| Dbl Contra | style="text-align: center" | Sub Contra | style="text-align: center" | Contra | style="text-align: center" | Great | style="text-align: center" | Small | style="text-align: center" | 1 Line | style="text-align: center" | 2 Line | style="text-align: center" | 3 Line | style="text-align: center" | 4 Line | style="text-align: center" | 5 Line | style="text-align: center" | 6 Line | |- ! style="text-align: right" | MIDI Note | style="text-align: center" | 0 | style="text-align: center" | 12 | style="text-align: center" | 24 | style="text-align: center" | 36 | style="text-align: center" | 48 | style="text-align: center" | 60 | style="text-align: center" | 72 | style="text-align: center" | 84 | style="text-align: center" | 96 | style="text-align: center" | 108 | style="text-align: center" | 120 | |} Ottava alta and bassa The notation 8a or 8va is sometimes seen in sheet music, meaning "play this an octave higher than written" (all' ottava: "at the octave" or all' 8va). 8a or 8va stands for ottava, the Italian word for octave (or "eighth"); the octave above may be specified as ottava alta or ottava sopra). Sometimes 8va is used to tell the musician to play a passage an octave lower (when placed under rather than over the staff), though the similar notation 8vb (ottava bassa or ottava sotto) is also used. Similarly, 15ma (quindicesima) means "play two octaves higher than written" and 15mb (quindicesima bassa) means "play two octaves lower than written." The abbreviations col 8, coll' 8, and c. 8va stand for coll'ottava, meaning "with the octave", i.e. to play the notes in the passage together with the notes in the notated octaves. Any of these directions can be cancelled with the word loco, but often a dashed line or bracket indicates the extent of the music affected. Equivalence After the unison, the octave is the simplest interval in music. The human ear tends to hear both notes as being essentially "the same", due to closely related harmonics. Notes separated by an octave "ring" together, adding a pleasing sound to music. The interval is so natural to humans that when men and women are asked to sing in unison, they typically sing in octave. For this reason, notes an octave apart are given the same note name in the Western system of music notation—the name of a note an octave above A is also A. This is called octave equivalence, the assumption that