# Noise Cancelling [duplicate]

Possible Duplicate:
Does this exist: software for noise cancellation

Is it possible to take advantage of a modern day pc (or laptop) and create a noise-cancelling dev environment? My laptop has good quality speakers & microphone and plenty of excess CPU.

Is this something someone has managed to pull off?

• i'd be willing to wear headphones, but would prefer to not even need to do that Commented Jul 21, 2010 at 4:49
• and yes i'm aware of off-the-shelf noise cancelling headphones - boring! Commented Jul 21, 2010 at 4:49
• Are you looking to write a program to do this, or are you looking for existing tools? Commented Jul 21, 2010 at 4:52
• Would prefer to get existing tools Commented Jul 21, 2010 at 4:54
• I think that for noise cancellation to work, you have to have a the speakers near your ears, and microphones right next to them. Then you just play back the sounds at the same amplitude but inverted.
– Gabe
Commented Jul 21, 2010 at 4:55

This cannot be done for two reasons.

1. It needs to be directional. Sound waves are spherical, and spherical waves without common centers don't overlap nicely. So you can't produce a "localized cancellation field". You can only put something very close to your ear and cancel things aiming inwards, because that's unidirectional.

2. Your microphone and your speakers need to have a known distance between them, and it cannot be off by an appreciable fraction of the wavelength of sound you are trying to cancel.

• Consider the buzz of your air-conditioner. It's emitting, say, 10KHz. (We're talking spherical cows here.)
• Speed of sound is 343 m/s. So you can pack 10K waves into 343 meters. That's 0.0343 meters wavelength = approx 3 cm.
• So your microphone must read the wavelength and create an exact opposite-magnitude wave that lines up with it perfectly.
• That means it needs to know how far its microphone and speaker are from each other (so it can adjust for the wave travel time), and the relative direction.
• If it's off by 3cm = 1/10000 of a second, it constructively interferes, making your A/C louder!
• And if it's not totally on, it doesn't do much but add more noise.

I don't know much about the science of acoustics, but from reading the wikipedia article on Noise-Cancellation, it seems like you would need the speakers to be right next to your ears (i.e. earphones) in order for this to work, so that each ear could get the correct (and distinct) anti-noise pattern.

So, if your goal is to not need to wear earphones, I think you might be out of luck.

You probably can't do this using a computer. To do noise cancelling you need a really short delay in between receiving the signal and getting the speakers to counteract it. The latency introduced by the PC would almost certainly be too much. Existing noise cancelling devices use fast DSP for this.