Waveforms generator to test a Hi Fi system You connect the headphone wire to the AUX input of the Hi Fi. Available waveforms: Sine, Triangle, Ramp-Up, Ramp-Down, Square Wave (duty selectable 10,20,25,30,40,50%). Frequencies range from 16Hz to the maximum possible for the device, selectable in steps of 1,10,100,1000,10000 Hz by pick number. The actual audible frequency depends on your Android device. The app analyzes, capturing the sound with the microphone, showing: Frequency determined by FFT