VCOs for home-built modulars - update

SuperBAD MoFo mr808 at
Fri Sep 1 02:22:56 CEST 1995

On Thu, 31 Aug 1995 gstopp at wrote:

>      Oh cool you have a Chroma cuz I'm curious - what would you estimate 
>      the lowest possible VCO frequency to be? 

I'll hook it up to the ole'scope this weekend to figure out what's going 
on on the low & high ends.

>      Yah yer right even if the saw gets a flat spot around 15 khz the first 
>      possible harmonic is 30 khz so really it shouldn't matter spectrally. 
>      I concede that I probably sound like a waveform snob and should tell 
>      everybody that if I give the impression that I think that any machine 
>      is less expressive than any other that's not my intention nor belief.

I think that the lower harmonics have about the same energy as an
undistorted saw - up past the 3rd harmonic (somewhere around 50kHz), I
don't think it matters... 

>      I can't back this up but I think that human perception goes beyond 
>      20Khz. 

The easiest way to prove it is to get someone to tell the difference 
between a 15kHz sine & triangle - most people can.

>      Maybe it's just a tingle at the back of the neck or something 
>      that bypasses the ears but I swear there's something up there. If I 
>      frequency modulate one VCO with another and start hypersonic and come 
>      down, as I pass through the limit of hearing there are some wheeps and 
>      squeals that I can only get on modulars with good-lookin waveforms. 

Ok, I know what you're talking about...w/ filters that can go ultrasonic, 
my ears feel like they're turning inside out on an upward sweep, 
whereas if they're band limited (typical of digital anti-alias 
filters), things just kinda disappear.

>      I'm not sure how such things can make their way out of the 
>      reproduction system and into the air waves in the first place. Maybe 
>      it's some interaction that happens way up and I'm hearing the 
>      artifacts that splash down into the audible region. Anybody have any 
>      thoughts in this area?

Part of perceiving ultrasonics involves hearing the beat frequencies 
generated by ultrasonics interacting w/ other frequencies.  Of course a 
lot of the digital crowd denies that this is either possible or 


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