Apple Logic Pro 9 - Manual (Page 857)

The global Transpose track transposes Apple Loops used on audio tracks by a maximum
of that great when transposed over a greater range. This is also true for the Transposition
parameter of the Region Parameter box.
Apple Loops Transpose to the Wrong Octave
Transposing an Apple Loops file to a higher pitch may result in the loop being played
back at a lower pitch, and vice versa.
For example, if an Apple Loops file is transposed to sound seven semitones higher, it will
actually play back five semitones lower. This is harmonically correct transposition, but it’s
probably not to the intended octave.
Transposing audio material is a technically complicated process that always implies a
certain loss in quality. The greater the transposition range, the more significant the loss
in quality. This is why Apple Loops are always transposed by the smallest possible value.
You should note that sound quality is dependent on the transposition amount of the
Apple Loops file’s original key—not the project key, which defines the zero line of the
Transposition track. For example, if the project key is already five semitones above the
original key of an Apple Loops file, setting the transposition value to +2 will transpose
the Apple Loops file downwards by ten semitones. This is because the transposition value
is only five semitones below its original key (rather than seven semitones above it).
In the classical European music system, an octave is divided into 12 semitones. As
+7 semitones is harmonically equal to −5 semitones, a value of −5 is used as the
transposition amount. The same happens with other settings: A transposition value of
−9 will result in +3, and +12 will result in ± 0. The use of the nearest harmonically equal
transposition option is based on delivering the best sonic results, with smaller
transpositions being desirable.
Converting Apple Loops to Audio Files
When you convert an Apple Loops file into an audio file, the resulting file may not play
at the project’s current tempo and key settings. Rather, the new audio file will play at the
original tempo and key of the Apple Loops file.
This happens when you select an Apple Loops file and choose Audio > Convert Regions
to New Audio Files from the local Arrange menu, and change the File Format parameter
in the ensuing window to AIFF. This creates a copy of the original Apple Loops file, but
without the transient and category tags. The lack of these tags restricts file playback to
the originally recorded tempo and key of the Apple Loops file—not the tempo and key
of the project.
857 Chapter 30 Creating Apple Loops