Sometimes when you’re using a headset or performing on stage, the microphone may cause the speakers to produce a high-pitched screeching sound. So what exactly is the noise and how do we prevent it?
Here’s a short and concise answer to that question:
The high pitched screeching sound is called “feedback”. It happens when the microphone volume or speaker volume is too loud. The sound produced by the speakers is being fed back into the microphone, getting amplified, and being fed into the microphone again and again. To prevent it try increasing the distance between the microphone and speakers, or turn the gain/volume down.
Now let’s look at audio feedback in more detail!
What is audio feedback?
Audio feedback, sometimes called acoustic feedback, Larsen Effect or simply “feedback”, is the high-pitched screeching sound produced in sound systems. The sound can also be described as a squealing or ringing noise.
This positive feedback is caused by a “looped signal”. When we speak into the microphone, if the volume is too high, the audio being played back by the speakers will feed into the microphone again and again. This will create a continuous loop where the audio signal is amplified by a huge amount in a very short timespan.
Although most of the time we tend to avoid audio feedback, sometimes musicians especially guitarists will use controlled audio feedback to add musical character to their songs. When you see a guitarist holding the electric guitar very close to an amp to cause a high-pitched screech, the guitarist is causing “feedback” intentionally.
Why does audio feedback occur?
In a typical audio system, there are 3 basic components:
- Microphone
- Amplifier
- Speaker
Although in real life there are many more components involved, we’ll only look at these 3 parts for the sake of simplicity of demonstrating how audio feedback works.
Basically, when we speak into the microphone, the microphone picks up the audio signal and sends it to the amplifier. Because the microphone signal is very small, the amplifier boosts the signal so that when it sends the signal to the speaker, we are able to hear the sound clearly.
Now imagine we speak into the microphone, the amplifier amplifies the signal, the speaker plays it back in a much higher volume and then the microphone picks up the louder signal. What would happen now? Well, that signal will get amplified again, gets played back in a higher volume through the speakers, and gets picked up by the microphone again. Round and round it goes.
This is essentially why audio feedback occurs. The microphone isn’t supposed to pick up the signal played back from the speakers in a properly set up audio system. However, in real life situations, it may occur more often than you think. Maybe the microphone is being held too close to the speakers or the speaker volume is turned up too high. Whatever the reason, the underlying cause of audio feedback is that the microphone is picking up the signal from the speaker that is connected to itself.
How to eliminate audio feedback?
Eliminating audio feedback has been a constant battle in the audio industry. In some cases, it is relatively simple to solve, but for some venues or equipment, it takes professionals to control it.
Here are the common ways of eliminating audio feedback:
- Use a directional microphone. These microphones have a narrower area for picking up sounds. This means that if the microphone isn’t directly pointing at the speakers, you’ll lower the risk of getting audio feedback.
- Don’t point the microphone towards the speakers. Stand behind or beside the speakers rather than in front. This will help to prevent audio playback from being fed into the microphone.
- Turn off the microphone when you’re not using it can help to prevent sounds from speakers accidentally leaking into the microphone when not in use.
- Turn down the speaker output. This way, the microphone won’t pick up the audio from the speaker. However, if you turn the speaker down, you may need to speak closer to the microphone.
- Use technology that detects and eliminates feedback loops. A noise gate is a common way to reduce audio feedback, as it shuts off the audio signal automatically when the volume gets too high.
- Use equalization on the mixer. Lowering the frequencies that are causing issues can help to improve the overall sound. This requires experienced sound engineers.
- Do not aim the speakers directly towards walls or reflective surfaces. This is to prevent the audio from reflecting and causing the microphone to pick up the signal, even if the microphone isn’t directly pointing at the speakers.
- Replace microphones with direct input for instruments. You can find pickups for most instruments nowadays, reducing the risk of creating a feedback loop on stage.
- Use in-ear monitors on stage instead of speakers. Because in-ear monitors produce audio that is very quiet, there is little to no chance for the microphone to pick up the sound.
There are cases where the audio feedback is faint and only occurs on certain words when you speak into the microphone. It may be an unpleasant tone in the sound or a very faint ringing sound in the background. This means that audio feedback is still present, and the problem should be fixed if possible.
Why is audio feedback high-pitched?
You may notice that most audio feedback is very high-pitched. But why is that? If an audio signal is amplified, it should retain the characteristics of the sound instead of just producing a squeal, right?
Well, the truth is that microphones, speakers, and room acoustics in the real world aren’t perfect. The equipment we use may work better for some frequencies over the others.
For example, microphones and speakers generally pick up and amplify mid to high frequencies better. So in the continuous loop of audio feedback, high frequencies are amplified much more each time around.
The sound starts at fairly low volume and low pitched. But after several loops, the high-pitched sound will dwarf the lower-pitched frequencies in terms of volume. Therefore resulting in a very high-pitched screech that we hear in an audio feedback scenario.
With that said, depending on the venue and situation, audio feedback may not always be high-pitched. In fact, technically it can occur in any frequency. Typically, audio feedback will occur at the resonant frequency of the room, equipment, microphone, or instrument.
