[sdiy] VA vs. RA: Square wave

[harrybissell at copper.net]

You are probably seeing the result of a series
capacitor used to remove DC offset from the
square wave.  The higher the frequency of the
wave, the less noticible this effect will be.

In most Analog VCO the square wave is DC coupled
so that it can be a modulation source. The "DC
blocking" cap is often at the VCF or VCA module.

Its possible to sum a Pulse wave with the PWM
input to remove the overall effect of DC offset,
the overall effect can be bizarre if you allow the
pulse to cut off completely.

The VA might be trying to simulate 'real world'
VCO waves

H^) harry



>
>
>---- Original Message ----
>From: controlvoltage at gmail.com
>To: synth-diy at dropmix.xs4all.nl
>Subject: RE: [sdiy] VA vs. RA: Square wave
>Date: Wed, 4 Apr 2007 11:22:09 -0400
>
>>Hello all,
>>
>>I have noticed in some analogue oscillators squarewave output, that
>>there is an unchanging time constant governing the loss of voltage
>>from the "high" state of the oscillator, such that at low
>frequencies
>>you actually see a gentle ramp downward in voltage from the start of
>>the cycle until the next reset, instead of a perfect square.  Since
>>this ramp downwards is not frequency-dependent (or not so much), at
>>high frequencies the same oscillator puts out a more perfect square
>>wave.
>>
>>Is this subtlety simulated in any virtual analogues, or do they tend
>>to output a perfect square wave the same shape at all frequencies? 
>I
>>am sure it would make a timbral difference.
>>
>>Cheers,
>>
>>Amos
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