This video, via Synthesizers Reviews, takes a look at the Free State FX Son Of Storm Tide Flanger module for Dotcom-style 5U modular systems.

The module is based on an analog circuit designed by Jurgen Haible. It’s a mega-flanger design that offers some unique features:

• “Theta Processor” – The idea is to combine a delay line (Flanging) with all pass filters (Phasing), to get the huge number of peaks and notches, but a “musical” (notches per octave rather than notches per Hz) spacing as with Phasers. The 4 all pass filters have no big effect as long as the Flanger runs in mono, and they are certainly not enough to create the ideal of “musical” spacing of peaks described above. But as soon as you run it in stereo – BIG effect. Running the Flanger in stereo *without* the all pass filters is quite nice, but nothing really special; you have probably heard it many times before. But switching in the all pass filters sort of “unlocks” the stereo image.
• Thru Zero Flanging
• Noise Reduction compander inspired by the phaser in the ARP Quadra.
• Resonance – Resonance can be positive or negative (center zero potentiometer), and the resonance loop can be chosen short (one BBD) or long (both BBDs). This provides good variations, but is pretty standard. The interesting part is the Resonance Limiter, which is also “inside” the Compander system (after Compressor, before Expanders), inspired by ARP designs.
• Bounce – The summed control voltage (Manual, Pedal, LFO, Envelope follower) is fed into a sub audio BPF, then into a nonlinear amplifier with positive feedback, and then filtered by a second BPF. A variable portion of this is mixed to the straight CV to control the BBD’s clock frequency. The effect is most prominent on single-shot, non-periodic CV changes, such as a fast single Manual of Pedal sweep. The single sweep is followed by smooth “echoes” that go in either direction (faster clock and slower clock). This is to emulate the “bouncing” tape speed of reel-to-reel tape machines when the friction from a thump against the reel is suddenly released.
• Foldback –  This is a full wave rectifier in the CV path that prevents the clock frequency from going too low. Rather than just limiting the CV, it folds negative CVs back up, which gives a nice effect with the Bounce circuit and also with LFO waves that would go below zero (in combination with the manual CV,)
• LFO Waveshapes – a linear Triangle, and a EMS-like unsymmetrical Sine wave that produces the famous “roller coaster” or “Dive” effect.
• Anti-Aliasing Filter – Built around a single LM30

Pricing and Availability

The Son of Storm Tide Flanger is available for US $650 via Free State FX.