Like the flute, the clarinet is an extremely nimble instrument, featuring the same Boehm system of keys levers and springs used on the flute. However, there is an anomaly in the clarinet sound as it comes out considerably deeper than one would expect for an instrument of this size. This is because it acts as a stopped pipe, the vibrating column of air being a U-shaped one, twice the length of the instrument. This gives a pleasant woody, hollow sound in the bottom register which is easy to learn and admits of fast progress.
However, on the left thumb is a special key, known on the other instruments as an “octave key”. Press this and tighten the embouchure, and suddenly, you're singing soprano. Try this on clarinet and you are in for a shock-the note jumps not eight notes, but twelve. In the upper register one has to re-learn the clarinet. The home sequence of notes in the bottom register is F Major, like a treble recorder, but in the upper register it is C major, like a descant recorder.
Since the clarinet is an instrument of the mid-eighteenth century, it has little baroque or early music, but much has been adapted, with varying degrees of success. It was a highly popular instrument in the 30s and 40s in the hands of the swing masters, but has largely been overshadowed in jazz by its glamorous cousin, the saxophone.