Each place in the world has a unique and diverse infrasonic ambience. Although many places share common sources, such as volcanoes, meteors, and storms, the local conditions can lend a listening station a distinctive character. In early infrasound literature, the rich ambient sound field was referred to as the infrasonic zoo, alluding to the variety of exotic beasts captured by our listening systems. The specialist spends hours, sometimes days, examining a particular sound specimen in hopes of inferring where it came from and how it was made. Our ears are remarkable signal processing tools that allow us to recognize very small changes in amplitude and frequency, but only within our hearing range (20Hz-20kHz). One of the techniques we use to grasp these inaudible sounds is to make them audible through time compression (speeding up), pitch shifting (frequency transposition), or other methods.
This page presents examples of sounds recorded by a variety of infrasound recording systems. Signal processing algorithms were used to make them audible and occasionally pleasant. Many of the sound files are complex, and superpose breaking waves, distant storms, aircraft, and volcanoes.
Since most of the ISLA stations are in island environments, I suggest you explore the Ocean gallery first and get acquainted with the infrasound from breaking surf. Atmosphere and Earth provide sounds from aircraft, spacecraft, meteors, earthquakes, and volcanoes. On this intro page, we have placed the sound signature of the Sumatra earthquake and tsunami. The first signal is the earthquake (Earth), the second is the sound of the earthquake traveling through the ocean (t-wave), and the third and last is the infrasound propagating through the atmosphere and produced by the earthquake and tsunami (Atmosphere and Ocean).
To best enjoy your visit to the infrasound zoo, turn up your bass to the max.
Sumatra Earthquake Wavefield: Seismic, Hydroacoustic, and Infrasonic (in that order).