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
Won’t read the replies but I’ll add some little fact:
Audio is highly digital these days, meaning what the other part hears ain’t nothing like a 1×1 voice connection, and yes the byproduct of noise cancellation tech such as mixing and stabilizing multiple microphone sources and applying other hardware/software optimizations such as compression so fast and with such efficiency it happens in what gives us the impression of a real time conversation. Kinda like why phones come with multiple cameras instead of a single one, they’re all working in tandem to construct the illusion of a great camera.
This technology is being expanded for video, in initiatives such as Google’s Starline https://blog.google/technology/research/project-starline/ where again, SEVERAL components are working in amazing speed to give the illusion of real time talk, by emulating what we perceive as real time.
Most speaker phones just cut off the microphone when the incoming sound signal crosses some threshold of volume so you don’t get feedback. It is a simple: “if the audio is loud enough that the mic would pick it up, then turn off (or turn way down) the mic”
This can super annoying when someone on a speaker phone is talking and another participant in the call reacts audibly or has background noise loud enough to be heard on their headset mic because every little “hmm” or “yeah” or dog bark cuts off the first person completely. I have a regular call with guy who like to use a speaker phone and a guy who interrupts everyone and I have to tell the first guy that the Interrupter isn’t going to stop interrupting so he’s got to put on a headset if he wants to be heard.
They use software which cancels the speaker noise from the microphone. Many also use input from a rear microphone to cancel ambient noise as well.
Sometimes it doesn’t work perfectly, and due to the half-second or so of lag in digital telephony, you can sometimes hear yourself speaking a half-second later from the other end.
On the whole it works pretty well, though. People have been improving it for about twenty years.
Basically, there are two microphones on most phones one of which is used for noise cancellation. They compare both audio signals from the speaker output as well as from the microphone and subtract those signals. Hence leaving the required signal to be transmitted.
The phone uses 2 or more microphones to determine where in 3D space your voice is coming from in a form of triangulation, by determining how long the different microphones take to pickup the same sounds.
Using smart people algorithms it identifies what sounds are unwanted noise and what sounds are important in a call, and the unwanted noise is cancelled out by inverting the signal.
Inverting a signal in an easy to understand way, a signal is made of sound waves
sound waves are made of alternating periods of compression and refraction of air, or kinda simplified as squeezing and stretching the air to create sound.
If you have sound at the same power. But an exact opposite phase. The two waves will combine. This means the sound will be compressed at the exact opposite amount that it is stretched. And this cancels out sound, or comes very very close to doing so.
So we use two or microphones to determine what is your voice and what is noise. Then it inverts the noise signal and adds it to your call, which cancels out the noise, because it’s not inverting your voice, the anti noise wave doesn’t really effect your voice in a meaningful way.
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