[sdiy] more on which VCO (low fi "electro" ones)

[Scott Gravenhorst]

Linium <intent at netpratique.fr> wrote:
>On Sunday 13 June 2004 00:10, Scott Gravenhorst wrote:
>> If you look at VCOs that can track a CV, you'll find that they generally
>> exist in two flavors: triangle and sawtooth.  They track a CV because they
>
>I have yet to go in the "inside" of vco design, but i am following the recent 
>discussions here, slowy accumulating informations. 
> 
>> have linear ramps.  It is this fact that makes them musically useful.  An
>> example of a nonlinear VCO would be a multivibrator that uses a simple
>> resistor to charge the integrating cap.  Here, you have an exponential
>> curve instead of a ramp and while this will sound different from a ramp, it
>> will not be musically useful in that it won't track the CV linearly.  In
>> less than an octave it will be "out of tune" with a standard scale.
>>
>Aren't the OB8/X/Xa said to have unperfect saw wav, a little curved cause of 
>the not linear charging ramp of the capacitors ? Would this explain the 
>fattnes for wich they are reputed ?

I have no experience with that machine, but "fatness" is a really difficult
characteristic to nail down.  When I think of "fat" sound, it's not so much the
waveform of a single oscillator, rather something like two oscillators that are
at *slightly* different pitches so you get a phasing sound.  Other people might
say "fat" is something else altogether.

>
>> I think what you're after isn't really called "low-fi", rather you want is
>> to screw up the waveform so that it's no longer a ramp or a triangle.  But
>> you also want the sound's pitch to track a CV so that it's musically
>> useful.  
>I said "low-fi" because i like when the VCO drift, it sounds like "Board of 
>Canada", like an old vynil or tape that suffered from time ;)
>Well in fact i have built my own DAC for my soundcard, so now i can produce 
>any DC voltage with 16 bits resolution and use my computer with Puredata to 
>create an array that would store the voltage necessary to play any kind of 
>detuned or not exactly exponential VCO core.
>But in fact, detuned effect alone could be obtained with a simple modulator on 
>a perfect VCO, just that if it is a tradoff for reviving some kind of ancient 
>vco core technology i am ready to cope with it.  May be It offers more 
>experimentation playground, the last thing would be that some weird VCO 
>exist, possibly with funny or unusual, if not unconstant waveform along 
>pitch, and that the sound is interesting enough :)
>
>The way this is done in the modular world is to use a good VCO
>> into waveshapers and filters.  Waveshapers come in many varieties and many
>> members here have schematics for all kinds of them posted.  Hardsynch is
>> another method for screwing up a waveform and maintaining musical
>> usefulness and it sounds interesting.  Pulses and squares are easy to make
>> with comparators and they sound characteristically buzzy.  Filters can then
>> further contour the waveshape to give you an infinite variety of different
>> timbres.
>>
>I have the Wavefolder from Oakley wich is a waveshapper, well i need to repair 
>it since a long time, but then it will try it again.
>Theses days i have been setting up a dual moog rogue VCO clone, and i 
>experimented a little with sync, yes it is a nice effect (that i knew only in 
>the digital world until this afternoon) to get buzzy screwy  fat tones. :)

Ah yes, well the ears will tell you.  It sounds like you have the spirit of this
stuff working, just keep messing with things and you'll discover good sounds.

As far as weird or ancient VCOs go, it occured to me that you can take a nasty
VCO that won't track a CV well and use it as the VCO of a phase locked loop,
then use the PLL to lock onto a well behaved VCO, but use the sound from the
nasty one.  That way, you get the well behaved pitch behavior of the good VCO,
but the sound will be from the nasty VCO.  -- If you don't object to a PLL.  (I
like them...)

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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