>The signal peak at 1:55.5 shows the 1/2 second echo very nicely, occurring at 1:56. This is a 4km echo. [... ] I believe this echo originates from this island. Also, This would suggest the Island is quite dense. [...] I believe this hum is seismic. It behaves as if it is traveling through rock and water, and has no origin in air or other medium.<
Quelle: google-Group, hum-sufferers, Audio Analysis of Hum Recordings