Foot pitch

What it means

The foot pitch (German Fußtonzahl) indicates in which octave register an organ stop sounds. It refers to the length of the longest open pipe of the stop, measured in feet. An eight-foot stop sounds as the key is notated; four-foot sounds an octave higher, two-foot two octaves higher, sixteen-foot an octave lower, thirty-two-foot two octaves lower. Intermediate values also occur: stops with fractional numbers such as two and two-thirds or one and three-fifths feet sound not in octaves but in fifths and thirds above the fundamental and are called mutations.

Musical use

The foot pitch is the ordering principle of every registration. From it follows how high or low a sound lies and how it is built up: a foundation stop of eight feet forms the basis, supplementary stops in four and two feet give brilliance, mutations colour the sound by reinforcing individual overtones. In this way the organist builds up tone colours, similar to the way a note is composed of partials. In the pedal, sixteen feet is the usual basis. The indications stand on every stop knob and are comparable from organ to organ, even when the stop names change.

Performance practice

When registering, begin with the question of the desired register and choose the foundation stop before you add colour. Check whether a combination of mutations suits the piece — they are effective but can blur the polyphony. High stops quickly become shrill in dense chords; keep the spacing open then. In the pedal, the balance between sixteen and eight feet is decisive for clarity. Note your registrations with foot pitches instead of only with names, because the designations differ on other instruments but the numbers remain transferable.

Remember that stopped stops produce the same pitch at half the length as open ones: a stopped eight-foot stop is only about four feet long but sounds at the notated pitch. The foot pitch therefore always designates the sounding register and not the measured pipe length. On an unfamiliar instrument, check the stop labels and assign them to the families before you register. With mutations, careful trying out is worthwhile, because their effect depends on the foundation stop with which they are combined.