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Chapter 6 Filter eects 12 6
EVOC 20 TrackOscillator
EVOC 20 TrackOscillator overview
EVOC 20 TrackOscillator is a vocoder with a monophonic pitch tracking oscillator. The tracking
oscillator tracks, or follows, the pitch of a monophonic input signal. If the input signal is a
sung vocal melody, the individual note pitches are tracked and mirrored, or played, by the
synthesis engine.
EVOC 20 TrackOscillator features two formant lter banks, an analysis bank, and a synthesis lter
bank. Each oers multiple input options.
You can capture an analysis signal source by using the audio arriving at the input of the channel
strip that EVOC 20 TrackOscillator is inserted into or by using a side-chained signal from another
channel strip.
The synthesis source can be derived from the audio input of the channel strip that EVOC 20
TrackOscillator is inserted into, a side chain signal, or the tracking oscillator.
Because you can select both the analysis and synthesis input signals, EVOC 20 TrackOscillator
is not limited to pitch tracking eects; you can also use it for unusual lter eects. For example,
you could lter an orchestral recording on one channel strip with train noises side-chained from
another channel strip. Or you could use it to process drum loops with side-chained signals, such
as other drum loops or rhythmic guitar, clavinet, and piano parts.
Vocoder overview
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 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 lms—such as
with the Cylons in Battlestar Galactica, and most famously, with the voice of Darth Vader from the
Star Wars saga.
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 lter banks.
Bandpass lters 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 lter banks are named the analysis and synthesis banks. Each lter
bank has a matching number of corresponding bands—if the analysis lter bank has ve bands
(1, 2, 3, 4, and 5), there will be a corresponding set of ve bands in the synthesis lter 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 lter bank, where it is
divided into bands.