The main purpose with the frequency shifter is to make frequency shift up and down for processed audio signal. Two signal sources are needed; the carrier and the audio. Both carrier and audio signals are splitted in two chains and are pre-processed to accomplish 90 degrees phase shift between splitted signals. 
The carrier generator has two frequency ranges; LF (low frequency) and AUDIO and it's controlled by knobs
COARSE, FINE and external CV signals (CARRIER CV). The carrier generators outputs are pure sine waveforms with 90 degrees delay between them. Outputs are patched to both ring modulators inputs. Two ring modulators (dual balanced multipliers) receives 0 and 90 degrees shifted carrier and audio signals . The outputs from the multipliers are combined in two ways; the frequency shift UP and DOWN.  The frequency shifted audio signal is a sum (UP) or difference (DOWN) of the carrier generators frequency (a pure sine waveform) and all audio signals frequencies (fundamentals and harmonics). The FSH-1 works in two modes; as frequency shifter and as dual ring modulator. A ring modulator is a classic audio effect device and due to the non-harmonic character of the output signal. It's very useful to create metallic timbres such as bells, sweeping whistles and percussive sounds and tremolo effects. The obvious effect (particularly in LF mode) is a stereo panning effect of audio signal.