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If speech containing voiced and unvoiced sounds is used as a vocoder’s analysis signal,
but the synthesis engine doesn’t differentiate between voiced and unvoiced sounds, the
result will sound rather weak. To avoid this problem, the synthesis section of the vocoder
must produce different sounds for the voiced and unvoiced parts of the signal.
The EVOC 20 TrackOscillator includes an Unvoiced/Voiced detector for this specific purpose.
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.
• Sensitivity knob: Determines how responsive U/V detection is. When this knob is turned
to the right, 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—determined by the Mode menu, as described in “Mode menu”
below—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.
• Mode menu: Sets the sound sources that can be used to replace the unvoiced content
of the input signal. You can choose between the following:
• Noise: Uses noise alone for the unvoiced portions of the sound.
• Noise + Synth: Uses noise and the synthesizer for the unvoiced portions of the sound.
• Blend: Uses the analysis signal after it has passed through a highpass filter for the
unvoiced portions of the sound. The Sensitivity parameter has no effect when this
setting is used.
• Level knob: Controls the volume of the signal used to replace the unvoiced content of
the input signal.
112 Chapter 6 Filter Effects