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• EVOC 20 PolySynth Modulation Parameters (p. 154)
• EVOC 20 PolySynth Output Parameters (p. 155)
• Getting the Best Results with the EVOC 20 PolySynth (p. 156)
• A Brief Vocoder History (p. 158)
• EVOC20 Block Diagram (p. 161)
What Is a Vocoder?
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 the synthesizer’s
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’ll
probably know it from tracks such as “O Superman” by Laurie Anderson, “Funky Town”
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. Also see A Brief 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.
How Does a Vocoder Work?
The speech analyzer and synthesizer features of a vocoder are actually two bandpass filter
banks. Bandpass filters allow a frequency band—a slice in the overall frequency
spectrum—to pass through unchanged, and cut the frequencies that fall outside the
band’s range.
In the EVOC 20 plug-ins, these filter banks are named the Analysis and Synthesis sections.
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 will be 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.
140 Chapter 7 EVOC 20 PolySynth