The phrase "too high for human ears or hearing" refers to sounds that are outside the range that humans can hear. There are several synonyms that can be used to describe these types of sounds, including ultrasonic, inaudible, beyond the range of human hearing, and supersonic. Ultrasonic refers to sounds that have a frequency greater than the upper limit of human hearing, which is typically around 20kHz. Inaudible refers to sounds that are unable to be heard by the human ear. Beyond the range of human hearing and supersonic both indicate that the sounds are above the limits of human auditory perception.