3

Chapter 6 Filter eects 124
EVOC 20 TrackOscillator U/V detection parameters
Human speech consists of a series of voiced sounds—tonal sounds or formants—and unvoiced
sounds. The main distinction between voiced and unvoiced sounds is that voiced sounds
are produced by an oscillation of the vocal cords, whereas unvoiced sounds are produced by
blocking and restricting the air ow with lips, tongue, palate, throat, and larynx.
If speech containing voiced and unvoiced sounds is used as a vocoder’s analysis signal but the
synthesis engine doesn’t dierentiate between voiced and unvoiced sounds, the result sounds
rather weak. To avoid this problem, the synthesis section of the vocoder must produce dierent
sounds for the voiced and unvoiced parts of the signal.
EVOC 20 TrackOscillator includes an Unvoiced/Voiced detector. This unit detects the unvoiced
portions of the sound in the analysis signal and then substitutes the corresponding portions
in the synthesis signal with noise, with a mixture of noise and synthesizer signal, or with the
original signal. If the U/V Detector detects voiced parts, it passes this information to the synthesis
section, which uses the normal synthesis signal for these portions.
A short introduction to formants
A formant is a peak in the frequency spectrum of a sound. In the context of human voices,
formants are the key component that enables humans to distinguish between dierent vowel
sounds—based purely on the frequency of the sounds. Formants in human speech and singing
are produced by the vocal tract, with most vowel sounds containing four or more formants.
U/V detection parameters
•
Sensitivity knob: Rotate to determine how responsive U/V detection is. Turn to the right for
higher settings, where more of the individual unvoiced portions of the input signal are
recognized. When high settings are used, the increased sensitivity to unvoiced signals can
lead to the U/V sound source being used on the majority of the input signal, including voiced
signals. Sonically, this results in a sound that resembles a radio signal that is breaking up and
contains a lot of static, or noise. (The U/V sound source is determined by the Mode menu, as
described below.)
•
Mode menu: Choose the sound sources used to replace the unvoiced content of the
input signal.
•
Noise: Uses noise alone for the unvoiced portions of the sound.
•
N + Syn (Noise + Synthesizer): Uses noise and the synthesizer for the unvoiced portions of
the sound.