Uses the audio autput to generate sound pulses and then detects the echo on the microphone. The echo signal can be visulised in a map, Fourier transformed or just as the time-series waveform. Great for investigating/demonstrating acoustics principles. RECORD_AUDIO Permission to use microphone to detect the echo. WRITE_EXTERNAL_STORAGE Permission is so that data can be saved. Features/Specifications: • Sampling frequency 44.1 kHz. • Sampling duration 0.001 s to 5 s. • Single / Continuous