Humans can hear sounds with frequencies between 20Hz and 20kHz, but in practice most of us hear only up to 16khz. Bats commonly emit echolocation ultrasounds at frequencies between 12kHz and 100kHz. Some bat species can hear up to 160 kHz. Other animal species can hear a full octave above humans, for example cats and dogs can hear up to 40kHz. Some animal species can hear several octaves below humans. Moles, for example, can hear frequencies of a only a few hertz.

"070703" was recorded by Joe Gilmore on 07.07.03 with a Tuneable Heterodyne Ultrasonic Microphone [20 - 120kHz] in Wakefield, England. I recorded the sounds of 10 objects which i have laying around my house: some rocks, a bed spring, a small loudspeaker, a singing bowl, a bell, some nails, glass.

The final piece was realised using Max/msp.

I am grateful to Liz Higgs from the North Yorkshire Bat Group for the loan of her ultrasound microphone and John Kannenberg for his patience.