Eight foot pitch
An organ pipe, or a harpsichord string, designated as eight-foot pitch is sounded at standard, ordinary pitch. For example, the A above middle C in eight-foot pitch would be sounded at 440 Hz (or at some similar value, depending on how concert pitch was set at the time and place the organ or harpsichord was made).
Similar terms
Eight-foot pitch may be contrasted with four-foot pitch (one octave above the standard), two-foot pitch (two octaves above the standard), and sixteen-foot pitch (one octave below the standard). The latter three pitches were often sounded (by extra pipes or strings) along with an eight-foot pitch pipe or string, as a way of enriching the tonal quality. The numbers just mentioned largely exhaust the possibilities for harpsichords; in organs a far greater variety is possible; see Organ stop.
The reason these lengths can all be obtained by successive doubling is that, all else being equal, a pipe or string that is double the length of another will vibrate at a pitch one octave lower.
