The Cherry Audio Rackmode String Filter comprises 36 high-Q parallel bandpass filters arrayed throughout the musical range (say that five times fast... go ahead, we'll wait). The original unit was intended to mimic the multiple static resonances of a stringed instrument body such as the violin or cello. When simple waveforms (especially solo waveforms) are played through it, the String Filter imparts a woody richness to the sound making it sound more "stringlistic."
Having so many resonant filters close together has a secondary effect on the amplitude of moving harmonics as well. If vibrato is applied (i.e., frequency modulation), some harmonics will ride up and down their nearby filter slopes creating amplitude modulation of that harmonic. It is this kind of detail that the unit was created for, but it can create interesting effects from many signal sources.
The adjustment of this mix has a profound effect on the resulting tone. The filters are arranged into odd and even interleaving sets which are associated with the left and right stereo outputs. The stark stereo spread of the odd/even splitting can be lessened by setting the Width control more toward Mono. Note that the String Filter is really useful for stereoizing mono sources.
Input Level- Sets the overall level of the incoming signal.
Frequency Offset- The filter frequencies of the original unit were fixed, but we've added a Frequency Offset knob that simultaneously adjusts the frequencies of all 36 filters in parallel.
Resonance Offset- Globally adjusts the bandwidth of all 36 filters. Turning this down all the way pretty much renders the effect inaudible (not at all stringy), and turning it up all the way will sound clangy and metallic.
Filter Frequency Levels- The 36 filters are divided into four groups of nine: Lo, Lo-Mid, Hi-Mid, and Hi. The four groups are mixed via their respective Filter Frequency Level controls. The adjustment of this mix has a profound effect on the resulting tone.
AM Sweep and Sync switch- AM Sweep is comprised of four asynchronously running LFOs which produce tremelo on each of the four frequency groups. Very different tremulant effects are available at different rate settings. When the Sync switch is enabled, the LFO is locked to the host DAW host tempo and the knob will snap to settings ranging from 8 beats up to 1/64th note triplets. With Sync enabled, the LFO's are no longer asynchronous and will move in lock stop.
FM Sweep and Sync switch- FM Sweep is comprised of four asynchronously running LFOs that modulate the frequencies of each of the four frequency groups. When the Sync switch is enabled, the LFO is locked to the host DAW host tempo and the knob will snap to settings ranging from 8 beats up to 1/64th note triplets. With Sync enabled, the LFO's are no longer asynchronous and will move in lock stop.
Width- Sets the stereo panning width of the filters.
Status- Enables and disables the String Filter.