User Guide

226 Chapter 15 EVOC 20 PolySynth
Gating Background Noises in the Analysis Signal
If the analysis signal is compressed, as recommended, the level of breath, rumble, and
background noises will rise. These background noises can cause the vocoder bands to
open, but this is normally not intended. In order to eliminate these noises, it’s therefore
a good idea to employ a noise gate before compression and treble boosting. If the
analysis signal is gated appropriately, you may find that you want to reduce the
Analysis Release value.
When gating speech and vocals, the Hysteresis parameter is important. Threshold
defines the level, above which the gate will open. Hysteresis defines a lower Threshold
level, under which the gate will close. The value is relative to the Threshold level.
The graphic above shows a Threshold setting, which is well-adapted to compressed
speech. Unwanted triggering by low or high frequency noise is avoided by the Noise
Gates’ dedicated sidechain filters. The Hold, Release, and Hysteresis values shown are
typical level envelopes, suitable for most vocal and speech signals.
Achieving the Best Analysis and Synthesis Signals
For good speech intelligibility, please keep these points in mind:
 The spectra of the analysis and synthesis signals should overlap almost completely.
Low male voices with synthesis signals in the treble range do not work well.
 The synthesis signal must be constantly sustained, without breaks. The track should
be played legato, as breaks in the synthesis signal will stop the vocoders output.
Alternatively, the Release parameter of the synthesis signal (not to be confused with
the Release time of the analysis section) can be set to a longer time. Nice effects can
also be achieved by the use of a reverberation signal as a synthesis signal. Note that
the two latter methods can lead to harmonic overlaps.
 Do not overdrive the vocoder. This can happen easily, and distortion will occur.
 Enunciate your speech clearly, if the recording is to be used as an analysis signal.
Spoken words, with a relatively low pitch, work better than sung vocals—even if the
creation of vocoder choirs is your goal! Pronounce consonants well. A nice example is
the rolled R of “We are the Robots,” by Kraftwerk, a classic vocoder track. This
pronunciation was specifically made to cater to the demands of the vocoder.