Their days are spent in the studio, on tour, in rehearsals, or practicing their vocal (or in some cases), instrumental, or dance skills. The Singer must first and foremost learn the vocal parts to the music and be able to perform them at a high level. They must master many techniques beyond just singing the parts, for example proper microphone techniques, movement, and how to follow a Conductor. They also need to take good care of their voice, since their instrument is uniquely a part of their body.
