Instruments which are not notated at their true pitch but (mechanically and without any effort on the player's part) produce the effect of that pitch. For example, the cl. is made in several sizes, the B♭ and A being the most often used because these keys reduce the difficulty of playing in the flat and sharp keys, respectively, by reducing the number of flats or sharps with which the player has to cope. In the B♭ instr., that key is to its player the ‘natural key’ (as C is to the pianist): the player faced with music in (say) the key of E♭ finds the music written in the key of F, i.e. there are 2 flats fewer to consider. Similarly with the A instrument a piece written in the key of B is notated in the key of D, i.e. there are 3 sharps fewer to consider. Thus music for the B♭ cl. is notated a tone higher than it is to sound and music for the A cl. a minor 3rd higher. Many players, with improved mechanism and developed technique, use the B♭ instrument for all keys, making the transposition mentally. On the rare C cl. the note sounded is the note written; the E♭ cl. transposes 1½ tones higher than written note; the bass clarinet in B♭ an octave and a tone lower.
The transposing instruments are as follows: