GanondalfTheWhite t1_j2dipov wrote
Reply to comment by frzx1 in Eli5 How exactly does Noise cancellation work? That too in such small airbuds by Professional-Ad3441
I'm always amazed that it's able to respond so quickly. I'd think the processing time required would introduce more offset than it does.
Implausibilibuddy t1_j2dk2br wrote
It is quick but not instant which is why active noise cancellation works well on low frequencies and not too well for higher.
Low frequency sounds have a wider wavelength (and thus occur over a longer period of time). You can have a little latency between the live and generated sounds and they will still mostly overlap and cancel out. For high frequency sounds there could be several peaks and troughs in the offset gap and they're less likely to line up with the generated sound.
IShouldBeHikingNow t1_j2ewg8x wrote
Which is why they're great an cancelling out the low hum of the airplane but not the shrieking banshee child two seats over?
TheRealAmadeus t1_j2f7f8y wrote
PreCISELY
hgrunt t1_j2ftc1s wrote
It doesn't help that we're particularly sensitive to crying/screaming because it's a sign of distress
frzx1 t1_j2djr04 wrote
There's a lot that goes into noise cancelling, they are not always doing everything in real time. There are specially designed and fully dedicated chips on the sound devices that do just one thing, noise cancelling. They recognize certain sounds and apply the noise cancelling beforehand, thus eliminating that time window. They've been trained on millions of hours of noise and have gotten really good at what they do. Power of data, indeed.
angermouse t1_j2ewgfw wrote
I didn't know noise canceling relied on machine learning. It doesn't need to and the older ones likely did not.
angermouse t1_j2dw1jh wrote
It takes advantage of the fact that light and electrical fields travel about a million times faster than sound (300 million m/s versus 300 m/s). If you think about it, sound is extremely slow. Hearing echoes is a common occurrence and animals like bats even use it for navigation.
noopenusernames t1_j2edsft wrote
It doesn’t have to be perfect to still be effective. Let’s say you have a sound coming in at 150 dB, which is definitely not hearing safe, and the headphones have a delay so they can’t perfectly match up the anti-wave directly over the incoming wave - as long as the anti-wave moves the crests and troughs in the right direction, you create this new wave that’s mostly cancelled out, but you might get some, like 5 or 8 or 3 dB through, which is much safer
The_quest_for_wisdom t1_j2e3wkw wrote
We assume the speed of sound is much faster than it is. Locally it seems almost instantaneous, when it is not.
If you have a large bell like the kind used in a church steeple you can see this disconnect with your own eyes.
If you get more than about an eighth of a mile away you will see the ringing bell move quite a bit out of sync from the sound of the bell ringing that you hear.
It gets even wielder when you consider that the image of the bell being rung is also arriving in your eye AFTER the bell is actually being rung, due to the speed of light. It's just a much shorter delay.
It might be tempting to just hand wave that away and say that the light travels effectively instantaneously, but that thinking with sound is exactly how we ended up here in the first place.
GanondalfTheWhite t1_j2elevv wrote
> thinking with sound is exactly how we ended up here
While everything you said is true, the speed of sound, which, yes, is much slower than light, is still pretty damn fast when we're talking about how much time there is to process something in the time between a soundwave passing from one side of your earbud to the other. Right? Cuz that's what we're talking about. Not how long the sound of something vs. the light of something takes to hit your brain.
Ultimately what we're talking about is that the earbud needs to be able to detect the soundwave, compute its opposite waveform, and emit the counter wave all in the same time that it takes for the soundwave to pass the earbud so that the original wave and the counterwave hit the eardrum at the same time. Right?
So if we assume the earbud is maybe half an inch thick, means it has to do all of that in about 1/27,000th of a second. 0.04 milliseconds.
Even knowing how fast sound travels, that ability to process seems unintuitively quick. That's all I'm saying, it's unintuitive and pretty darn cool.
IsardIceheart t1_j2eb5hh wrote
I'm pretty sure they use pure hardware, no software to do it, because software is too slow.
(This information may be out of date, but this was true not that long ago)
frzx1 t1_j2edyaa wrote
Hardware alone cannot do a lot of stuff that we see today, the true power lies in silicon, and consequently the computation it does. Also, software is far from being 'too slow', I'd even go ahead and say that software at present is far more quicker than hardware.
f4f4f4f4f4f4f4f4 t1_j2ekf2k wrote
Hardware meaning integrated circuits, which are made from silicon...
IsardIceheart t1_j2epxzg wrote
Lmao, yeah this guy is dense.
Also... software is never faster than the hardware it runs on, by definition.
frzx1 t1_j2eknuz wrote
What do you think I'm talking about? CRT monitors?
IsardIceheart t1_j2eg99f wrote
Yeah, okay buddy.
I did some research and it looks like active noise canceling is still done with purely hardware, because software cannot process the sound fast enough.
By purely hardware I mean it is an analog system, not digital.
wbsgrepit t1_j2fc7vq wrote
This is kind of true and kind of false, Software speed is limited by the hardware it runs on — there is certainly software that is fast enough to do this work very well (given the right hardware to run on), however, given the constraints of many noise canceling headphones it is currently much more cost effective to bake that logic into chips especially designed for this work vs using a much more expensive general purpose cpu etc.
IsardIceheart t1_j2fjr4l wrote
Yeah, I guess the point is that general processing is unsuitable for the work, rather than incapable.
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