What causes the feedback (a noise increasing in intensity and pitch)?

In summary, the feedback (a noise increasing in intensity and pitch) sometimes heard when people speak through microphones is caused by the unity gain crossover of the full system and the additional feedback delay caused by the speaker. This frequency is usually at the higher end of the audio system's frequency response, resulting in a high-pitched squeal. It can be understood in terms of phase margin or gain margin, similar to analyzing the phase margin of an amplifier with feedback.
  • #1
cepheid
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What causes the feedback (a noise increasing in intensity and pitch) sometimes heard when people speak through microphones? I'm sure I have enough background to understand an explanation, I've just never thought about it before.
 
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  • #2
Think about it in terms of phase margin (or gain margin if you prefer). You're familiar with analyzing the phase margin of an amplifier with feedback? The amplifier in this case is the microphone --> speaker audio amp, and there is additional feedback delay caused by the speaker --> microphone portion.

The frequency of the squeal is determined by the unity gain crossover of the full system, and the lowest frequency where you have a >= +1 gain. That frequency for audio systems is usually at the higher end of the frequency response of the system, hence the high-pitched squeal.
 
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  • #3


The feedback (a noise increasing in intensity and pitch) heard when speaking through microphones is caused by a loop between the microphone and the speaker. When the microphone picks up the sound from the speaker, it amplifies and sends it back to the speaker, creating a continuous loop of sound. This loop causes the noise to increase in intensity and pitch as it gets amplified each time it travels through the loop. This effect is known as acoustic feedback and is more likely to occur in situations where the microphone and speaker are close to each other or when the volume is turned up too high. To prevent this feedback, sound engineers use techniques such as adjusting microphone placement, using directional microphones, and using feedback suppression technology.
 

1. What is feedback?

Feedback is a phenomenon where a sound or signal is picked up and amplified, creating a loop that increases in intensity and pitch.

2. What causes feedback in audio systems?

Feedback in audio systems is primarily caused by the interaction between the microphone and the speakers. When the microphone picks up sound from the speakers, it amplifies and sends it back to the speakers, creating a loop that leads to feedback.

3. What factors can contribute to feedback?

Several factors can contribute to feedback including the distance between the microphone and speakers, the sensitivity of the microphone, and the volume of the speakers. Additionally, the acoustics of the room and the type of microphone and speakers can also play a role.

4. How can feedback be prevented?

To prevent feedback, it is important to adjust the volume levels of the microphone and speakers, as well as the distance between them. Using directional microphones and adjusting the positioning of the speakers can also help reduce the likelihood of feedback. Additionally, using a feedback suppressor or equalizer can also help prevent feedback in audio systems.

5. Can feedback be beneficial in certain situations?

While feedback is generally considered undesirable, it can be used creatively in certain situations, such as for special sound effects or in certain types of music performances. However, in most cases, efforts should be made to prevent feedback as it can be disruptive and unpleasant for listeners.

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