On Friday 09 January 2004 20:21, Mark wrote:
> 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.
Ah, I see.
>
> 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.
Yes, that's what I just learned from Richards post. Never
new this, but it's an eye opener for me.
> 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.
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?
> 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".
I'm starting to understand this now.
I never understood the fact that I can apply an LFO to a DC
coupled (CV) input. I always assumed that an LFO must be a
DC signal, since it was used for DC coupled inputs. But an
LFO is just a slow moving audio signal, very AC. I didn't
understand. But now that I know that DC coupled inputs also
accept AC signals, the whole LFO issue is finally
understood. :)
Thanks,
Robert