Scientific pitch notation creates a linear pitch space in which an octave spans 12 semitones, where each semitone is the distance between adjacent keys of the piano keyboard. Distance in this space corresponds to musical pitch distance in an equal-tempered scale; 2 semitones being a whole step, 1 semitone being a half step. An equal-tempered semitone can also be subdivided further into 100 cents. Each cent is semitone or octave. This measure of pitch allows the expression of "microtones" not found on standard piano keyboards. The notation is sometimes used in the context of meantone temperament, and does not always assume equal temperament
Uilleann pipes soft D and is accomplished by applying slightly more pressure to the bag and flicking a higher note finger as it is sounded. Pipemakers tune the chanter so the hard D is the in-tune note, the soft D usually being slightly flat. Many chanters are fitted with keys to allow accurate playing of all the semitones of the scale. Four keys will give all the semitones: F, G, B, C. Older chanters usually had another key for producing D (D in the third octave), and often another small key for E, and another for D (as opposed to the E