Ledger line
From Free net encyclopedia
A ledger line or leger line is a tool of musical notation to express notes that do not fall on the regular lines or spaces of the musical staff. A short line (slightly longer than the note) is drawn parallel to the lines on the staff (above or below as appropriate), corresponding to where the staff line would be if the note were in range (see Figure 1).
Notes on more than three or four ledger lines off the staff are usually considered too hard to read, and if there are several measures of them, it is usually preferred to switch clef or use 8va notation. Some transposing instruments (such as the piccolo and the double bass) transpose at the octave in order to avoid ledger lines.
However, for some other instruments, the players prefer the use of ledger lines over a clef they're unfamiliar with. For example, on the clarinet the player would rather see ledger lines for the chalumeau register instead of the bass clef, while flautists prefer ledger lines for the higher notes instead of 8va notation.