> From: "Pastor Doug Coats" <dcoats at heritagemail.org> > I asked a an engineer a similar question when I was working on setting up a > sound system for a gym. Our concern was canceling out the echoes. His > response was that theoretically you can cancel out sound with the reverse > wave length of the same sound. > In practice you would need one of three things to happen. > > 1. You would need to mic the sound at it's source and place the speakers at > the same location. > > 2. You would need mic the location of the ears and place the speakers at > the same location. > > or > > 3. You would have to have a limitless number of mics to pick up all of the > sound waves bouncing off of all of the surfaces for the speakers to conceal > out the sounds. > > The only one that is somewhat practical is number one. Say if you had an > extremely load air conditioner or something and wanted to cancel out it's > noise. Number two would require some sort of headphone contraption > connected to a battery source and a portable/wearable PC. > > As far a Linux being able to accomplish the first idea I don't know. Active noise cancellation is a bit more involved than what you suggest. As an engineer, yes, the principle of creating null points is the idea, but in practice you are talking about a lot of predictive filtering. Ford Motor had a research group that did quite a bit of work on it, maybe 5-7 years ago -- at least they published a fair amount of work in the Journal of the Audio Engineering Society around that time. As far as Linux being able to do it, it doesn't make a whole ton of sense. A standalone / embedded DSP is much more appropriate, but if you wanted to do it for grins, you would want to look at low latency kernels, like the real-time linux project, since it would play havoc with your cancellation (i.e., make the room noisier, since the adjusting signal would basically be noise if *IT* wasn't cancelled out) if the cancelling algorithm's process got niced by some hoggy process, like Java or something. P -- "To misattribute a quote is unforgivable." -- Anonymous _______________________________________________ TCLUG Mailing List - Minneapolis/St. Paul, Minnesota http://www.mn-linux.org tclug-list at mn-linux.org https://mailman.real-time.com/mailman/listinfo/tclug-list