how do microphones in a phone not pick up any audio that the speakers put out? if I put a call on speaker mode, how do people on the other end not hear themselves?
In: Technology
I hear myself all the time when my friends with Iphones talk to me on speaker it’s fucking annoying because there’s at least half a second delay and suddenly i’m talking to myself
The microphone is connected out of phase from the speaker, creating a phenomenon known as phase cancellation, in which two identical but inverted waveforms summed together will “cancel the other out”
Have you never heard yourself while on the phone? It happens (used to happen more often) and it’s really annoying.
The first thing a microphone will be connected to is a filter and then an amplifier. The filter is mostly to get rid of things outside of hearing range. Next it goes to the amplifier. The amplifier will have a built in common-mode rejection. This means that a signal on the input that is matching another signal will get snubbed out, while signals unique to the input will be amplified. Typically the common-mode rejection ratio is around 100 dB, so the sound of the speaker on your phone ends up being about 1/1000 as loud as your voice.
They do pick up the audio. But the phone “knows” exactly what electrical signal it is outputting to the speakers create the audio; even with a simple electrical circuit, you can subtract that same signal from what is being output output by the microphone and transmitted over the phone line. That will cancel out most of the noise that was produced by the speakers and hopefully prevent the feedback you normally get with a microphone closer to a speaker.
It’s why if people are talking over each other on the phone you tend to get dropped audio and it just becomes garbled instead of it being very noisy.
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