The rate of repetition of the CYCLEs of a PERIODIC quantity, such as a SOUND WAVE. Thus, frequency is the inverse of the PERIOD. More generally, frequency can be thought of as the rate of change of PHASE.
Sound at frequencies above the audible range, namely above 20 kHz, audible only to various non-human species. Because of its very short WAVELENGTH in the megahertz range, ultrasound is used as a safe alternative to X-ray photography in medical diagnosis. Ultrasound scanning is sometimes called sonography.
When sounds are conducted separately and independently to each ear via tubes or headphones, the sounds are said to be heard dichotically. In various psychoacoustic experiments, isolation of the function of each ear is desirable, such as in the testing or simulation of BINAURAL HEARING with the PRECEDENCE EFFECT, or in testing preferences for different sounds presented simultaneously to separate ears.
For any PERIODIC wave the wavelength is the distance from a given point in the wave to the corresponding point in the next cycle of the wave, frequently represented by the Greek letter lambda. It may also be thought of as the distance the sound travels in one CYCLE or PERIOD.