Infrasound is sound below the audible range of human hearing. Sound at these low frequencies can excite structures and these structures in movement may radiate some sounds in the audible range. CSTi acoustics can measure sound levels at frequencies as low as 1 Hz.

Examples of such sounds are combustion turbine exhausts, HRSG structures and exhausts, jet engine test cells, and wind turbines.

Ultrasound is sound above 20 kHz, the upper human range of human hearing. CSTI acoustics can measure sound levels at frequencies as high as 90 kHz.

CSTI acoustics measured the noise, vibration, and ultrasound exposure of mice and rats in specialized housing facilities for M.D. Anderson.