Been doing some research on the different frequencies of sound and how to capture them. My thoughts are that there may be sounds frequencies that we are missing that might contain information.
There are some areas that I would like to look into. Infrasonic sounds and Ultrasonic sounds. Infrasonic sounds are anything under 20 Hz and Ultrasonic sounds are anything over 20,000 Hz.
Infrasonic recorders:
Hardware-
Software-
I have found an iPhone app called infrasound recorder. I'll have to do some tests to see if this works at all.
Ultrasonic recorders:
Hardware-
Software-
From the wildlife sound recording site.