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Ask HN: How do browsers isolate internal audio from microphone input?
11–20 of 106 posts
Re: Ask HN: How do browsers isolate internal audio from microphone input?
#12A side effect of echo cancellation. Browser knows what audio it is playing, can correlate that to whatever comes in through the mic, maybe even by outputing inaudible test signals, or by picking wide supported defaults.
This is needed because many people don't use headphones and if you have more than one endpoint with mic and speakers open you will get feedback gallore if you don't do something to suppress it.
Re: Ask HN: How do browsers isolate internal audio from microphone input?
#13The way this works (and I'm obviously taking a high level view here) is by comparing what is being played to what is being captured. There is an inherent latency in between what is called the capture stream (the mic) and the reverse stream (what is being output to the speakers, be it people taking or music or whatever), and by finding this latency and comparing, one can cancel the music from the speech captured. With…
It just seems more logical for the OS to do that, rather than the application. Basically every application that uses microphone input will want to do this, and will want to compensate for all audio output of the device, not just its own. Why does the OS not provide a way to do this?
Re: Ask HN: How do browsers isolate internal audio from microphone input?
#14The technical term that you're looking for is acoustic echo cancellation[1].
It's a fairly common problem in signal processing, and comes up in "simple" devices like telephones too.
[1] https://www.mathworks.com/help/audio/ug/acoustic-echo-cancel...
Re: Ask HN: How do browsers isolate internal audio from microphone input?
#15Since chrome has the data from both sources: the microphone, and the audio stream from YouTube, I imagine you can construct a filter from the impulse response of the YouTube source and then run the microphone through it
Re: Ask HN: How do browsers isolate internal audio from microphone input?
#16It's called Acoustic Echo Cancellation. An implementation is included in WebRTC included in Chrome. A FIR filter (1D convolution) is applied to what the browser knows is coming out of the speakers; and this filter is continually optimized to to cancel out as much as possible of what's coming into the microphone (this is a first approximation, the actual algorithm is more involved).
Re: Ask HN: How do browsers isolate internal audio from microphone input?
#17The way this works (and I'm obviously taking a high level view here) is by comparing what is being played to what is being captured. There is an inherent latency in between what is called the capture stream (the mic) and the reverse stream (what is being output to the speakers, be it people taking or music or whatever), and by finding this latency and comparing, one can cancel the music from the speech captured. With…
It just seems more logical for the OS to do that, rather than the application. Basically every application that uses microphone input will want to do this, and will want to compensate for all audio output of the device, not just its own. Why does the OS not provide a way to do this?
How sure are you that Basically every application wants this? So should there be a flag at the os level for enabling the cancellation? How do you control that flag?
Re: Ask HN: How do browsers isolate internal audio from microphone input?
#18Search for the compilation flag "CHROME_WIDE_ECHO_CANCELLATION" in the Chromium sources, and you will find your answer.
Can't tell you anything else due to NDAs.
Re: Ask HN: How do browsers isolate internal audio from microphone input?
#19The way this works (and I'm obviously taking a high level view here) is by comparing what is being played to what is being captured. There is an inherent latency in between what is called the capture stream (the mic) and the reverse stream (what is being output to the speakers, be it people taking or music or whatever), and by finding this latency and comparing, one can cancel the music from the speech captured. With…
It just seems more logical for the OS to do that, rather than the application. Basically every application that uses microphone input will want to do this, and will want to compensate for all audio output of the device, not just its own. Why does the OS not provide a way to do this?
> Basically every application that uses microphone input will want to do this
The OS doesn't have more information about this than applications and it's not that obvious whether an application wants the OS to fuck around with the audio input it sees. Even in the applications where this might be the obvious default behavior, you're wrong - since most listeners don't use loudspeakers at all, and this is not a problem when they wear headphones. And detecting that (also, is the input a microphone at all?) is not straightforward.
Not all audio applications are phone calls.
Re: Ask HN: How do browsers isolate internal audio from microphone input?
#20The way this works (and I'm obviously taking a high level view here) is by comparing what is being played to what is being captured. There is an inherent latency in between what is called the capture stream (the mic) and the reverse stream (what is being output to the speakers, be it people taking or music or whatever), and by finding this latency and comparing, one can cancel the music from the speech captured. With…
Is there any way to apply this outside the browser? Like, is there a version of this that can be used with Pulseaudio?