Kurzweil K2661 - LFO Sweep Filter; LFO Following Stereo 2 Pole Resonant Filter

KDFX Reference
KDFX Algorithm Specifications
10-153
902 LFO Sweep Filter
LFO following stereo 2 pole resonant filter
PAUs: 2
The LFO following filter is a stereo resonant filter with the resonant frequency controlled by an LFO (low-
frequency oscillator). The filter type is selectable and may be one of low pass (i), high pass (ii), band pass
(iii), or notch (iv) (see figure below).
Figure 10-69 Resonant Filters: (i) lowpass; (ii) highpass; (iii) bandpass; (iv) notch
The resonant frequency of the filter will sweep between the minimum frequency (Min Freq) and 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, though doing so will just invert the direction of the LFO. Meters
are provided to show the current resonance frequencies of the left and right channel filters.
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.
You can set the frequency of the LFO using the LFO Tempo and LFO Period controls. You can explicitly set
the tempo or use the system tempo from the sequencer (or MIDI clock). The LFO Period control sets the
period of the LFO (the time for one complete oscillation) in terms of the number of tempo beats per LFO
period. The LFO may be configured to one of a variety of wave shapes. Available shapes are Sine, Saw+,
Saw-, Pulse and Tri (Figure 2). Sine is simply a sinusoid waveform. Tri produces a triangular waveform,
and Pulse produces a series of square pulses where the pulse width can be adjusted with the “LFO
PlsWid” parameter. When pulse width is 50%, the signal is a square wave. The “LFO PlsWid” parameter is
only active when the Pulse waveform is selected. Saw+ and Saw- produce rising and falling sawtooth
waveforms. The Pulse and Saw waveforms have abrupt, discontinuous changes in amplitude which can
be smoothed. The pulse wave is implemented as a hard clipped sine wave, and, at 50% width, it turns into
(i) (ii)
(iii) (iv)