What is audio feedback?

At its core, audio feedback occurs when the playback of an audio signal is loud enough to be picked back up by an input source. In simpler terms, a feedback loop happens when the output of a speaker is so loud that a sound source like a microphone picks it up again.

The speaker will then try to recreate its own output, resulting in the speaker playing back the capture of its own output, resulting in the awful screeching noise we all know and hate.

This can be a result of the output of the speaker being too loud, the input gain of the microphone being too high, or the microphone and speaker being too close together. A lot of different elements can cause this, and depending on the space you’re in, it may not always be easy to fix, but there are a lot of ways to correct it if you have the right approach.

9 tips for preventing audio feedback

1. Watch your levels

The first port of call is always the level of volume between speakers and microphones. In the context of live music, is the front-of-house PA system too loud and the mics are picking that up? Or is the input gain of an on-stage mic too high?

If it’s an issue while recording, is the monitoring signal coming out of headphones or speakers and feeding back into a mic? Identify the root of the problem by looking at the channel causing feedback on your mixer or interface.

For anything that should be silent but isn’t, it will be the mic that’s causing the issue. Try to lower its input gain and that should fix it. If it’s all of the channels, or multiple mics near each other, the problem is the speaker output volume.

2. Mic and speaker placement

If it isn’t volume that’s the problem, it’ll be positioning and polar patterns causing the issue. What polar pattern is the microphone that’s causing the feedback? How close is it to the speaker? In smaller venues and compact home studios, feedback like this can be easy to encounter, and it’ll take some clever manipulation of space and audio to fix the problem.

Omnidirectional microphones cause feedback in tight spaces for obvious reasons, and cardioid mics might have too wide a pickup pattern for the space they’re in and pick up speaker signals from the sides. Watch for figure-eight polar patterns, too; their strong rear pickup could be grabbing signal from an angle you haven’t thought about.

Make sure your mics aren’t pointing towards any speakers that could be causing feedback, and if you’re sure they’re properly spaced and directed, it may be worth considering using supercardioid or hypercardioid mics to narrow this field and let you get more out of your space.

3. Look at your monitoring

Whether you’re in a studio control room recording vocals or running sound in a venue, monitoring signals can get picked up, too. As much as we all love blasting a mix over midfield monitors in the studio to impress the band we’re working with, if you have mics set up in the control room, it might not be the best idea.

Monitor speaker placement is key both in studios and live venues. Investing in a multi-channel headphone amp like the SubZero HPA800 for the studio will also help this.

In the case of live sound, on-stage monitor wedges are another common source of feedback, so picking up a wireless in-ear monitoring system like the Sennheiser XSW IEM SET will help prevent that.

4. Signal flow and gain staging

Think of what else in your space transmits or picks up audible signals that could be interfering with your sound. If it’s not a mic and it’s not your main speakers, think smaller.

Guitar cab speakers can be another source of feedback, as can guitar pickups, since they can be somewhat microphonic and capture other sounds around them. Even electro-acoustic guitar pickups could be at fault, believe it or not!

There’s a reason brands like Martin make guitar soundhole covers to help prevent this. Proper gain settings for every sound source and playback in your space is key, be mindful of what’s playing back where, and how loud it’s doing so.

5. Feedback suppressors

Sometimes the only solution is the most obvious. Feedback suppressors are a key part of most live sound setups rather than a backup for when nothing else will correct the problem. These are a great failsafe and most live sound engineers will try to have one of these for outboard processing.

Feedback suppressors act as extremely narrow notch filters, like EQ that are fixed to very thin bandwidths, so they don’t change any other frequencies within a signal. Some will automatically detect feedback, and some will need to be set manually instead.

Some engineers will use a graphic EQ to fill this function in a pinch too, or as a preventative measure, but given their affordability and usefulness, a feedback suppressor is a worthwhile investment in most cases.

We recommend the dbx AFS2 for its automatic detection, live and fixed modes, and dual-channel architecture that can be applied to your mixer’s stereo output.

6. Acoustic treatment

Acoustic treatment is far more complex than just slapping some foam panels on the walls, as our guide to acoustic treatment shows.

Feedback can be caused by a buildup of specific frequencies in the room due to the typical behaviour of sound in enclosed spaces. Standing waves exaggerating certain frequencies, particularly lower frequencies can build up in unlikely places and cause feedback.

Plus, things like baffles and enclosures used to isolate microphones while recording or live-miking certain sources can help keep mics that you can’t otherwise isolate out of the way of speakers. This will also reduce the effects of reverb that can also create buildups of specific frequencies.

7. Use EQ

So, we’ve talked about automatic feedback suppression systems and how they notch out narrow frequency bands to prevent buildup in problematic areas. But graphic EQ, the live engineer’s stalwart, is another great way of doing this manually.

Especially if you don’t have a feedback suppressor to hand, monitoring your signal path with a spectrum analyser on a digital mixer or your laptop to find any frequency buildups and gently dipping them with a graphic EQ is an excellent preventative measure.

In the studio, if your space isn’t acoustically treated or still has some issues you haven’t had the opportunity to fix yet, you can do this with plugins or graphic EQ too, whatever you have to hand!

This can be especially useful if you’re doing a more live-style recording session with a band where things can suddenly build up in a crowded live room.

8. Time alignment

Time alignment helps to keep speakers in an audio system firing at the same time. For studios with multiple monitor pairs, surround or Atmos setups, or talkback speakers, you want these to fire at the same time – as delays in signal might mean that something gets captured by a mic when you don’t want it to.

The same goes for live sound, perhaps even more critically. You want front-of-house PA, floor monitors, fill-in speakers, and subwoofers to feel synchronised because it’ll sound terrible for both the crowd and the performers otherwise. Making sure the sound arrives where and when it’s supposed to by adding delays is key to setting up a PA system in any venue.

Without doing so, the same issues caused by untreated spaces can crop up easily, standing waves and phase cancellation can cut information out and create an excess of frequencies. Getting this right is perhaps more important and achievable for live venues than acoustic treatment in terms of impact on the quality of sound the audience hears.

9. Be vigilant

Even when things are going smoothly, engineers need to keep their ears – and eyes – open for the potential of a sudden issue cropping up.

It’s important to monitor channels, frequencies, and changes in songs, so you may receive signs of upcoming feedback before it happens.

For example, if a vocalist steps too far forward in a smaller venue, the proximity of the microphones to the front-of-house PA system will cause feedback.

You may get sudden, short-lived squeals of feedback before it gets particularly bad, so keep an eye out for what’s happening on stage and your monitoring systems, audio interface, or mixer so you can nip a problem in the bud.

What to do when audio feedback occurs

What to do when feedback occurs depends somewhat on your circumstances and the tools you have to hand. However, the best course of action in the studio is to cut or mute the channel causing feedback. Then, you can see if your recorded sound is affected and try to root out the cause.

Reposition speakers, adjust the gain on mics, turn down speaker output volumes, swap mics for something with a different polar pattern or more headroom, whatever makes sense to the cause.

Live sound can be tougher because the last thing you want to do is cut a mic and break the flow of a performance. The best course of action is to tweak your graphic EQ to cut the offending frequency band. Check where your performers are on the stage, too.

If somebody gets too close to the PA system, you can talk to them over their in-ears and make sure they stay a little further back on the stage where possible.

FAQs

What is an example of audio feedback?

An example of audio feedback is the high-pitched screeching sound often heard when a microphone picks up sound from nearby speakers. This occurs when the microphone and speakers create a feedback loop, amplifying and re-amplifying sound.

Why am I getting audio feedback?

You are getting audio feedback because sound from speakers is being captured by a microphone, creating a continuous loop of amplified sound. This often happens when the microphone and speakers are too close or the volume is too high.

How do I get rid of audio feedback?

To get rid of audio feedback, reposition the microphone away from the speakers and lower the volume. You can also use directional microphones and feedback suppressors to help prevent the feedback loop from occurring.

Final thoughts

Audio feedback can be a pervasive problem in audio, but there are a lot of ways to deal with it, identify it, and prevent it before it happens. Hopefully, this guide has helped you feel better about that awful screeching so that the next time it comes up you can fix it quickly and efficiently.

Remember to think about mic and speaker positioning first and foremost, and be ready to respond quickly, and you won’t have to worry about feedback again!

Want to learn more? Check out some more of our live sound guides:

A Guide to Stage Lighting Design and Putting on a Stellar Show

Condenser vs. Dynamic Mics – Which One Do I Need?

The 9 Best PA Speakers for Bands and Solo Performers