Infinite Sustain Through Controlled Acoustic Feedback

If you’re an electric guitar player, especially a lead guitarist, you probably already know about this.  Lead guitarists often use screaming, positive feedback to make sounds and musical tones that sustain indefinitely.  This property can be used to great musical effect.  The problem is how to control the feedback so that the effect is musical, instead of letting it run wild, squealing like a banshee and creating an objectionable ruckus.  Anybody that has ever spent time in a guitar store on a Saturday morning will be painfully aware of how objectionable out-of-control feedback can be.

In the hands of the masters, the effect produced by acoustic feedback can be highly emotive and magical.  Here are some clips of guitarists using feedback in musically interesting ways (certainly worth checking out): – removed due to copyright claim (by a dead guitarist??)

So how do you do it?  Clearly, each of the guitarists (Jimi Hendrix, Tom Scholz and Joe Satriani) in the videos had different equipment, made in different eras, yet each one produced musically controllable feedback.  What’s the secret?  What do you need to produce good feedback and how do you tame it (or at least wrangle it)?  In this post, I’ll share with you what I have learned over the past several decades of messing around with feedback.  It might not be all there is to know, but it is stuff I have stumbled upon that you might find useful too.

Basically, all you need is a guitar amp, lots of gain and an electric guitar.  To get a great feedback tone, you usually need some distortion.  A good weapon of choice for creating enough gain and distortion is a Boss MT-2 pedal (more on why below).  Oh and you’re going to need to have tolerant neighbours or some serious sound proofing.

How much gain are you going to need?  Ideally, you want to push your rig just over the edge, to the point where feedback begins, but not so much that you are unable to control it at all.  It’s worth fine tuning this.  You should be able to start and stop the feedback just by facing toward and away from the amplifier’s speaker.  In line with just-in-time manufacturing parlance, I call this gain setting “just too much”.

Having found the “bite point”, there are better ways to control the feedback available, but it’s something of a dark, alchemical art.  You’re going to have to do a lot of experimenting to get it to work for you.

One of the most useful things you can do is make sure you have a guitar that is fitted with potted humbucking pickups.  Potting involves dipping the pickup’s coils in hot wax and is best left to the professionals.  After-market, “boutique” pickups are usually potted anyway, but ask if you are unsure.  Humbucking is a useful characteristic for a couple of reasons.  Firstly, humbuckers are sensitive and have a relatively high output, which is desirable, they suppress mains hum and they usually have a frequency response peak in the mid range, due to the interaction of the coil inductance, resistance and capacitance.  Because you are going to be using a lot of gain, it can mean that hanging the pickup off two screws with tensioning springs alone to keep everything in place (as is traditional) might result in some unwanted noises, when the pickup rattles and moves about.  Some guitarists remedy this by wedging some medium density foam around the pickup to stabilise it in its body cavity.  I saw a video of Joe Satriani’s guitar tech doing precisely this on YouTube, around the time of the Super Colossal tour.

The next useful thing to do is to tailor your frequency response.  This is a compromise, because you will want a reasonably good tone when you are playing notes and chords, but if you establish a good mid frequency boost (+12 or 15dB at 500Hz to 1kHz – say 800Hz for starters), it can help make feedback easier to achieve and control.  I don’t know if it’s the phase or amplitude response of the filter that seems to be the beneficial element, but in my experience, a mid range boost encourages the lower musical frequencies to feedback first, in preference to higher ones, while eliminating the effect of low, rumbling tones and bass (which just sounds messy).  With the mid range boost in place, you can sometimes stop one feedback note and immediately get a higher one, usually a fifth above the first.  That’s magical, when it happens.

Besides having bags of gain, the EQ section of the Boss MT-2 has a parametrically tuneable mid range boost, which is why it’s a good choice (I told you I would explain why).  You get a great mid boost that you can tune anywhere between 200Hz and 5kHz, along with plenty of EQ gain.  A carefully controlled, stopped wah-wah pedal is also a good tool, because you get a nice mid boost and you can move its sweet spot minutely with your foot, to tune the feedback.  I use and recommend a Jim Dunlop Crybaby 535Q, because it has a gain boost and you can make the mid range pass band sharp or narrow.

I don’t know if this always is true, but a single speaker amp tends to give you more control over your feedback, but fewer musical notes that actually will feedback satisfactorily, whereas having more speakers in your amp’s speaker cabinet seems to give a variety of note and tone options, depending on where you stand, but less control.  Placing chalk marks on the floor where you encounter interesting feedback, when you stand there, is a good idea.  I don’t mean the feedback that happens when you just stand around holding the guitar; I mean the feedback you get when you actually fret some notes or hold a chord.  If you have enough gain, you might not even need to pick the notes, just hold them.

My compromise is to run a stereo rig, consisting of two low-wattage, single-speaker, combo amps.  That way, the differences between the two amps tends to encourage different notes to feedback, but because each amp has a single speaker, I can move closer to one or the other to influence which one I get.  It’s not an exact science, but it feels more controllable to me.

If you are playing live with a PA system, you definitely don’t want to induce feedback through the PA speakers or the floor monitors; you want it exclusively from your guitar amp.  In my limited experience of big PA systems in large halls, you get precious little control over the feedback you get through the PA and monitoring and if you can’t control it, you can’t make it musical.  The guitar amp is where you want to create the tones and notes.  The PA is just to make it louder, in a faithful way.  If the PA or monitors are feeding back, independently of the guitar amp, you need less gain in the PA and/or monitor mix.

Having encouraged you all to turn things up to “just too much” and asked you to play around with feedback, please don’t forget the hearing protection.  Use in-ear noise filters.  There are guitarists who are as deaf as posts because of the continual use of high volumes and feedback.  Ted Nugent and Pete Townsend spring to mind.  The damage is permanent and it creeps up on you faster than you think.  To my way of thinking, there is nothing more tragic than a stone deaf musician.  They’re like blind painters.

You can get lots of good, musical feedback at listenable volumes by using low wattage (<15W) amps and lots of gain.  The goal is low sound pressure levels (SPL), but high gain.  Another approach is a high gain valve/tube amp with Scholz Power Soak, Marshal Power Brake or THD Hot Plate attenuator, or else an amp that lets you turn down the power output (e.g. a Mesa Boogie Mark V or a Blackstar HT-5 or HT-5S – you get the picture).

You should also warn your audience about the high volume levels needed to generate feedback, if you find you need this, or you may be guilty of moral hazard.  It’s not cool to damage the hearing of your fans and you should offer them an informed choice.  It would be super cool if bands offered in-ear noise filters for those fans that wish to hear your music for decades to come, along with the T-shirts and CDs available at the merchandising booth.

Having made it possible to get your feedback on demand, you can control the note of the feedback with a tremolo or by bending the strings.  In the clips above, Joe Satriani does both.  This is where the feedback can be used to create musically interesting effects.  A little vibrato here and a frequency swoop there and you are really cooking!

Don’t forget that you have a volume knob on the guitar.  Use that to control when the feedback and sustain happens and when your guitar is silent.  It’s a good discipline anyway, but more so when your rig is turned up to “patent pending” (to quote Billy Gibbons).

Other ways to get the sustained feedback effect include the Fernandes Sustainer or Sustainiac (mounted in your guitar instead of a neck pickup) or with an E-Bow held in your right hand.  The Boss DF-1 or DF-2 pedals also provide a way to make a feedback effect, but for my money, none of these is as satisfying in use or as free form as using ordinary acoustic feedback.

Happy feedbacking!


About tropicaltheartist

You can find out more about me here: There aren’t many people that exist in that conjunction of art, design, science and engineering, but this is where I live. I am an artist, a musician, a designer, a creator, a scientist, a technologist, an innovator and an engineer and I have a genuine, deep passion for each field. Most importantly, I am able to see the connections and similarities between each field of intellectual endeavour and apply the lessons I learn in one discipline to my other disciplines. To me, they are all part of the same continuum of creativity. I write about what I know, through my blogs, in the hope that something I write will resonate with a reader and help them enjoy their own creative life more fully. I am, in summary, a highly creative individual, but with the ability to get things done efficiently. Not all of these skills are valued by the world at large, but I am who I am and this is me. The opinions stated here are my own and not necessarily the opinion or position of my employer.
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