently working on adding a VCLag to turn the
>> normally square subs into triangles and other funky shapes, I prefer
>> the more suble harmonics of a tri for subs and the sub-sub makes a
>> cool 'harmonic' audio freq LFO.  Now, what would be MEGA cool is being
>> able to detune each waveform slightly for a thicker string sound.
>> Even better to detune the sub-sub as a LFO.  Is this even possible?
>

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