The alto saxophone is a transposing instrument in the key of E♭ . This means that when the alto sax plays a C on the staff, we hear the E♭ below this, or a major 6th below. To play in the same key as other instruments, the alto saxophonist must transpose the music up a major 6th. For example, if a piece of music is written for the C flute, an alto saxophonist must transpose it up a major 6th to make it sound at the same pitch level.