Using Hardware Synths as Effects Processors

Hidden within the soaring vocals and incredible mix of David Bowie's "Heroes," is an extra bit of otherworldliness: Brian Eno's treatments of Robert Fripp's guitar. To help get that singular tone, Eno put Fripp's sustaining notes through a EMS VCS3, effectively using the synthesizer as an effects processor, adding what engineer Tony Visconti called a "shuddering, chattering effect" to the sound.

Take a look around the back of your synthesizer (or maybe even the front). If you're lucky, it'll have a socket labeled "Ext. In." or something similar that indicates it will accept an audio signal from an external instrument or mic source. What kinds of things can you pipe through your synth? Pretty much anything that makes a sound, from guitars and vocals to drum machines and even other synths. The possibilities are endless and limited only by your own creativity.

Although many synthesizers have the ability to process external audio in some form or another, it is a feature that is sadly underused. Harnessing the power of a synthesizer as an effect can be an exciting and unexpected way to add interest and movement to your productions, and can be used as subtly or as heavy-handedly as the job requires.

Hear the EMS VCS3 processing of Robert Fripp's guitar on David Bowie's "Heroes."

In this article, we'll discuss the different types of effects available on hardware synths for processing external audio, some suggestions for routing—an essential component of working with hardware—and touch briefly on gain-staging, or what you'll need to know to keep signals at the correct level.

Let's plug in.

Effect Types

Filter Effects

When The Who's Pete Townsend ran his Lowrey organ through the filter section of an EMS VSC3 (and again, later, with an ARP 2500), he created an utterly unique and therefore timeless sound for "Won't Get Fooled Again." Running external audio through a synthesizer's filter section is perhaps the easiest way to use a hardware synth as an effects processor, and yet it never gets old.

You get the best of both worlds: the tone of the original sound plus the filter characteristics of the synthesizer. Vocals, guitar, other synths, and especially drums can all benefit from seeing the inside of a filter. Modulation can also be employed to further shape the sound, giving it an alien and "how did they do that?" feeling. Sample and hold, should your synth have it, can be particularly interesting.

Many older mono synths allow you to filter external signals. The Moog Minimoog Model D is just one such example. Who wouldn't want to impart some of that luscious ladder filter tone to your signal? Modern monos can do this too. Arturia's Brute series of synths, such as the MiniBrute 2, all feature external ins, allowing you access to the famous Steiner-Parker filter.

The Inventory has an instructional video on processing external sounds with the MiniBrute.

Drive Effects

A recent addition to many synthesizers is the drive knob, an effect that adds grit and distortion to a signal. It's warm and fuzzy, and can be as subtle (for color) or devastating (for full-on meltdown) as you like. While most people will likely reach for a guitar pedal for distortion, there's nothing stopping you from making use of the drive circuit you already have in your synthesizer.

The aforementioned Brute series synths are known for their Brute Factor feature, a drive knob that can push the signal into seriously filthy territory. Korg's Monologue synth also has a drive knob that will affect incoming signal.

This feature is just waiting for you to stick other sounds through it. Got a hyper-clean FM sound that could use some roughing up? Brutalize it. Those wimpy drums need some beefing up? Into the synth it goes.

Once Upon a Synth has an instructional video on processing external sounds with the Monologue.

Reverb Effects

Everything sounds better through a reverb, right? There was a debate recently raging on YouTube on whether synth demos should be done through reverbs, as they perhaps unfairly sweeten the sound too much. But wherever you happen to stand on the issue, there's no getting around the fact reverbs sound nice. But can you use a synth to add reverb to an external signal? Many do now come with impressive reverb algorithms built in and some even allow you to affect outside sounds.

The Moog One features a lovely effects section courtesy of Eventide, and these effects can be used on any external signal (as can the filter too, natch). As if you needed another reason to covet a Moog One. If you'd rather not take out a second mortgage to get a One, the Access Virus T1 series also allows you to use its digital reverbs to process external audio. Lastly, if you'd rather work with an analog spring reverb, the Moog Grandmother has you covered.

Delay Effects

After reverb, delay is perhaps the most common effect. While there are lots of options for adding delay to a production, from pedals and dedicated delay units to tape echoes and plugins, you might not immediately think of a synth to fulfill your delay-based needs. However, you might have a nice delay unit in a synth you already have.

The Korg Minilogue is one of the most popular analog polys of the modern era, and part of its signature sound comes from its tape-style delay circuit. Luckily, the delay can be used on any incoming signal, adding that dirty, gritty effect to whatever you need. And speaking of dirty delays, one of our favorites is the Korg Monotron Delay. Believe it or not, this pint-sized synth has an audio input, allowing you to push anything through the delay. Beware though: it's pretty noisy, so it should be reserved for extremely dirty jobs only.

Chorus and Phaser Effects

Our tour of hardware synth effects continues with chorus and phaser. Chorus is a swirly, widening effect that first achieved popularity in the late 1970s. It sounds great on vocals, guitars, and, of course, synthesizers. Phaser effects also first started to appear in the 1970s, and can add an airy rising and falling effect to a signal. Both are lovely and neither are really associated with synthesizers, at least in terms of external audio.

Roland created some of the best-known chorus circuits with its SDD-320 Dimension D rackmount unit and Boss Chorus pedals like the CE-1, but you can get that gorgeous chorus effect with an RS-09. Basically a string machine, the RS-09 usefully has an audio in socket, letting you soak external audio in its bath of four bucket-brigade chips. For a modern—yet no less analog—synthesizer with phaser, look no further than the Dreadbox Abyss. It also has a lovely delay.

Pitch-Tracking Effects

Now we're getting into more esoteric territory. Pitch-tracking is when an instrument, like a synth or a pedal, reads the incoming audio signal and creates notes based on the pitch it detects. It was mostly used with guitars, although there's no reason why you couldn't use it with anything else that has a strong, defined pitch.

The Korg MS-20 (and re-release MS-20 MiniGR-300 and GR-700, as well as the SPV-355 P/V Synth, would be a better place to look. Although largely forgotten today, guitar synths were used by Pat Metheny, Jimmy Page, and others.

Left-Field Effects

Until now we've focused mainly on standard effects that exist outside of the world of hardware synthesizers. However, there's no reason that you have to confine yourself to the tried and true. Recently, thanks to the explosion in popularity of Eurorack and other types of modular synthesizers, left-field synthesizer effects have become increasingly more common. Granular synthesis, ring modulators, harmonizers, resonators—the sky is the limit.

How To Use Them

Using a hardware synthesizer as an effects unit is a little more complicated than just plugging in a guitar and playing a chord. Every synthesizer is a little different, but there may be some configuring that needs to be done. As the incoming signal is usually treated as another oscillator, the appropriate mixer adjustments will need to be made. Also, a key will need to be either held down or otherwise triggered to allow sound to pass through the envelope, just as with any other oscillator-generated sound.

If your synthesizer has an on-board sequencer that records motion data, like the Minilogue or Monologue, it may be possible to use it to add motion to your incoming signal, just as you would an internal sound. This will also get around having to hold down a key to allow the external signal to pass through.

When running external signals through a synthesizer, you may need to use a preamp to boost signals, particularly if it's a microphone or other non-electronic instrument. Synthesizers, drum machines, and other line-level components should be fine as-is though.

Lastly, we've focused on hardware synthesizers here but there's nothing to stop you from experimenting with using software synthesizers as effects processors inside your DAW. Many synth VSTs and AUs can be used as effects in the appropriate effects slot, so have a look and see if your favorite soft synth can be used as an effects processor.

Have your own favorite synths to use as processors of external audio? Let us know.


About the author: Adam Douglas is a musician and synthesizer fan based in Tokyo, Japan. He writes about synths on his blog, Boy Meets Synth.

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