VADD — Volcano Auditory Display Device

Ted Apel and Jeffrey Johnson

A portable real-time infrasound sonification device built on the Teensy 3.6 microcontroller. VADD transposes sub-audible infrasonic signals (below 20 Hz) into the audible range using frequency modulation, allowing researchers to listen to volcanic activity in the field.

The sonification algorithm is written in Faust and compiled to C++ for the Teensy Audio Library. An infrasonic microphone captures low-frequency pressure waves, which are low-pass filtered, scaled, and used to frequency-modulate a carrier oscillator. Bandstop filters remove the unmodulated carrier frequency, leaving only the sonified infrasonic content.

Hardware

• Teensy 3.6 with Audio Shield
• Infrasonic microphone (electret with sub-20 Hz response)
• Two potentiometers: carrier frequency and modulation depth
• Volume knob (added in v3)
• PAM8302A amplifier module

The circuit design is in circuit/VADD_v2.0.fzz (Fritzing format).

Software

• sonify.dsp — Faust source code for the sonification algorithm
• sonify.cpp — Generated C++ (compiled with faust2teensy sonify.dsp)
• sonify.h — Generated header
• infrasonic_03.ino — Arduino/Teensy sketch (v3, with volume control)

Version History

1. v1 — Sonification implemented directly in Teensy Audio Library
2. v2 — Algorithm rewritten in Faust, compiled to Teensy Audio object
3. v3 (2025) — Added volume knob

Publications

Apel, T. & Johnson, J. (2021). Portable Realtime Volcano Infrasound Auditory Display Devices. Proceedings of the 26th International Conference on Auditory Display (ICAD 2021). PDF | Video