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Chapter 6 Filter eects 12 7
An envelope follower is coupled to each lter band. The envelope follower of each band tracks,
or follows, volume changes in the audio source—or, more specically, the portion of the audio
that has been allowed to pass by the associated bandpass lter. In this way, the envelope
follower of each band generates dynamic control signals.
These control signals are then sent to the synthesis lter bank—where they control the levels of
the corresponding synthesis lter bands. This is done with voltage-controlled ampliers (VCAs)
in analog vocoders. Volume changes to the bands in the analysis lter bank are imposed on the
matching bands in the synthesis lter bank. These lter level changes are heard as a synthetic
reproduction of the original input signal—or a mix of the two lter bank signals.
EVOC 20 TrackOscillator interface
EVOC 20 TrackOscillator is divided into a number of parameter sections.
LFO
parameters
Analysis In parameters
U/V Detection
parameters
Formant Filter parameters
Output
parameters
Synthesis In parameters
Tracking Oscillator
parameters
•
Analysis In parameters: Determine how the input signal is analyzed and used by the analysis
lter bank. See EVOC 20 TrackOscillator analysis in parameters on page 128 .
•
U/V Detection parameters: Detect the unvoiced portions of the sound in the analysis signal,
improving speech intelligibility. See EVOC 20 TrackOscillator U/V detection parameters on
page 129.
•
Synthesis In parameters: Determine how the input signal is used by the synthesis lter bank.
See EVOC 20 TrackOscillator synthesis in parameters on page 131.
•
Tracking Oscillator parameters: Determine how the analysis input signal is used by the oscillator.
See Tracking oscillator parameters on page 131.
•
Formant Filter parameters: Congure the analysis and synthesis lter banks. See EVOC 20
TrackOscillator formant lter on page 133.
•
LFO parameters: Modulate either the oscillator pitch or the Formant Shift parameter. See
EVOC 20 TrackOscillator modulation on page 134 .
•
Output parameters: Congure the output signal of the EVOC 20 TrackOscillator. See EVOC 20
TrackOscillator output parameters on page 135.