Running external signals through a synthesizer...

[Blackie1]

I don't have any synths at the moment, but I had a Micromoog a while back that I sold, unfortunately. I didn't realize until long after that it's possible to process an external signal (like a guitar) through the synth. Now I want to get another Micro, both to get my old Moog back and also to give this function a try - seems like it might open up lots of processing possibilities.

But what I want to know is how the synth (not necessarily just the Micromoog, but really any synthesizer with an external audio input) processes the sound. Would it just be the synthesizer's filter that would manipulate the incoming signal? Or would it be possible to do things like add noise to the signal with the synth's noise control, use LFOs in conjuction with the rest of the synth's architecture to effect the sound, etc. Maybe even envelope controls would be able to alter the guitar's ASDR? Maybe not at all, but I don't know, and that is why I am asking!

Any help would be appreciated!

Thanks

[Z]

The external input on synths simply mixes an external sound along with the synth's oscillators through the synth's filter and amplifier. You can turn the volume all the way down on the synth's oscillators to only hear the external input through the filter and amp.

If the synth does not have an envelope follower for the external input, you will need to play the synth's keyboard along with the external input.

Here's a couple of videos I made demonstrating processing an external instrument (drum machines in both instances):

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[Blackie1]

Thanks very much for the help. Those videos were quite informative.

So basically when something is plugged in to the external input, the only section of the synthesizer that will have an effect on the sound (apart from volume controls and the like) would be the filter, right?

[balma]

Lots of synths have line in functions and you can use advanced functions to process external sounds depending of wich gear are you using.
You can go from processing a line and create slicing sequences (included on all Electribe models) to try several ring routes to combine it with oscillators, to implement filters, effects, motion sequences etc, to the input signal.

[Henfield]

The biggest problem with using the external input is that you normally cannot trigger the envelope generators, so the VCA cannot be opened, so there is no sound unless you trigger the synth via the keyboard or a sequencer. The Micromoog is more versatile than most older analog synths for running an external input through the filter, as you can take the VCA out of the signal path. You can then use the filter, along with the LFO to modify it.

Alternatively, you could use the Moogerfooger MF-101 Low Pass Filter or the MF-107 Freqbox, as they both have envelope followers built-in to follow the dynamics of your playing. You could patch the output of the Moogerfooger envelope follower to control the cutoff of the filter on your synth, if there is a filter control input on the synth.

The other option is to go modular. Their are modules, such as the Eurorack size Doepfer A-119 or the 5U size Synthesizers.com Q118 Instrument Interfaces. These interfaces can amplify the audio up to modular levels, they have an envelope follower buil-in, and most importantly, they have trigger or gate outputs that can trigger envelopes for VCAs and filters. You can start a small modular system to augment your analog synths, or just use a modular for processing external audio.

[Walter Ego]

Or...

You can just *cheat* and get a couple Korg Monotrons. The filter has no envelope control, but you don't need to do anything to it to run audio through the VCF. I don't know if that's the case for the original Monotron, but it sure works nicely on the DUO and DELAY models. Just plug and play. With the DUO, you don't get a filter LFO as on the original, but you do get a nice CUTOFF/RES (PEAK) control. With the DELAY, you only have CUT, no RES (and there is an LFO, but not for the filter), BUT you do get that oh so nasty SPACE ECHO style delay. With how cheap these things are, you can't go wrong. You get instant access to MS-20/MS-10 sounding filter, and it's room shaking. It has also not been a problem to just chain both 'trons together to get the benefit of both filters and delay FX. If you want drums that sound like they just landed from Flaming Lips' Yoshimi, that's all you need.

Walter

[nvbrkr]

It's just the filter that affects the sounds.

BUT you can use things like the lfo or the noise generator in conjunction with it too. That is, if the synth allows those to be routed to the filter section (many "bigger" monosynths allow this). It results in similar choppy, oscillating, S&H controlled etc. sounds as when using the synth's own oscillator section. Not necessarily with a very pleasing quality of sound though. For example, rompler patches may sound quite thin and distorted when driven through my Voyager's filter. Still worth the try every now and then.

[pflosi]

Or...

You can just *cheat* and get a couple Korg Monotrons. The filter has no envelope control, but you don't need to do anything to it to run audio through the VCF. I don't know if that's the case for the original Monotron, but it sure works nicely on the DUO and DELAY models. Just plug and play.

Same on the original. Every once in a while I plug a cheap FM radio into the monotron to annoy the visitors in my flat

[Bitexion]

Many synths let you bypass the VCA with an "initial level" knob, which basically just makes whatever comes from the filter drone on forever. That should work with external signals without having to press a key to let it through.

[pflosi]

On some (semimodulars), like the MS10 / 20, you can also patch the VCA to be open all the time...