The Shape of Waves.In a traditional vibe circuit an LFO sends a regularly-varying voltage to an internal lamp, whose brightness changes the resistance of the light-dependent resistors that set the center frequencies of the phasing filters (say that ten times fast!). The bias setting determines the brightness of the lamp when the LFO’s amplitude/intensity is set to zero. In other words, the bias sets the center point around which the LFO wiggles! There are a ton of variables in the system: for example, even if the LFO generates a perfectly symmetrical waveform, the lamp may still have different rise and fall times. Also, a lightbulb does not turn on or off instantly—there is a lag that becomes more noticeable at higher speed settings, and speed affects intensity in the circuit. All these interdependencies and more have been accounted for in UltraViolet and exploited for your benefit!At the Mid bias setting the LFO waveshape is sinewave-like, but the different rise and fall times of the lamp result in the lurching, lopsided and wooshy warble at the heart of the beloved vibe sound. At the High bias setting, the LFO shape is optimized for a smoother and more symmetrical result that gets you further into phaser territory in Chorus and Blend Modes, with higher frequencies being swept through. At the Low bias setting, the LFO waveform is more squarish (but still smoothed by lamp lag), sweeping lower frequencies and lending itself to phase tremolo effects in Chorus or Blend Modes, or yielding somewhat more steady pitch (with a dramatic lump) in Vibrato Mode.
