MOTM

On 1/9/04, Robert van der Kamp put forth:
>I see. Is there also a low pass function applied on AC
>coupled circuits, at say 20 kHz?

It is a high pass filter, and the frequency is largely determined by 
the size of the cap.

(However, a capacitor can also be used in a different configuration 
as a low pass filter to reduce RF noise on low level inputs.  If no 
other filters were used, it would still pass DC.)

>Aha, that's why Paul recently said that only VCA #2 in the
>190 can be used for DC signals. That input must be DC
>coupled, while input #1 is AC coupled, I assume. So that
>means that input #2 of the 190 cannot handle DC shift and
>could cause pops in the sound. Correct?

I wouldn't say it couldn't handle an offset signal, but afaik, it's 
not going to remove that offset.

On 1/9/04, strohs56k put forth:
>
>An EG could be classified as a DC source or an AC source depending
>upon which part of the envelope cycle is active.  In the "off" state
>(at zero) and in the sustain state the EG outputs a constant DC
>voltage.  In the attack, decay, and release state the EG outputs a
>time varying voltage which is essentially an AC waveform.

Then you are using a different definition of the term.  The voltage 
between the output and ground does vary, but the current doesn't 
alternate.  I'm not trying to get into a semantic argument, but 
merely offer advice on using the system.

In practice, if I switch the capacitors in series with both inputs of 
the multiplier section of the 110, the output of an 800 does not 
result in a working VCA.  One input must be DC-coupled for what I 
consider a DC signal.  Likewise, I could patch the output of the 800 
to the audio input of a filter and trigger the EG to "ring" that 
filter, but I'm not going to be able to adjust a continuous flowing 
effect that follows the voltage of the EG.

>If an input is AC coupled, it rejects DC offset.  If we feed our
>"normal" -1 to +1 sine wave into an AC coupled input, there is
>essentially no change in the waveform.  (It remains a -1 to +1 sine
>wave.)  On the other hand, if we feed our 0 to +2 sine wave into an AC
>couple input, the DC offset of 1 volt is eliminated by the AC coupling
>and what results is a "normal" -1 to +1 sine wave.
>
>For DC coupled inputs, any DC offset remains in the signal.

Right, we agree on what is happening.  We can look at that as a AC 
signal riding on a DC offset -- that's what you would get if you 
summed a bias voltage and AC signal on DC-coupled mixer.