Question

I am currently creating an application which signals readiness to other devices using a high frequency sound.

(transmitter): A device will produce a short burst of sound of around 20khz.

(receiver): Another device will be listening for a sound at this frequency at a small distance from the transmitter(10m approx) The device recieves audio data from a microphone

The background noise will be fairly loud, varying from around 0 – 10khz(about human speech range), and would be produced by a small crowd of people.

I need the receiving device to be able to detect the 20khz sound, separated from the noise,

and know the time at which it was received.

Any help with an appropriate algorithm, a library, or even better, code in C or

Objc to detect this high frequency sound would be greatly appreciated.

Answer 1

20 kHz may be pushing it, as (a) most sound cards have low pass (anti aliassing) filters at 18 – 20 kHz and (b) most speakers and microphones tend to have a poor response at 20 kHz. You might want to consider say 15 kHz ?

The actual detection part should be easy – just implement a narrow band pass filter at the tone frequency, rectify the output and low pass filter (e.g. 10 Hz).