From the manual: When processing external audio, you will first need to turn up the ExtIn Vol level in the Mixer. Otherwise no signal gets to the filter. Also note that the VCA needs to be open to hear the input. This can be done a number of ways:
1. Just turn up the VCA Level if you want the signal to go through continuously
2. Manually trigger the VCA envelope with the PUSH IT button or a MIDI keyboard
3. Select AudioIn as the mode in the PushItSw parameter, which automatically gates the VCA envelope with an input signal greater than a fixed threshold
There are also numerous other ways of opening the VCA using modulation.
Here are a couple other things you can try:
If you're going for your basic Mutron/Q-Tron-type effect, the best option seems to be to use the envelope follower to drive the filter cutoff, bypassing Mopho's envelope generators entirely. Starting from the basic patch, the general steps to do that are:
1. Turn the oscillators off (set the shapes to Off).
2. Turn the ExtIn Volume up.
3. Turn VCA Level all the way up.
At this point, audio should be passing through Mopho affected only by the filter cutoff level. You may have to turn up the Input Gain to get a decent level out of a bass or similar. Then, to get the envelope follower involved:
4. Set the PushIt switch mode to AudioI.
5. Route one of the 4 "mod slots" (for example, Mod 1) so that the source is EnvFollow and the destination is Low Pass.
6. Turn up Mod 1 Amount.
The envelope follower is now turned on and routed to the filter. The Cutoff has to be set fairly low in order for the envelope follower's effect to be heard. You'll probably also want to turn resonance up to get more "wow." And several of these controls interact, so tweak the levels to see what happens. You can also use different forms of modulation to get things really squirrelly or try using negative mod amounts and have the filter respond in the opposite manner (open to closed and back, rather than closed to open).
Other options are using the envelope filter to trigger Mopho's envelopes or using a sequence to modulate the filter for rhythmic effects.