Slashdot Mirror
Software Noise Cancellation?
DangerTenor asks: "As I flew around the world, lusting after my coworker's $300 BOSE Quiet Comfort Noise-cancelling headphones, I looked down at my laptop computer and noticed the built-in microphone. Has anyone written or considered writing software to run noise-cancellation based on the built-in mic?"
It would be great if reality were that cooperative, but unfortunately there is no such thing as a "constant or regular, repetitive sound", unless you're talking a digitally-generated sine wave out of a good speaker.
This become especially noticable with high-pitched sounds (or components of sounds) you are trying to cancel. Suppose for the sake of argument there's a 5,000 Hz sound you are trying to cancel that varies randomly in absolute pitch over the course of a second or two by up to 1%, or +/- 50Hz. (1% is easily detectable with training of any sort, but still a lot of people won't notice it, esp. in a noisy situation like fan noise.) Kick in a fudge factor for the fact that your mic can probably barely "hear" that as it is. If your sound canceller is not instantly reactive, it will "cancel" sound from the past (and it can only react at the speed of sound at best), and you could turn an annoying high pitched sound into an annoying 20-50Hz sound, that for bonus points is phased all over the place with all kinds of fun harmonics. Thanks, but no thanks.
And this assumes some sort of ideal environment. It's actually quite hopeless because each speaker of the laptop, assuming it even has two, will affect both ears, plus the reflections of each speaker, plus the reflections of the noise. Real noise dampers put one damper on each ear, because the interaction between the two would take a very challenging math problem and make it an impossible one.
Oh, and the sounds your speaker is making can't reach the mic, either. (Because the sounds can't be cancelled at both of your ears and the mics... in fact, you'll be lucky to manage cancelling the sound at one ear, let alone three places!)
In short, the laptop noise canceller would be interesting to see what kind of crazy phased noises you could get out of your environment, and could even conceivably be useful in some small degree to someone mining their environment for sound effects (musicians, sound effect artists) as an intriguing filter on the world, but for actual noise cancellation, you might as well just stick your fingers in your ears and hmm loudly.