[sdiy] Attempting the impossible?? Detuning waveforms?

[Bob Weigel]

hehe...without taking time to draw it all out and actually think about 
it...I'd vear towards Harry's analysis.  Those doggone speculations 
though. :-)  Actually I think speculations are fine and that's often how 
we grow together..so long as they aren't..say..speculations about 
people's character and that kind of thing. .  I'd think it would be a 
dull group of people didn't speculate now and then...so long as from 
context you can tell it's a speculation from reading the article. 
      But anyway..yeah I mean I can't imagine getting any kind of signal 
that I'd want to listen to from any kind of convoluted attempt to pitch 
shift signals.  I think Chris's extra oscillator mod is a more useful 
expendature of time.  I mean..by the time you build the circuitry to 
shift the pitch of an oscillator..you could have pretty much just built 
another oscillator that would sound better and respond more pleasantly. 
The true independence of oscillators is what we love about having two or 
more primarily I think.  Even when the waveforms themselves are created 
in somewhat of a convoluted fashion (Say a Siel DK600, DK80 or the 
Polymoog) having two independent analog oscillators at the root of it 
all creates a special beautiful fascinating quality.  But..alas I'm 
speculating again. Someone talk to me real mean and nasty to prove how 
out of place I am and I'll go give myself a swirly.  -Bob

harrybissell wrote:

>Scott Gravenhorst wrote:
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>>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.
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>>
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>hmmm.  I don't think that would work.  Yes there would be extra phase reversals
>but there would also be a lot of jitter. The LFO would not be syncronous with
>the VCO
>and the PLL would not be able to reconcile them.
>
>I'd think of it as the XOR gate is a balanced modultor... the output should
>contain
>sum and difference frequencies. If you higpass filter that, you might get rid
>of the
>difference and have only the sum.  It would work OK for sine waves, but with
>square
>waves it would be really tough.
>
>By the time you are done you'd have a frequency shifter...
>
>I'd sooner get out the BBDs and use them !!!
>
>yep, build another VCO.   ;^P
>
>H^) harry
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