9

An envelope follower is coupled to each filter band. The envelope follower of each band
tracks, or follows, any volume changes in the audio source—or, more specifically, the
portion of the audio that has been allowed to pass by the associated bandpass filter. In
this way, the envelope follower of each band generates dynamic control signals.
Analysis
audio source
Synthesis
audio source
Analysis
filter bank
band 1–5
Synthesis
filter bank
band 1–5
Envelope
follower
1–5
VCA
1–5
Control signal 1–5
Audio output
U/V
detection
These control signals are then sent to the synthesis filter bank—where they control the
levels of the corresponding synthesis filter bands. This is done with voltage-controlled
amplifiers (VCAs) in analog vocoders. Volume changes to the bands in the analysis filter
bank are imposed on the matching bands in the synthesis filter bank. These filter level
changes are heard as a synthetic reproduction of the original input signal—or a mix of
the two filter bank signals.
The more bands a vocoder offers, the more precisely the original sound’s character will
be reproduced by the synthesis filter bank. The EVOC 20 PolySynth provides up to 20
bands per bank. See EVOC20 Block Diagram for a detailed image of the EVOC20 Polysynth
signal path.
Setting Up Your EVOC 20 PolySynth Host Application
To use of the EVOC 20 PolySynth, you need to insert it into the Instrument slot of an
instrument channel strip. You also need to provide an audio signal as the analysis audio
source, via a sidechain.
To set up the EVOC 20 PolySynth in your host application
1 Insert the EVOC 20 PolySynth into the Instrument slot of an instrument channel strip.
2 Choose an input source in the Side Chain menu in the plug-in header of the EVOC 20
PolySynth. This can be an audio track, live input, or bus, depending on the host application.
The EVOC 20 PolySynth is now ready to accept incoming MIDI data and has been assigned
to an input, audio track, or bus—via a side chain.
141Chapter 7 EVOC 20 PolySynth