Using Audio In
The Audio In jack on Mopho’s rear panel can take audio from a variety of
sources, including line level signals and guitars. But what happens to it once its
inside and how do you get it out again? Simply plugging a guitar in does not
mean you will actually hear something when you play it.
Mopho’s basic audio signal path goes from oscillators to mixer to filter to VCA.
Audio In goes into the mixer. (Mopho has no pitch detection capability, so the
oscillators cannot track the pitch of the incoming signal. A pitch-to-MIDI
converter is needed to play the synth from a guitar.) So the External Volume
level must be up for Audio In to work. But you probably still won’t be able to
hear it. There are two potential obstacles in the audio signal path: the filter and
the VCA. If the filter’s cutoff frequency is turned down, audio does not pass
through. And if the VCA Level (Misc. Parameters) is down or nothing is gating
the amplifier envelope, no audio will pass through the VCA. The two most
obvious ways around the VCA are to turn the VCA Level up, essentially
bypassing the VCA, or use the sequencer to gate the envelopes. (You could also
use the keyboard to gate the envelopes, but then you start to run out of hands!)
There are two programs in Bank 1 demonstrating ways in which to use Audio
In. Ext In Env Filt (Bank 1 Program 127) is a simple envelope filter. VCA Level
is turned all the way up, allowing the audio to pass through the VCA. Both
oscillators are turned off; if they were on, you’d hear them droning because
VCA Level is turned up. Modulator 1 Source is set to EnvFollow (envelope
follower) and the destination is set to Low Pass (the filter). That means the level
of the incoming audio controls the filter’s cutoff frequency. Resonance is also
set at a moderate level, so you should hear a nice, squirty, blat at the peaks. For
low-level signals like a passive guitar or bass, you will probably need to turn
External Gain up to make it work properly.
The other program, Ext In Sequence (Bank 1 Program 128) uses the sequencer
to gate the envelopes for a pulsing, rhythmic effect. Press Push It! to latch the
sequencer on. Noise level is up, providing little percussive noise bursts. The
oscillators are still turned off. LFO 1 is synced to the sequencer and controlling
the VCA’s output panning. Sequence 1 is controlling filter cutoff. Again, you
may need to turn up External Gain for low-level signals. You can have a ton of
fun playing with just Mopho and patches like this, but if you sync to an external
sequencer or delay or both, things really get interesting!
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