11.3

NEPTUNE PITCH ADJUSTER AND VOICE SYNTH612
Using Formant control
What are formants?
Formants can be described as a sonic “footprint” of an acoustic space. The practical effect of formants could be com-
pared to a multi-peak filter acting on the frequencies in a sound. An acoustic guitar, for example, has a body shape
which makes is sound the way it does. The same goes for a human vocal tract (throat and mouth cavity); every human
vocal tract has a unique “shape” which gives the voice its character. It is these shapes that produce formants. A big
difference between a vocal tract and a guitar body, though, is that the vocal tract changes shape as you sing different
vowels. This also means that the formants will change.
When you pitch shift a signal up or down, the formant “multi-peak filter” will move up or down with the signal fre-
quency (just like a traditional synthesizer filter would with full keyboard tracking activated). The result will be a signal
that not only is pitched but also changes character. In some situations this might be what you want, but when it
comes to pitch shifting vocals you will probably often want the pitch-shifted signal to sound like it’s sung by the same
person. Therefore, Neptune features a formant control function.
The Formant section in Neptune lets you control the formants so they don’t move along with the pitched signals.
Neptune continuously samples and analyses the input audio and determines both the pitch and the current formants
of the signal in real-time. The formants are then automatically applied to the pitch-adjusted output signal in real-time.
The picture below shows schematic examples of a 500 Hz signal, pitch-shifted down and up one octave respectively,
without and with formant correction. The formants are the peaks of the gray dotted lines in the graphs:
Pitch-shifting without and with formant correction applied. The left column shows -1 octave pitch-shifting and the right column +1
octave.
0 1000 2000 3000 4000 f (Hz)
dB
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dB
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0 1000 2000 3000 4000 5000 6000 7000 8000 f (Hz)
dB
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0 1000 2000 3000 4000 5000 6000 7000 8000 f (Hz)
0 1000 2000 3000 4000 5000 6000 7000 8000 f (Hz)
dB
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dB
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0 1000 2000 3000 4000 f (Hz)
0 1000 2000 3000 4000 f (Hz)
Input signal at 500 Hz (blue line)
with harmonics (red lines)
Signal pitched-shifted down
-1 octave to 250 Hz without
formant correction
Signal pitched-shifted down
-1 octave to 250 Hz with
preserved formants.
Signal pitched-shifted up
+1 octave to 1 kHz without
formant correction
Signal pitched-shifted up
+1 octave to 1 KHz with
preserved formants.
Input signal at 500 Hz (blue line)
with harmonics (red lines)