Apple Logic Express 8 - Manual (Page 538)

538 Chapter 21 Editing Audio in the Sample Editor
This means that the original timbre (or the physical size of the resonance body) is
maintained, resulting in a more natural sounding transposition. The only trade-off is
that calculation takes more time.
Note: The quality of Harmonic Correction is heavily dependent on the source material,
because the algorithm has to make intelligent decisions between tonal and atonal
components of the recording, and handle them separately. This is not an exact science,
and is more accurate on monophonic material than complex stereo material, but you
can certainly use it on a complete mix. The phase correlation of stereo recordings is
maintained.
Harmonic
If Harmonic Correction is turned on, you can also use the Harmonic (Shift) parameter to
independently alter timbre. The units are shown in cents—100 cents per semitone.
 If you select the same value in both the Harmonic and Transposition fields, no
correction occurs, and the result is as if Harmonic Correction is switched Off.
 If you set Harmonic to zero, the formants don’t change. This avoids the unwanted
side effects of traditional pitch shift algorithms.
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Tip: If you need to find the exact transpose value by trial and error, switch off Harmonic
Correction. As soon as you’ve found the right transposition value, do an independent
Harmonic Correction, with the same value, in a second step.
Shifting Formants Without Transposition
You can also use Harmonic Correction to shift the formants without transposition. This
means you can alter the physical size of the sound source’s resonance body—to give
female voices a male character and vice versa, for example—while keeping the pitch in
tune.
This remarkable effect (sometimes known as gender-bending) allows you to change
sounds so that they appear to have been made by unusually small or large instruments.
It is useful for beefing-up thin or brittle sounding parts, such as guitars, or instruments
and vocals that were recorded through a microphone with a limited frequency
response.
As a usage example on a vocal part: If you set Harmonic Shift to –300, and the
Transposition value to zero, the sonic character of the singer will be changed as though
transposed three semitones down—but without an actual transposition in pitch. This
means that a musical C remains a C, but the timbre of the vocal becomes darker.