Fundamentals of music(pitch)

Pitch

Pitch is a subjective sensation, reflecting generally the lowness (slower wave frequency) or highness (faster wave frequency) of a sound. Most people appear to possess relative pitch, which means they perceive each note relative to some reference pitch, or as some interval from the previous pitch. Significantly fewer people demonstrate absolute pitch (or perfect pitch), the ability to identify certain pitches without comparison to another pitch. Human perception of pitch can be comprehensively fooled to create auditory illusions. Despite these perceptual oddities, perceived pitch is nearly always closely connected with the fundamental frequency of a note, with a lesser connection to sound pressure level, harmonic content (complexity) of the sound, and to the immediately preceding history of notes heard. In general, the higher the frequency of vibration, the higher the perceived pitch is, and lower the frequency, the lower the pitch. However, even for tones of equal intensity, perceived pitch and measured frequency do not stand in a simple linear relationship.
Below about 1,000 Hz, the perceived loudness of a tone gets lower as sound frequency decreases. Also above approximately 2,000 Hz, the perceived loudness increases as the sound's frequency increases. This is due to the ear's natural sensitivity to higher pitched sound, as well as the ear's particular sensitivity to sound around the 200–400 Hz area, the frequency range most of the human voice occupies.
In Western music, there have long been several competing pitch standards defining tuning systems. Most made a particular key sonorous, with increasingly remote ones more and more problematic; the underlying problem is related to the physics of vibrations.
In addition, fixing notes to standard frequencies (required for instrument makers) has varied as well. Concert A was set at 435 Hz by France in 1859 while in England, concert A varied between 439 and 452 Hz. A frequency of 440 Hz was recommended as the standard in 1939, and in 1955 the International Organization for Standardization affirmed the choice. A440 is now widely, though not exclusively, used as the A above middle C.
The difference in frequency between two pitches is called an interval. The most basic interval is the unison, which is simply two of the same pitch, followed by the slightly more complex octave, which indicates either a doubling or halving of the fundamental frequency.