EVOC 20 TrackOscillator Un/Voiced detection in Logic Pro for iPad
The Un/Voiced Detection section provides control over voiced and unvoiced sounds.
To explain, 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 flow with lips, tongue, palate, throat, and larynx.
If speech containing voiced and unvoiced sounds is used as a vocoder analysis signal but the synthesis engine doesn’t differentiate between voiced and unvoiced sounds, the result sounds rather weak. To avoid this problem, the synthesis engine of a vocoder must produce different sounds for the voiced and unvoiced parts of the signal.
EVOC 20 TrackOscillator includes an unvoiced/voiced detection circuit which identifies unvoiced elements of the sound in the analysis signal. Corresponding portions in the synthesis signal are then replaced with noise, with a mixture of noise and synthesizer signal, or with the original signal. If the U/V detection circuit identifies voiced parts, it passes this information to the synthesis section, which uses the normal synthesis signal for these portions.
About 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 different 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.
Un/Voiced Detection parameters
U/V Sensitivity knob and field: 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 U/V Src. pop-up menu.
U/V Source pop-up menu: Choose the sound sources used to replace the unvoiced content of the input signal.
Off: Do not replace unvoiced portions of the sound with a noise or synth signal.
Noise: Use noise alone for the unvoiced portions of the sound.
Noise + Synth: Use noise and the synthesizer for the unvoiced portions of the sound.
Blend: Use 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.
U/V Level slider and field: Set the volume of the signal used to replace the unvoiced content of the input signal.
Important: Be careful with the U/V Level control, particularly when using a high U/V Sensitivity value, to avoid internally overloading EVOC 20 TrackOscillator.
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