2 ms·

How fast can it need to be? The output frequency would be below 20kHz so latency of 50us or so, probably too fast for a userland app but I'd expect it to be doa

by taneq 4y ago

How fast can it need to be? The output frequency would be below 20kHz so latency of 50us or so, probably too fast for a userland app but I'd expect it to be doable in a driver or in the OS?

bee_rider 4y ago
I get a similar answer but through a wildly different path: I think you have to detect the sound with a microphone, then come up with the canceling waveform before the sound hits your headphone drivers (as they will be generating the canceling waveform). Given the typical size of headphones, it would be something like 2cm/(34300cm/s) ~ 60us Although, sound travels faster through solids, so might want to be a little quicker. And 2cm thick headphones would be pretty thick.
- shreyshnaccount 4y ago
  wonder if there's some kind of "virtual microphone" like device that let's you hear sounds further away than a mic in the headset. Google fu showed some ultrasonic virtual microphone but idk if it is useful here..
  - bee_rider 4y ago
    Hmm, could be. I don't know much about this. I imagine you want a very good approximation of the soundwave that will hit the ear (so you can cancel it out very accurately). The farther that your 'virtual microphone' is from the ear, I guess the harder it will be to figure out exactly how the sounds it is picking up will combine to hit the ear. I mean, imagine the extreme case -- your 'virtual microphone' is (virtually) sitting in the path of some directed audio beam which won't hit the headphone wearer at all. Now you do the signal processing and generate a signal to cancel out that directed audio beam, which, because the user isn't in the path of it, causes them to hear it!
    - shreyshnaccount 4y ago
      yeah, it would have to be super directional..
- taneq 4y ago
  Interesting! I guess our approaches are linked by the fact that the size of our ears is connected to the wavelengths we want to pick up (or cancel out)… and to the size of headphones. :)
shreyshnaccount 4y ago
it effectively needs to be fatter than the speed of sound. sound needs to hit the mic of the noise cancelling device, its inverse needs to be found before the sound hits your ear drums so it can be played at exactly the same time. all this needs to happen in the time it takes for the sound to travel from the devide to your ears. super fucking fast.

by taneq 4y ago

How fast can it need to be? The output frequency would be below 20kHz so latency of 50us or so, probably too fast for a userland app but I'd expect it to be doable in a driver or in the OS?

bee_rider 4y ago

I get a similar answer but through a wildly different path: I think you have to detect the sound with a microphone, then come up with the canceling waveform before the sound hits your headphone drivers (as they will be generating the canceling waveform). Given the typical size of headphones, it would be something like 2cm/(34300cm/s) ~ 60us Although, sound travels faster through solids, so might want to be a little quicker. And 2cm thick headphones would be pretty thick.

shreyshnaccount 4y ago
wonder if there's some kind of "virtual microphone" like device that let's you hear sounds further away than a mic in the headset. Google fu showed some ultrasonic virtual microphone but idk if it is useful here..
- bee_rider 4y ago
  Hmm, could be. I don't know much about this. I imagine you want a very good approximation of the soundwave that will hit the ear (so you can cancel it out very accurately). The farther that your 'virtual microphone' is from the ear, I guess the harder it will be to figure out exactly how the sounds it is picking up will combine to hit the ear. I mean, imagine the extreme case -- your 'virtual microphone' is (virtually) sitting in the path of some directed audio beam which won't hit the headphone wearer at all. Now you do the signal processing and generate a signal to cancel out that directed audio beam, which, because the user isn't in the path of it, causes them to hear it!
  - shreyshnaccount 4y ago
    yeah, it would have to be super directional..
taneq 4y ago
Interesting! I guess our approaches are linked by the fact that the size of our ears is connected to the wavelengths we want to pick up (or cancel out)… and to the size of headphones. :)

shreyshnaccount 4y ago

it effectively needs to be fatter than the speed of sound. sound needs to hit the mic of the noise cancelling device, its inverse needs to be found before the sound hits your ear drums so it can be played at exactly the same time. all this needs to happen in the time it takes for the sound to travel from the devide to your ears. super fucking fast.