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4.2Uses 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 modes. • Save Data in CSV files. • Pulse Generation: • Single/Train/Chirp. • Square/Sine waveforms. • Tukey/Hanning Envelopes. • Pulse frequency 20 Hz to 22.05 kHz. • Pulse duration up to 1 s. • MAP – Visualise the echo. Colour or Black and White. Pixel value from RMS or absolute value. New line for each echo trace. Move device whilst pulse-echoing to generate a map. • Fast Fourier Transform (FFT) of 8192 data points to determine frequency content between echo detect lines. • Peak frequency detection • FFT Averaging For Indication Only. Use Ear Protection if required. Due to the limits of the typical microphone dB range on most devices, distant echo signal are likely to be too weak to detect clearly unless extra amplification or a strong echo is present. For fun/educational/research use. This is not ultrasound and NOT suitable for any medical imaging. This app can create annoying loud sounds, so use ear protection if required.
