TC-Helicon VoicePro - Manual (Page 65)

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Section 7: Optimizing Hybrid TM Pitch Shifting
Introduction
Whenever you enable the Pitch Block or load a preset with
it enabled, you are using VoicePro's Hybrid Shifting
TM
algorithm. The Hybrid Shifting TM algorithm is a proprietary
TC-Helicon technique that provides four main benefits:
• It is more natural and transparent than other pitch shifting
techniques for voice
• It has a wider usable shift range
• It has the ability to emulate the sound of other pitch
shifting techniques
• It is integrated with VoiceModeling TM for manipulating
voice character
This section discusses ways to get the best from our pitch
shifting algorithm
In this section we cover:
• Background on non-Hybrid Pitch TM Shifting Techniques
• Understanding the Hybrid Shifting TM parameters
• Working with small shift intervals
• Raising the pitch most effectively
• Lowering the pitch most effectively
• Emulating the sound of other shifting algorithms
Background on non-Hybrid TM Pitch
Shifting Techniques
If you're interested in understanding why the Hybrid
Shifting
TM algorithm offers its four main benefits, it's helpful
to get an understanding by comparing it to other pitch
shifting techniques. If you want to get the benefits right
away, skip to "Understanding the Hybrid Shifting
TM
parameters".
There are two pitch shifting algorithms most prevalent in
audio production; the technique we refer to as Instrumental
(non formant-corrected) Pitch Shifting and PSOLA (or
formant-corrected) Pitch Shifting.
“Instrument” Pitch Shifting
Instrument Pitch Shifting resamples the frequency scale of
an audio signal. Reading and writing samples at different
rates can alter the pitch of the audio signal. Instrumental
Pitch Shifting is not suited to processing the human voice
when shifting by more than a few semitones. The human
voice contains resonant frequencies called formants which
are responsible for the perception of different vowels and
the overall character of the voice. The formant structure of
the human voice is due to the shape of the vocal tract and
is not affected by fluctuations in pitch. Instrumental Pitch
Shifting shifts the entire vocal signal including formants,
which causes the naturalness of a pitch-shifted voice to
decrease as the shift amount increases.
Due to the limitations of the Instrument Pitch Shifting
technique, the number of music and dialog production
applications is limited. In music production, the technique is
used for correcting mild intonation errors (pitch correction)
or for detune effects where the overall shift is less than 100
cents (100 cents = 1 semitone). In this instance, the
degradation of natural formant quality is less apparent. In
dialog production, the instrumental technique is employed
when natural formant quality is not important. This is
popular for animated character effects that do not need to
conform to the formant structure of the human voice.
“PSOLA” Pitch Shifting
PSOLA Pitch Shifting is a formant-corrected vocal pitch
shifting method that works by changing the pitch of the
human voice without altering the formant frequencies. By
detecting the pitch of a voice, it can be windowed and cut
out at a pitch synchronous rate and then pasted back in at
a different rate. This process causes the pitch of the signal
to be altered while maintaining the original formant
structure. The primary drawbacks of PSOLA Pitch Shifting
are the audible artifacts created by incorrect detection of
input pitch as well as buzziness when the pitch is shifted
down by an octave or more.
PSOLA shifting is mainly used in music production on non-
lead vocal effects. Non-lead vocal parts include harmony
parts and octave doubling. These pitch-shifted voices can
be mixed at a level sufficiently low relative to the lead vocal
that the artifacts are not exposed. For dialog production,