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.
In: 678
As someone already mentioned, today’s microcontrollers are “wicked fast”. Yet, they’re not the fastest! Because, you see, they’re actually “general purpose” computers and, as such’ have to do many things that may or may not be related to a particular task (in this case, noise cancellation).
Some “computers” are built specifically to deal with processing fast signals, and these are called Digital Signal Processors (DSPs). These are way faster at their job than normal processors (but not much good at anything else).
Also, FPGAs (or Field-Programmabla Gate Arrays) are nothing more than the very basic building blocks of microcontrollers, except they are not pre-configured in any general purpose functions, but instead are left for the developer to arrange them in the best way to efficiently solve the task at hand. This is more complicated to do, but the end result is MUCH faster than a run-of-the-mill controller.
If there is enough of a market (and hundreds of thousands of headsets should be), then engineers design special-purpose chips FROM SCRATCH that do one thing and one thing only (and nothing else), but in the most effective way. These are called, for obvious reasons, Application-Specific Integrated Circuits or ASICs. Let’s just say that they are fast…
We have a lot of play in our hearing. Speech from someone talking can be significantly out of sync before we notice.
In addition to processing speed something like airpods are probably running machine learning software that is trained on patterns and are predictive rather then reactive.
I don’t think you understand how fast computers are.
Remember how photons aka. light is the fastest thing in the universe? Well, your computer can do around 5 to 10 complete operations between the time the *photons* from the screen reach your retina.
Laptops and desktops can do around 3 billion operations a second. *Small chips powered by button cells* can still go into the millions or tens of millions of operations a second. Your *washer* probably has greater computing power than the computer that sent humans to the moon.
You don’t even need processing to invert the wave-form. Just flip the wires from the microphone to the speaker, and that alone will invert the wave. Then just tune the amplitude to exactly match what’s needed to cancel out the sound. This can be done extremely quickly.
In pro audio I can make a cable to reverse the phase of a signal. I have it in case a mixer doesn’t have a phase button. The mixers phase button is doing the same thing the cable is. Any electrons are much much fater than sound.
No DSP is required. Phase was getting inverted way before computers entered the pitcure.
Is there such a thing as noise-cancelling speakers? If hypothetically one had super loud neighbors could you blast “noise-cancellation” back at them? Somehow I feel like this would definitely not work and maybe would have something to do with waves dispersing or something…
If you listened to a live broadcast of a concert on your headphones while sitting in the front row of that concert, you would theoretically hear the sound before the audience did.
Electricity moves at the speed of light.
>this means the AirPod has 1/34,300 seconds or ~0.03 miliseconds to do these operations to cancel the wave.
Computers (even smaller, cheaper ones) are capable of performing tens of thousands of operations in the span of 0.03ms. That’s how they’re able to work so fast…from the perspective of a modern computer, sound moves very slowly.
Audio signals move throw wires much much faster than the same acoustic energy would move through the air.
This is why, even in small rooms, when you have several sets of speakers that are at difference distances from the front or stage area, you need to actually add audio delay to the speakers that are farther away. The audio will travel faster through the wires to the speakers and get there before the same audio naturally carries from the stage. And I’m talking like….30 feet.
So yeah it’s totally plausible that the audio will travel through the tiny bit of wire from the mic to the speaker before the natural acoustic energy gets there.
The microphone is slightly closer than the speaker driver which gives it just enough of a head start. And yea, computers really are that fast
Latest Answers