[sdiy] Gated VCO cycles

[harrybissell]

Peng wrote:

> A gate input where the VCO is off until a gate is received, then it
> starts it's cycle. when the gate is turned off the VCO finishes it's
> cycle before going off (see page 7). I want to implement this feature
> in some of the VCOs I'm building, but I'm not sure how to accomplish
> this. Should I be looking at the switch in the VCO core?
>
> yes.  This should be quite easy with a sawtooth core.  Jam the reset
> line high with
> a flip-flop.  Let it go low when you reset it, and let the comparator
> drive it back high.
> I'm not positive but I suspect the right polarity of R-S flip-flop
> would work... when the comparator pulse comes it will still get
> through to the reset transistor (or fet).
>
> This would use the 'disallowed' state of having both set and reset
> true at the same time. Both outputs will go 'high' then
>    I'm thinking this gated on/off could solve two problems I have with
> my synth. One being: how to keep my LFO in time with live impro drums
> ? For example: I'm using a +/-5V sine to modulate cutoff on a VCF. On
> every key gate I would like it to modulate the frequency up before
> (reset). This way, if I get the lfo speed close to the drummers tempo
> the modulation sounds better (more locked).
>
> this might be more like soft sync than gated VCO...  ???
>    Second problem would be the sharp clicks and pops I get when
> playing low bass lines, especially when the waveform has low harmonic
> content, like a sinewave. They kinda come and go randomly with note
> ons and sometimes note offs. I notice this with other synths with free
> running oscillators and even a lot of software synths. Are these
> clicks/pops the result of non-zero cossings (sorry for the sample
> editing speak)? I can supress the clicks with EQ but that's not always
> desirable.
>
> hmmm... if you used a sawtooth core, and made a triangle with it, and
> then a sine...
> the sine wave would always stary at one 'peak' ... exactly the
> opposite of what
> you want.
>
> Of course you CAN do it... just more complex
>
> H^) harry
>
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>     Any info, advice, comments,ideas are desperately needed and
> greatly appreciated. ThanksPeng
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