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KDFX Reference
KDFX Algorithm Specifications
901 TrigEnvelopeFilt
Triggered envelope following stereo 2 pole resonant filter
PAUs: 2
The triggered envelope following filter is used to produce a filter sweep when the input rises above a
trigger level. The triggered envelope following filter is a stereo resonant filter with the resonant frequency
controlled by a triggered envelope follower. The filter type is selectable and may be one of low pass (i),
high pass (ii), band pass (iii), or notch (iv).
Figure 10-67 Resonant Filters: (i) lowpass; (ii) highpass; (iii) bandpass; (iv) notch
The resonant frequency of the filter will remain at the minimum frequency (Min Freq) prior to being
triggered. On a trigger, the resonant frequency will sweep to the maximum frequency (Max Freq). The
minimum and maximum frequencies may be set to any combination of frequencies between 58 and 8372
Hz. Note that the terms minimum and maximum frequency are a reference to the resonant frequencies at
the minimum and maximum envelope levels; you may set either of the frequencies to be larger than the
other. A meter is provided to show the current resonance frequency of the filter.
The filter Resonance level may be adjusted. The resonance is expressed in decibels (dB) of gain at the
resonant frequency. Since 50 dB of gain is available, you will have to be careful with your gain stages to
avoid clipping.
When the input signal envelope rises above the trigger level, an envelope generator is started which has an
instant attack and exponential decay. The generated attack may be lengthened with the the smoothing
parameter. The smoothing parameter can also lengthen the generated decay if the smoothing rate is lower
than the decay. The generated envelope is then used to control the resonant frequency of the filter.
(i) (ii)
(iii) (iv)
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