bob wrote: > I basically want to have one Android device send an audio signal to > several other Androids. It will probably be one frequency. I would prefer > if humans can't hear it. > > Does this sound reasonable? Any frequency suggestions? > I spent a few minutes googling for the frequency response of cell phone speakers and microphones.
I didn't find anything conclusive, although it seems that many can reproduce approximately 100 Hz to 20 kHz through the headphone jack. I would be astounded if the tiny, tinny little speaker could even begin to get close to that. But some references seem to give hope that you can get into the 12-15 kHz range. That might suffice, although many humans (especially younger ones) hear fine in that range. Sample rate on the mic side will affect your ability. The highest-resolution recording modes generally sample at 44.1 kHz or 48 kHz, giving a theoretical top range of half those numbers. (I am suspicious of Nyquist frequency claims for digital reproduction.) So your ultrasonic options are rather limited. Bear in mind that the higher the frequency, the more directional the signal. At the treble frequencies implied by your titular "dog whistle", you'd pretty much have to aim one device straight at the other. Have fun. -- Lew -- You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
