10.6

305Logic Pro Instruments
4. Adjust the volume levels of EVOC 20 PolySynth and the side chain source—if not
muted—to meet your needs.
5. To further enhance the sound, adjust the knobs, sliders, and other controls, and insert
other effect plug-ins.
Vocoder basics
The word vocoder is an abbreviation for voice encoder. A vocoder analyzes and transfers
the sonic character of the audio signal arriving at its analysis input to synthesizer sound
generators. The result of this process is heard at the output of the vocoder.
The classic vocoder sound uses speech as the analysis signal and a synthesizer sound as
the synthesis signal. This sound was popularized in the late 1970s and early 1980s. You
may be familiar with tracks such as “O Superman” by Laurie Anderson, “Funkytown” by
Lipps Inc., and numerous Kraftwerk pieces—such as “Autobahn,” “Europe Endless,” “The
Robots,” and “Computer World.”
In addition to these “singing robot” sounds, vocoding has also been used in many films—
such as with the Cylons in Battlestar Galactica, and most famously, with the voice of Darth
Vader from the Star Wars saga. See Vocoder history.
Vocoding, as a process, is not strictly limited to vocal performances. You could use a drum
loop as the analysis signal to shape a string ensemble sound arriving at the synthesis input.
The speech analyzer and synthesizer features of a vocoder are two bandpass filter banks.
Bandpass filters allow a frequency band—a slice in the overall frequency spectrum—to pass
through unchanged. Frequencies that fall outside the band are cut.
In the EVOC20 plug-ins, these filter banks are named the analysis and synthesis banks.
Each filter bank has a matching number of corresponding bands—if the analysis filter bank
has five bands (1, 2, 3, 4, and 5), there is a corresponding set of five bands in the synthesis
filter bank. Band 1 in the analysis bank is matched to band 1 in the synthesis bank, band 2
to band 2, and so on.
The audio signal arriving at the analysis input passes through the analysis filter bank,
where it is divided into bands.
An envelope follower is coupled to each filter band. The envelope follower of each band
tracks, or follows, 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.