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
As someone who works in a call center, a lot of speakers do pick up their own audio on speakerphone, and the person DOES hear themselves. And we hate it.
This has probably been said but I’m too lazy to scroll through the comments. On an iPhone, when you’re listening in the earpiece, there’s a microphone enabled on the bottom of the phone by your mouth (and bottom speaker). If you enable speaker mode, that bottom mic disables and it enables a mic that’s built into the earpiece so it doesn’t hear the speaker blasting right next to it
Electronic engineer here
Sound’s system in phones has something called “negative feedback loop”
which basically means that it subtracts the output sound from the inputs sound.
here is what it does in a function form
(person voice + phone voice) – **(phone voice from feedback loop)** = person voice
the bold **phone voice** is the signal fed through by the negative feedback loop.
Um we do? Every time all I hear is the echo of my annoying voice
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One very important point – conferencing software never feeds the sound from your microphone back to your speakers. They feed that sound to everyone else, but never to you. This means you can’t get the short-loop feedback howl that is really easy to get in a PA. But you can get the long-loop warble from a loop that goes into your mic, out of someone else’s speakers, into their mic, back to your speakers, and to your mic.
Another thing they do is detect when you are speaking, and adjust the speaker volume down and the mic volume up, then restore the speaker volume and cut the mic once you stop. It doesn’t make for a good result, but it works.
You can also use a ‘comb filter’. Carve regular notches our of the speaker sound, so that a graph of the frequency response looks like a comb. Then filter the frequencies that remain in the speaker output, from the microphone, with a ‘complementary’ filter. The sound you get from such a setup is – well, ugly – but at least you can get rid of the worst echo.
The correct answer is:
Acoustic Echo Cancellation or AEC.
The phone has 1 “channel” of AEC. This is the technology which “cancels out” the audio from the speaker.
Not being the expert but I do believe it may be a form of phase cancellation that happen in between the mic and speaker so that the mic can pick up the sound but will invert them and cancel them out.
The mics do record it. But then it depends on the software, as some do cancel it or ignore it. Where the hardware is placed also affects.
Have a voice call in a game while playing both without headset, just speakers, and you will probably hear that feedback with a second of delay or so.
They do, and it is very difficult to mitigate.
The first step is to isolate the speaker and the microphone from the chassis, as sound is a vibration and the chassis will transmit it better than air. Ths is mechanical engineers job, and it is not easy, esp. on a cramped cell phone.
The next step is to use specific microphones that are directional, and will only pickup sound from a very near source.
Then there is active noise cancellation, where a secondary (or more) microphone records the ambient noise to “substract”it from the one coming from the primary microphone. This is done by software.
Finally, there are various filters, both software and hardware, to eliminate unwanted noise, like echo and larsen. some are integrated in chips, others need to be coded. People often use both.
TL;DR: the microphone picks this up, but phones are made to remove it.
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