So I understand the basic principles behind noise cancellation. You essentially use a microphone to record incoming sound waves and create an inverse wave that destructively interferes with the initial wave, thus, cancelling it out. But I don’t understand, practically, how this is done.
Let’s assume the sound wave makes contact with the microphone in the AirPod, which analyses the wave and shoots out an inverse wave, but by that point – the initial sound wave would surely have already reached my ears. The AirPod basically needs to cancel the sound wave before it moves roughly a centimetre or it’s too late.
The speed of sound (in a standard environment like air) is 343 meters per second or 34,300 centimetres per second; this means the AirPod has 1/34,300 seconds or ~0.03 miliseconds to do these operations to cancel the wave. That just seems absurd to me for such a tiny chip in the bloody AirPod.
Someone fix my confusion please.
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One way to quickly process the signal is to do an FFT, converting a time domain signal into a frequency domain representation of the signal.
The frequency domain of a consistent signal is pretty much static, meaning you don’t need to act that fast on time domain to be able to predict and generate the counter signal, you can pretty much just generate it constantly and it always work.
Of course noises have changing frequency domain characteristics, so the analysis is constantly being done and the anti-noise signal is constantly being generated using the latest analysis results.
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