The BFS-1 is a VST emulation of the famous Bode frequency shifter.
The original unit was available as an expensive module for the Moog™ modular system.
The frequency shifter is not a pitch shifter, which changes frequencies by a multiplication. Instead, it shifts all frequencies/harmonics by adding a fixed amount. The sound reminds to a ring modulator, but unlike this, it is possible to get the upshifted and downshifted signal separately.
Unlike a ring modulator, the frequency shifter is also capable of changing the signal by a low amount, e.g. 1 Hz, to obtain effects known as “Barberpole flanging”.
This plugin has some additional features like delays for each section, an LFO (all host synced), an envelope with MIDI trigger and an envelope follower to modulate shift and/or volume.
Included is a version with a smaller GUI for laptops and an extra version with 2x oversampling.