Under the Helmholtz Octave Designation System, a name applied to the octave which extends from C

This octave can also be designated with two hash marks (i.e. C'') or in the fifth octave under Acoustical Society of America system (i.e. C_{5}). The MIDI Octave Designation System has two versions, one where note 1 (8.176 Hz) is octave "0" making the **Two-line** octave the sixth octave (i.e. C6), and the other with note 1 (8.176 Hz) at octave "-2" making the **Two-line** octave the fourth octave (i.e. C4).

The indication 8va (shown below) can be used to represent the same pitches.

## Play Two-line Octave Example (MIDI file format) |

More about octave designations - More about pitch