Logic Pro 9 User Manual - Help Library - Apple

Using the Sample Editor’s “Time and Pitch Machine”
You can use the “Time and Pitch Machine” to radically alter the time structure of audio
files, including time compression or expansion, and pitch transposition. When changing
the pitch, you can also correct any alteration of the formants—the vocal characteristics
of the pitch-shifted audio. Pitch shifting without formant correction causes a phenomenon
commonly known as the Mickey Mouse effect.
In the “Time and Pitch Machine,” time and pitch functions can be carried out together,
or can be performed independently of one another.
The Technology of the “Time and Pitch Machine”
The “Time and Pitch Machine” analyzes the spectral components and dynamics of the
digital audio material and processes the result. The algorithm endeavors to retain as
much spectral and dynamic information as possible, and minimizes phase variations.
In stereo files, the phase relationship between the left and right channels is fixed, and
not altered. Doubled sound events are kept to a minimum.
You should bear in mind, however, that apart from resampling (transposition), the “Time
and Pitch Machine” has to achieve the “physically impossible”: When a sample is
lengthened, information needs to be invented. Equally, when a sample is shortened,
information has to be cut out. The process of lengthening is more difficult than
shortening, and if you have a choice, it’s better to speed up a drum loop than to slow
it down.
There’s always a small deviation between the set stretch factor and the actual result.
However, this deviation is only a few milliseconds or fractions of a bpm. Also, because
the absolute deviation is independent of the length of the processed section, it is no
greater in longer files.
Opening the Sample Editor’s “Time and Pitch Machine”
You need to select an area within an audio file before you can open the “Time and Pitch
Machine.”
To open the “Time and Pitch Machine”
1 Select the area of the audio region in the Sample Editor that you want to process through
the “Time and Pitch Machine.”
2 Choose Factory > “Time and Pitch Machine” (or use the corresponding key command,
default assignment: Control-P).
576 Chapter 17 Editing Audio in the Sample Editor