On 1/9/04, Richard Brewster put forth:
>Good question about the EG output. It is DC coupled, for the reason
>above. However, an envelope is a type of AC signal, because it changes
>over time. The interesting thing about an envelope is that it combines
>different frequencies in one cycle. Attack is typically fast, decay and
>release slower. An attack time of 20 milliseconds is 1/50 of a second,
>i.e. 50 Hz, up in the AC range for sure. But a 500 millisecond release
>time is only 2 Hz. So it is an AC signal with some very low frequency
>parts.
The output of an MOTM 800 is not an AC signal. It is a positive
voltage that never crosses zero. AC stands for "alternating current"
-- it "pushes" current one way when the voltage is positive, and
"draws" current the other way when its voltage is negative.
Most audio inputs are AC coupled. Their inputs have "blocking
capacitors" to remove DC offset. Most CV inputs are DC coupled --
they can accept both AC and DC signals. There is a difference
between AC and DC coupling when doing ring modulation, oscillator FM,
etc., but understanding this difference is very important when using
patching filters and VCA's. The modulation inputs are DC coupled,
but the signal inputs are usually AC coupled.
For example, one VCA in each of the MOTM dual VCA's can be used to
process control voltages (the 110 has a switch allowing you to bypass
the capacitors) so that they can be used to control modulation depth.
The other VCA in each dual VCA is AC coupled, so it can only be used
to process audio signals. The 820 lag processor functions as
DC-coupled low-pass filter. It can be used to process control
voltages and audio signals. Afaik, all of the other MOTM filters
have AC coupled inputs, so they cannot process control voltages. If
you try to ignore this, your patch won't "work".