“Electric Avenue” was one of the biggest MTV hits of the ’80s, and still gets crowds bumping on the dance floor. Recently I had to recreate its synth parts for a cover band’s backing track. Listening, I realized the trademark “engine-rev” sound wasn’t a synth, but actually delay effect feedback.
Delays “store” incoming sounds and replay them at a settable later time. To get repeats, some of the delayed signal is fed back into the input. If the feedback is high enough, the delay will self-oscillate, like how a mic feeds back when pointed at a speaker. This can turn into something that sounds nothing like the original input. By adjusting the delay time, you can “play” the pitch of this monster noise. This is what’s behind the “Electric Avenue” motorcycle rev.
Be careful when cranking up feedback with hardware or software delays! Volume can get out of control and blow speakers, amps, and ears, so turn the master volume down for safety. Scroll down for online extras, including a signal diagram and audio examples.
1. Any delay will work, but different types have different tones. “Electric Avenue” sounds like an ’80s analog “bucket brigade” delay. For this example, I used my Electro-Harmonix Stereo Poly Chorus re-issue. Though it’s called a chorus, under the hood it’s a short analog delay, and makes great roaring sounds — and lots of other watery weirdness! You can use newer digital delays, but old-school analog and tape delays typically have the tastiest feedback.
2. Here’s the weird part. It doesn’t matter too much what your initial input sound is, because the delay’s own feedback tonality is so dominant. Try a quick, bright synth bass; anything brief with a wide range of harmonics should be fine.
3. Set the delay time close to maximum and the repeats about halfway up. Play a note. Now try cranking the feedback almost all the way (again, watch the volume). Once it’s feeding back without you holding a note, play with the delay time knob. This should get you into “engine revving” territory.
4. It takes a little time for the feedback loop to bloom harmonically. Because I wanted to record many passes of revving sounds without playing a note and starting over every time, I left the delay in infinite feedback and improvised a gate so I could turn the sound on and off by playing keys on my modular synth. I fed the pedal output to the synth's VCA and controlled it with a simple on/off envelope triggered by the keyboard. Now I could play the keyboard with my left hand and twist the delay time knob with my right.
5. You can do the same in a DAW by setting up a simple synth with a delay insert effect, followed by a noise gate with a sidechain input. The main channel would use a synth with a brief tone for the delay input. On a second track, insert a synth with any simple on/off sound (such as an organ) and select its output as the input for the noise gate’s sidechain. Play a note on the first synth and crank the feedback. At first, bypass the gate so you can hear the delay feed back. Now, un-bypass the gate, switch to the second synth, and use it to “play” the effected sound.
Online Extras - Notes, Diagram, and Audio
The idea with this patch is to create analog (or digital) delay feedback and adjust the delay time in real time to change the pitch of the "engine rev," and additionally set up a keyboard as an "on/off" switch. This way we can play in time with a track with the left hand, and twirl the delay time knob with the right hand. Obviously, you'll want the delay to be next to the keyboard, not on the floor as you'll need to tweak the delay time.
There are a number of different ways to do this either "in-the-box" (i.e. within a computer DAW environment) or outside as I did here. I prefer the "external" approach, mainly because real analog delays usually have a lot more character and distort in funnier more obnoxious ways than their software counterparts. Here I'll detail how I did it in analog synth/stompbox world.
Click on the diagram at right for a breakdown of how I set everything up. First, we ignore the MIDI controller, MIDI>CV and VCA sections and just concentrate on the oscillator/mixer combo and the Poly Chorus (you can use whatever delay you like as long as it has a feedback knob that'll let it go into runaway feedback — analog delays usually sound nicer). I used a low sawtooth wave to feed into the effect. I set the feedback knob on the Poly Chorus all the way up, then turned on the sawtooth wave for a couple of seconds to excite the Poly Chorus feedback. You'll only need a second or two to get the delay going if the feedback is all way up, then you can just shut off whatever sound you're sending in. The mixer isn't really mixing anything at all here, it's just acting as an on/off switch and a volume knob so we don't send too much level into the delay (my modular system has a custom mixer with toggle switches, so all I need to do is just flick 'em on and off real quick).
You can hear what my little "blip" of sawtooth sound used to excite the delay sounds like in the triggertone.mp3. Keep in mind that the specific sound you use isn't very important. Anything relatively low-pitched with a lot of harmonic content will work fine--even snare drum samples.
As long as the feedback knob on the delay is cranked up, you should hear noise. You can futz with the pitch by adjusting the delay time knob. By leaving the time setting knob in different positions for varying amounts of time, different frequencies will "catch" and start feeding back. Take some time to play with this, as there are a lot of variations to be found- if the sound starts getting dull and murky, turn the delay way down, and you'll hear the high harmonics build up again. Check out the feedback_continuous.mp3 file for an example of this. Another thing- different delays have different tones, especially if you have analog, digital and tape delays to play with. Experiment to see what works best!
Now that we've got the noise going, I'll explain how to use a keyboard to turn it on and off so you can play in time...
The inherent problem with trying to "play" feedback like this is that it takes a while before the harmonics build up for optimum sound. So the idea is to get it feeding back nicely in the "background", then use a keyboard to turn the sound on and off. Using my modular, I took the output of the existing feedback loop detailed above, and used a voltage-controlled amplifier (VCA) as a simple keyboard-controlled gate. In other words the sound plugs into the VCA, which doesn't allow it to pass until I press a key, then it's open sesame. I started by plugging a MIDI controller into my MIDI>control voltage converter. The MIDI>CV converter has a pitch CV which would usually tell the oscillators what note to play, but we don't need it here. I simply took the gate out and routed it to the VCA control in; when I press a key on the MIDI controller, it sends +5 volts thus allowing sound to pass through the VCA. I then can play the keyboard in time with music while I'm recording to my DAW, and I can twist the delay time knob in order to get pitch sweeps... or throttle revving. You can hear some examples in thefeedback_triggered.mp3file.
If you don't have a fancy-schmancy modular synthesizer, you can do the VCA gate trick with many noise gates or compressor/gates with a "keyed gate" feature. This is really common- you can find used Behringer rack mount compressors for small change with keyed gating. It's the same idea; you feed the audio signal through it's standard audio I/O, and instead of using control voltages to open and close the gate, you plug a synth with an on/off organ-style patch into the "key" input. This behaves the same way, letting audio through when you hold down a key (I like the the modular synth way better because it's a little more responsive, but I'm sure this depends on the gate used; i've only used cheap ones!).
Have fun revving your engines. I'm sure it's apparent that there's plenty more creative sounds to be made using feedback delay tricks!