The middle register is the eleven consecutive semitones from low A ( 0 123 45 ) to A flat or G sharp ( 123 456 or alternatively 23 456 ). All these notes have the thumbhole closed or open and all speak easily if not tongued too hard.
Play the series of notes slowly, evenly and in a detached manner (i.e. with a small silence between each note), taking care to tongue each note clearly (we recommend a soft 'tu' sound as in 'tup' which should rhyme with 'cup'). Each note should have a sweet warm tone.
This exercise is not about speed, but about tone quality. Concentrate on trying to 'hear' each note before you play it.
You can make the exercise more difficult, by playing in a more legato manner (i.e. where there is no gap between each note) and by playing the note sequence more quickly.
You should try a variety of tonguing sounds - 'ti' or 'ta' instead of 'tu'. A good player will be able to vary his or her tonguing sound as a means of varying the strength and quality of particular notes.