Audio frequency

An audio frequency or audible frequency is a periodic vibration whose frequency is audible to the average human. The SI unit of frequency is the hertz. It is the property of sound that most determines pitch.
The generally accepted standard hearing range for humans is 20 to 20,000 Hz. In air at atmospheric pressure, these represent sound waves with wavelengths of to. Frequencies below 20 Hz are generally felt rather than heard, assuming the amplitude of the vibration is great enough. Sound waves that have frequencies below 20 Hz are called infrasonic and those above 20 kHz are called ultrasonic.
Sound propagates as mechanical vibration waves of pressure and displacement, in air or other substances. In general, frequency components of a sound determine its "color", its timbre. When speaking about the frequency of a sound, it means the property that most determines its pitch. Higher pitches have higher frequency, and lower pitches have lower frequency.
The frequencies an ear can hear are limited to a specific range of frequencies. The audible frequency range for humans is typically given as being between about 20 Hz and 20,000 Hz, though the high frequency limit usually reduces with age. Other species have different hearing ranges. For example, some dog breeds can perceive vibrations up to 60,000 Hz.
In many media, such as air, the speed of sound is approximately independent of frequency, so the wavelength of the sound waves is approximately inversely proportional to frequency.

Frequencies and descriptions

MIDI note	Frequency	Description	Sound file
0	8.17578125	Lowest organ note	n/a
12	16.3515625	Lowest note for tuba, large pipe organs, Bösendorfer Imperial grand piano	n/a
24	32.703125	Lowest C on a standard 88-key piano
36	65.40625	Lowest note for cello
48	130.8125	Lowest note for viola, mandola
60	261.625	Middle C
72	523.25	C in middle of treble clef
84	1,046.5	Approximately the highest note reproducible by the average female human voice
96	2,093	Highest note for a flute
108	4,186	Highest note on a standard 88-key piano
120	8,372
132	16,744	Approximately the tone that a typical CRT television emits while running.