This is a very cool demo. There are a couple of ways to improve this technique, improve accuracy, reduce power, and improve noise rejection.<p>The biggest wins are in improving the waveform from this one (called "continuous wave" or CW in the radar/sonar literature) to one with more bandwidth. One option is to sweep the frequency continuously (FMCW) or with breaks. Another option is to switch from this continuous noise to pulses of noise, just turning the sound on and off. Pulsing like this increases bandwidth (because the "turning on and off" introduces higher-bandwidth edges) very simply. Modulating the frequency during the pulse helps more, creating a wolf-whistle like "chirp".<p>Doing the signal processing for these alternative waveforms is a little bit trickier than the technique this page uses. It can be done in the time domain with correlation, or in the frequency domain with the the FFT and simple multiplication.
I had read about SoundWave a long time ago and emailed the researches if they were going to do anything with it or if they could open source their code. Unfortunately they told me it was "just a PhD" and that I could re-build it from the paper. I am super super super happy and glad to see that you've gone ahead and implemented it. Thank you so much.
Very cool!<p>However it makes me crazy... I hear that noise clear as a bell and I'm 42. Wikipedia says that human hearing typically goes up to 20kHz. (<a href="http://en.wikipedia.org/wiki/Hearing_range#Humans" rel="nofollow">http://en.wikipedia.org/wiki/Hearing_range#Humans</a>)<p>So maybe you want to go high enough that a much lower % of the population will go bonkers?
Very cool idea, but unexpectedly my girlfriend started screaming and didn't let me keep the sound on for more than a second or two. She said it was a terrible noise and gave her a headache.I didn't know it but it appears she can hear 22 kHz.
wow cool idea. I wonder what could be achievable in terms of precision with different frequencies on seperate speakers and 2 or 3 microphones; a paper(printed) or laser lit (on a surface) keyboard?