register

A register is a segment of an instrument's or voice's total range that has a characteristic quality or timbre. The clarinet, for example, has three distinct registers: the warm, dark chalumeau register (low), the bright clarion register (middle), and the shrill altissimo register (high). Each sounds almost like a different instrument. In vocal music, registers describe the different mechanisms used to produce sound. The chest voice (lower register), head voice (upper register), and falsetto each have distinct tonal qualities. The passaggio — the transition zone between registers — is where the voice must smoothly shift from one production mechanism to another, and navigating this transition is one of the central challenges of vocal training.