The relationship between pitch and frequency. The important point is that the same pitch distance/interval (i.e. octave) corresponds to an increasingly larger frequency distancePitch is the perceived fundamental frequency of a sound. While the actual fundamental frequency can be precisely determined through physical measurement, it may differ from the perceived pitch because of overtones, or partials, in the sound. The human auditory perception system may also have trouble distinguishing frequency differences between notes under certain circumstances. According to ANSI acoustical terminology, it is the auditory attribute of sound according to which sounds can be ordered on a scale from low to high.
Pitches may be described in various ways, including high or low, as discrete or indiscrete, pitch that changes with time (chirping) and the manner in which this change with time occurs: gliding; portamento; or vibrato, and as determinate or indeterminate. Musically the frequency of specific pitches is not as important as their relationships to other frequencies — the difference between two pitches can be expressed by a ratio or measured in cents. People with a sense of these relationships are said to have relative pitch while people who have a sense of the actual frequencies independent of other pitches are said to have "absolute pitch", or "perfect pitch".
During historical periods when instrumental music rose in prominence (relative to the voice), there was a continuous tendency for pitch levels to rise. This "pitch inflation" seemed largely due to instrumentalists competing with each other, each attempting to produce a brighter, more "brilliant", sound than that of their rivals. (In string instruments, this is not all acoustic illusion: when tuned up, they actually sound objectively brighter because the higher string tension results in larger amplitudes for the harmonics.) This tendency was also prevalent with wind instrument manufacturers, who crafted their instruments to generally play at a higher pitch than those made by the same craftsmen years earlier.
It should be noted too that pitch inflation is a problem only where musical compositions are fixed by notation. The combination of numerous wind instruments and notated music has therefore restricted pitch inflation almost entirely to the Western tradition.
On at least two occasions, pitch inflation has become so severe that reform became needed. At the beginning of the 17th century, Michael Praetorius reported in his encyclopedic Syntagma musicum that pitch levels had become so high that singers were experiencing severe throat strain and lutenists and viol players were complaining of snapped strings. The standard voice ranges he cites show that the pitch level of his time, at least in the part of Germany where he lived, was at least a minor third higher than today's. Solutions to this problem were sporadic and local, but generally involved the establishment of separate standards for voice and organ ("Chorton") and for chamber ensembles ("Kammerton"). Where the two were combined, as for example in a cantata, the singers and instrumentalists might perform from music written in different keys. This system kept pitch inflation at bay for some two centuries.
In 1939, an international conference recommended that the A above middle C be tuned to 440 Hz, now known as concert pitch. This standard was taken up by the International Organization for Standardization in 1955 (and was reaffirmed by them in 1975) as ISO 16. The difference between this and the diapason normal is due to confusion over which temperature the French standard should be measured at. The initial standard was A = 439 Hz, but this was superseded by A = 440 Hz after complaints that 439 Hz was difficult to reproduce in a laboratory owing to 439 being a prime number.
Despite such confusion, A = 440 Hz is arguably the most common tuning used around the world. Many, though certainly not all, prominent orchestras in the United States and United Kingdom adhere to this standard as concert pitch. In other countries, however, higher pitches have become the norm: A = 442 Hz is common in certain continental European and American orchestras (the Boston symphony being the best-known example), while A = 445 Hz is heard in Germany, Austria, and China.
In practice, as orchestras still tune to a note given out by the oboe, rather than to an electronic tuning device (which would be more reliable), and as the oboist may not have used such a device to tune in the first place, there is still some variance in the exact pitch used. Solo instruments such as the piano (which an orchestra may tune to if they are playing together) are also not universally tuned to A = 440 Hz. Overall, it is thought that the general trend since the middle of the 20th century has been for standard pitch to rise, though it has been rising far more slowly than it has in the past.
