What is an Octavia on alto sax?

The term "octavia" is not commonly used in the context of the alto saxophone. The alto saxophone has a standard range of approximately two and a half octaves, from low A♭ to high F#. Each octave is divided into twelve semitones, or half steps. The notes within each octave are typically referred to by their letter names (A, B, C, etc.) and their octave numbers (1, 2, 3, etc.).

For instance, the lowest note on the alto saxophone is A♭1, while the highest note is F#3. The octave between these two notes is known as the "first octave" or the "chalumeau register." The second octave, which starts from B♭1, is called the "clarion register," and the third octave, which begins from C#2, is known as the "altissimo register."

The term "octavia" may occasionally be used to refer to the highest note on a saxophone, which would be F#3 on the alto saxophone. However, this usage is not widespread, and the more common term for the highest note on a saxophone is simply "altissimo F#."

In summary, "octavia" is not a commonly used term in the context of the alto saxophone, and the instrument has a standard range of approximately two and a half octaves, typically referred to by their letter names and octave numbers.