Guitar Feedback “Modeling” with Samplers

Guitar Feedback "Modeling" with Samplers

Add an extra dimension to keyboard samplers by emulating "guitar feedback" effects

by Craig Anderton

One of the great aspects about guitar is feedback, but how can you possibly translate that to a keyboard sampler? Here are some techniques that come pretty close, and add another dimension of expressiveness to keyboards. Note that it will really help to have an E-Bow, but depending on how facile you are with creating feedback, this may or may not be necessary.

SEPARATING THE ELEMENTS

There are four guitar feedback elements:

• Attack
• Sustain/decay prior to the onset of feedback
• Initial body resonance feedback
• Body feedback + harmonic feedback (that “whine” that appears at the end of a sustained chord)

The problem with sampling these is that different notes go into feedback at different times, and the character of the feedback is different. I feel a keyboard player would want a bit more note-to-note consistency, so I sample each element individually, then mix them together into a single note using a DAW.

THE SETUP

Of course for feedback, you need to mic an amp. Start recording, and hit a power chord. After getting a good attack, let the note decay without feeding back. Then, bring the guitar in toward the amp and touch the headstock to the amp. Doing this creates noise and thunks until the guitar is firmly pressed against the amp, but using a DAW makes it easy to cut out the sample’s bad parts.

Once the guitar goes into body feedback, let it sustain for a while. Then to get the harmonic feedback, I drive one of the chord’s strings with an E-Bow to make the process easy. There will be some discontinuity while switching on the E-Bow and waiting for it to feed back, but that’s not an issue. Capture about 10 seconds of sustained E-Bow harmonics, then stop recording.

CUTTING UP

I like to get about a 10-12 second sample for each note, and loop the final harmonic feedback. I typically end up with a raw sample that’s about 2 or 3 minutes long, so it‘s chopping time (Fig. 1).

Fig. 1: The three elements for a guitar feedback sample, as described next. These eventually get mixed down to a single audio clip, with the end looped using either a digital audio editor or within a sampler.

Isolate the best attack along with its natural decay (about 4 seconds); there’s your first track. Then chop out the best 6 or so seconds of the body feedback for the second track. Then cut about 4 seconds of harmonic feedback—there’s another track.

Next, add crossfades among the various sections to create a single, unified note. Because a guitar’s sound is so rich, crossfaded sections sounded just like part of the sound’s natural evolution.

Now all that’s left is to loop the end. Your DAW probably won’t be able to do that, but you can do the looping in a sampler like Kontakt or MachFive, or a digital audio editor like Steinberg Wavelab or Sony Sound Forge.

THE COUP DE GRÂCE

To provide some control over the feedback sound, I cheat: within the sampler, I layer a sine wave tuned a couple of octaves, or an octave or two and a fifth, above the fundamental (the optimum choice depends on the note, so I choose different notes for different chords, just so that the sounds don’t have too much “sameness”). The sine wave is modulated by three sources:

• An amplitude envelope with a really looooog attack, so that even if the player gets into the looped section, there will still be something evolving and changing.
• Low amplitude vibrato at “finger vibrato” speed.
• Modulation wheel controlling amplitude, so the player can bring in the sine wave “feedback” at any time.

Granted, no keyboard sampler will replace a guitar...but you can still have a lot of fun trying, and even come up with effects that you can’t get with a “real” guitar. Need proof? Check out the resulting sound in the music video “

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 Craig Anderton is Editorial Director of Harmony Central. He has played on, mixed, or produced over 20 major label releases (as well as mastered over a hundred tracks for various musicians), and written over a thousand articles for magazines like Guitar Player, Keyboard, Sound on Sound (UK), and Sound + Recording (Germany). He has also lectured on technology and the arts in 38 states, 10 countries, and three languages.