audio - Detect frequency from microphone Java -

i make program can transfer data pulses of frequency unsure on how detect if frequency present.

i assume need filter out unneeded frequencies can't seem find on how this.

are there libraries or have build own? there examples of or similar being done?

it looks though you're trying implement modem, , advised @ proven modulation techniques used purpose - qpsk , qam. technique imply in question crude of amplitude modulation - modulating carrier of given frequency bit-stream. heterodyning might place start when demodulating this. using fft yield poor results because of sampling effect of windowing, result in poor bandwidth.

another practical problem face once you've demodulated signal clock recovery. highly probable original bitstream clock asynchronous sample clock @ receiver. in order decode data-stream, need recover sender's clock (that say, relationship between , local clock). phased lock loop usual way of achieving this.

you need work out how detect start of bit-stream - e.g. kind framing.