Microtones are those intervals that are smaller than a semitone; human voices and unfretted strings can easily produce them by going in between the " normal " notes, but other instruments will have more difficulty the piano and organ have no way of producing them at all, aside from retuning and / or major reconstruction.
32.
"' Lute "'( ) can refer generally to any string instrument having the strings running in a plane parallel to the sound table ( in the Hornbostel Sachs system ), more specifically to any plucked string instrument with a neck ( either fretted or unfretted ) and a deep round back, or more specifically to an instrument from the family of European lutes.
33.
Under the strings of tanpuras, which are unfretted ( unstopped ), and occasionally under those bass drone strings of sitars and surbahars which are seldom fretted, cotton threads are placed on the " javari " bridge to control the exact position of the node and its height above the curved surface, in order to more precisely refine the sound of " javari ".
34.
In his " Kitab al-Shifa " ( Book of Soul Healing ), he proposed another taxonomy, of five classes : fretted instruments, unfretted ( open ) stringed, lyres and harps, bowed stringed, wind ( reeds and some other woodwinds, such as the flute and bagpipe ), other wind instruments such as the organ, and the stick-struck santur ( a board zither ).
35.
From the standpoint of musical acoustics and scientific terminology, some instruments, such as slide trombones, unfretted bowed-string instruments, guitars played with slides and, of course, slide whistles, can change the frequency of their notes continuously, while others, notably acoustic keyboard instruments, are restricted to quantized ( stepped ) changes in pitch . ( The clavichord's " Bebung " is the one exception, but that is essentially ornamentation of a single pitch, not a glide . ) Some instruments, such as the clarinet and saxophone, can produce a continuous pitch ( frequency ) change, although their characteristic design is to provide distinct pitches.
