### A3/A4 = The Prime Octave.

When talking or writing a lot about tuning, descriptive shortcuts are inevitable.  Referring to the A3/A4 octave as the “Prime” octave came about as one of those shortcuts.  Soon after that, the term ‘Sub-Prime’ was used to describe or identify the octave below the prime octave.  The A2-A3 octave.

Those terms are not only used for the A3/A4 and the A2/A3 octaves but are also used for the intervals within those ranges.  The ‘prime’ octave is referred to as both an interval and as a ‘range’ of notes (A3-A4) between and including A3 & A4.  The ‘subprime’ refers to the interval A2/A3, and the range of notes (A2-A3) between and including A2 & A3.

It just makes it easier to talk about the prime 5ths which, for our purposes, are the lower prime 5th (A3/E4) and the upper prime 5th (D4/A4).  The sub-prime 5ths being the A2/E3 (lower) and D3/A3 (upper).

When written, I try to use a distinction between the interval and the range of notes:
When a ” / “ is used between two notes, it is an interval.   A3/A4 is the interval of an octave.   The prime octave A3/A4.
When a ” – “ is used between two notes it is a range of notes.   A3-A4 is the range of notes between and including A3 and A4.