I have a device that can transfer measured signal to mobile phone via audio frequency modulation, a nice way for wireless communication just using microphone and without BLE pairing . I am trying to make a B4A app that can realtime demodulate/plot the signal since it is interesting to learn how it works. Any signal processing gurus here have experience on this could share anything? The audio is sampled at 44100Hz and the 300Hz signal is modulated at 19KHz+-1KHz.