audio frequency (AF)
Audio Frequencies(AF) are sinusoidal sound waves in the audible frequency range between 20 Hz, corresponding to a very low tone, and 20 kHz, for extremely high tones. One of the reference tones is the concert pitch a' at 440 Hz.
Tones are pressure waves that are transmitted in the air at a speed of 331 m/s. The resulting wavelengths range from a low frequency to a high frequency. The resulting wavelengths are between 16 m for low tones and 16 cm for high tones. Frequencies above 20 kHz are called ultrasound; frequencies below 20 Hz are called infrasound.