User`s manual

9
As you can see, the intervals in the Equal Tempered Scale are NOT equal to
the harmonious integer ratios. Rather, the Equal Tempered Scale is a
compromise. It became widely used because once a harpsichord or piano is
tuned to that scale, any composition in any key could be played and no
one chord would sound better or worse than that same chord in another
key.
How Auto-Tune 3 detects pitch
In order for Auto-Tune 3 to automatically correct pitch, it must first detect
the pitch of the input sound. Calculating the pitch of a periodic waveform
is a straighforward process. Simply measure the time between repetitions
of the waveform. Divide this time into one, and you have the frequency in
Hertz. Auto-Tune 3 does exactly this: It looks for a periodically repeating
waveform and calculates the time interval between repetitions.
The pitch detection algorithm in Auto-Tune 3 is virtually instantaneous. It
can recognize the repetition in a periodic sound within a few cycles. This
usually occurs before the sound has sufficient amplitude to be heard. Used
in combination with a slight processing delay (typically about 1 to 10
milliseconds), the output pitch can be detected and corrected without
artifacts in a seamless and continuous fashion. (Although it must be kept
in mind that some plug-in protocols introduce a certain amount of inher-
ent and unpredictable delay that depends largely on what else your CPU is
doing at the time.)
Auto-Tune 3 was designed to detect and correct pitches up to the pitch C6.
(If the input pitch is higher than C6, Auto-Tune 3 will occasionally inter-
pret the pitch an octave lower. This is because it interprets a two cycle
repetition as a one cycle repetition.) On the low end, Auto-Tune 3 will
detect pitches as low as 25Hz (when the Bass Instrument Input Type is
selected). This range of pitches allows intonation correction to be per-
formed on virtually all vocals and instruments.
Of course, Auto-Tune 3 will not detect pitch when the input waveform is
not periodic. As demonstrated above, Auto-Tune 3 will fail to tune up
even a unison violin section. But this can also occasionally be a problem
with solo voice and solo instruments as well. Consider, for example, an
exceptionally breathy voice, or a voice recorded in an unavoidably noisy
environment. The added signal is non-periodic, and Auto-Tune 3 will have
difficulty determining the pitch of the composite (voice + noise) sound.
Luckily, there is a control (the Tracking control, discussed in Chapter 3)
that will let Auto-Tune 3 be a bit more casual about what it considers
“periodic.” Experimenting with this setting will often allow Auto-Tune 3
to track even noisy signals.
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