Apple Logic Pro 9 - Manual (Page 976)

2 Draw a line (between notes) where you want to separate the voices.
Notes below the line are moved to the MIDI channel below their current assignment.
3 If you make a mistake, move the mouse back slightly to the left.
The separation line is erased to the right of the tool, allowing you to try again.
Staff Style Examples
The following sections illustrate how you can use the staff style features to meet specific
notation needs.
Creating a Staff Style for Two Independent Voices
If there are two independent voices throughout the piece, the parameters might be set
as follows: stem, tie, and N-tuplet direction are set to Up for the top voice and Down for
the bottom voice. Note that even with these general parameters, note attributes can be
changed for each note. (See
Using Note Attributes to Change Individual Notes .) Both
voices are displayed with automatically displayed rests (Rest parameter: Show).
Creating a Single Staff Style with Optional Polyphony
Sometimes you need to add a second voice to a staff that usually only requires one voice,
in order to properly notate a short, rhythmically independent passage. This is not
uncommon with orchestral scores, in which the unison part for a group of instruments
is temporarily separated from the other parts.
976 Chapter 31 Working with Notation