It's always a pleasure to find a plug-in that does one job, does it well, and makes it easy. Fazortan (about $42) from Polish software developer d16 Group (d16.pl) is a cross-platform AU and VST effects plug-in devoted solely to flanging and phasing. It is a true stereo effect; the right and left channels are processed separately, and a Stereo Phase knob lets you offset the phases of the LFOs affecting each channel by as much as 180 degrees. Among other things, you can use that to add stereo depth to a mono input (see Web Clip 1).
Audio entering Fazortan is passed through a notch filter with two, four, six, or eight notches. You use the Feedback knob to enhance the filter's effect by accentuating its peaks and notches. The dry/wet knob determines the mix of the filtered and unprocessed signal, and the Output Volume knob and associated LED meters let you set the output level. For motion, you get two multiwaveform LFOs whose signals are mixed to modulate the notch filter's frequency. The notches are spread evenly across the frequency spectrum from 5 Hz to 20 kHz, and the LFOs shift all notches equally. The LFO frequencies, depths, and waveforms are completely independent, and you can add a DC offset to the amplitude of the first LFO. That gives you a lot more waveshape flexibility when the LFOs are mixed.
Although Fazortan produces the usual whooshing and whirring effects associated with phasing and flanging, it also offers very subtle sweetening. The audio quality is excellent, and it can make an otherwise dull track stand out without taking over (see Web Clip 2). The 28 factory presets cover the basics, and you can save your own presets and preset banks using a categorized browser. Fazortan's MIDI Learn implementation lets you latch any control to any MIDI continuous controller, and you can save MIDI controller maps. Phaser/flanger plug-ins are common, but Fazortan's price and sound quality make it worth checking out.