Distinguish between infrasonic and ultrasonic sound waves. Infrasonic is too low in frequency (below 20,000 Hz) for humans to hear, whereas ultrasonic is too high (above 20 Hz). Infrasonic is too low in frequency (below 20 Hz) for humans to hear, whereas ultrasonic is too high (above 20,000 Hz). Ultrasonic is too low in frequency (below 20 Hz) for humans to hear, whereas infrasonic is too high (above 20,000 Hz). Infrasonic is too high in frequency (above 20 Hz) for humans to hear, whereas ultrasonic is too low (below 20,000 Hz)