Android Microphone To Pick Up A Specific Tone

Question

Hello I was wondering if using the android tone generator class would it be possible to create a tone in one device and listen for this same tone in another device. If this is possible I do have a few other questions.

Taking backround noise into consideration is it possible to listen for only this specific tone?

Would this process be resource intensive?

Could I use a tone that would be inaudable to the human ear or close to it?

Lastly could I use a tone that could only be heard with a couple of feet from the sending device?

Thanks very much for yer time guys and girls :)

Edit > Thanks For adding the audio processing tag sabastian. Much better discription.

Answer 1

It would be CPU intensive, yes. The way to it is quite simple: you need a permanent recorder which puts the received data into a FFT (fast fourier transform). FFT basically does one thing: splits the audio into a frequency/power-scale. With this "background noise cleaned" result you can check things like "was there a tone with 1000Hz playing for at least 2 seconds" - and act accordingly. There is a reasonable speed FFT implementation here: http://www.badlogicgames.com/wordpress/?p=449 FFT can also be used (actually, IS used) for detection of dualtone dialing (DTMF) - 2 frequencies at same time is much better than just using one (as the error rate drop significantly and you can go to shorter duration for the tone sending/detecting).

"Inaudible" won't be possible, as (a) the speaker can not produce such sounds (b) you are limited in sampling rate - so also limited in both producing and recording such high frequencies.

"couple of feet" will be naturally imposed (not very loud speaker, not very good microphone).

Answer 2

Have a look at this other question: "Android: Need to record mic input". I think you can modify that for your task, then with sound bytes you can have filtering or FFT.

Hope it helps