frzx1 t1_j2djei4 wrote on December 31, 2022 at 1:28 PM

Reply to comment by chipdipmcgillicuddy in Eli5 How exactly does Noise cancellation work? That too in such small airbuds by Professional-Ad3441

In my opinion, bad noise cancelling is worse than no noise cancelling at all. Yes, when the noise cancelling isn't that good and responsive, there are moments of noticeable white noise. But with time, brands have gotten really good at noise cancelling and the manufacturers claiming to have noise cancelling in them do their job well.

chipdipmcgillicuddy t1_j2dksvz wrote on December 31, 2022 at 1:42 PM

So say you have some good ones, when the headphones hear a noise and play the inverse to cancel it, can you hear that at all? Also, is there a delay? If there was a gunshot far enough away where the headphones could manage to cover the volume of the shot, would it be able to cancel it out in real time? I just don’t understand how sound can be cancelled without some sort of other sound that plays to replace/mask it, in which case it’s not cancelling it just lessening it.

frzx1 t1_j2dlnsp wrote on December 31, 2022 at 1:50 PM

No, you can not hear it, and that's because it's not being played into your ear, it's being laid on top of the sound that's coming into the audio device. There is no significant delay in it because there are fast dedicated chips in the sound devices that do a lot of computational work when it comes to sound waves. So, they're not always doing this in real time, sometimes they're predicting the sound before it's even completely addressed by the device. If there was a gunshot, far away, yes, it would mask it to a certain degree. That degree is what makes noise cancelling good or bad. There's a lot of other stuff that's done to facilitate the sound cancelling, one of them being plugging the ear completely so that no sound wave enter into the ear directly; no ear cavity is left unsealed. Watch THIS video and you'll be amazed to see how apparent this entire process is.

chipdipmcgillicuddy t1_j2dn3k0 wrote on December 31, 2022 at 2:03 PM

I thought about it for a few minutes longer and realized this can work because your wearing something right next to your eardrum. Before I was thinking how could sound be cancelled, if I yell at a concert when the band is playing my yell is still there but it’s drowned out, but I guess because the headphones are right next to your ears that must be a big part of why it works.

Techial t1_j2drnu0 wrote on December 31, 2022 at 2:41 PM

Well, sort of. You also have massive "noise-cancellation" systems built on the same principle when big artists perform live concerts. They literally have subwoofers between the stage and the actual sound-producing subwoofers pointing out to the crowd, and these noise cancelling subwoofers play the same bass sounds (albeit a bit delayed to account for travel) but polarity switched. Imagine sound as a wave going up and down, now if you play the exact same wave but flipped, the waves will cancel out eachother.

nipsen t1_j2dn1d3 wrote on December 31, 2022 at 2:02 PM

It's a little bit less magical than what people are suggesting here.. You don't actually hear as well, so to speak, as a microphone. So there's enough time to invert the soundwave and play it back before you start picking up the vibrations that produce sound you hear.

Alternative way to think about it - you delay the incoming sound slightly and then play it back as perfectly out of sync as you can. The question really is the response, and how quickly you can generate the wave accurately.

The trick is that you should be producing a sound-wave that sounds like what is actually heard behind the clogs, for example. And you really don't want to play back a really, really loud sound, or increase the wave too quickly based on some extrapolation, etc. And it's typically not perfect, so you get noise. You can also mask it all and increase response, so to speak by having a noise-floor.

But yeah, if you play back some fairly low volume sound where the noise is not physically noticeable, and you allow for some noise on the bottom here -- an exactly out of sync wave is going to cancel the sound out, in the sense that your ear is not going to vibrate and make you hear sound.