Joranalogue Audio Design’s Flow 3: Compact State-Variable Filter with a Self-Modulating Twist

Flow 3’s standout trick is its auto-dynamic capability, which lets the filter modulate its own cutoff frequency using a built-in decay generator and envelope follower. By sending a trigger to the dedicated input, users can activate the decay envelope, which then sweeps the filter frequency over a user-defined range. The range control is bipolar, so you can push the filter up or pull it down in response to each trigger, adding movement and punch to static sounds.

Alternatively, the envelope follower tracks the amplitude of incoming audio and translates it into a control voltage, which can also drive the filter’s cutoff. The two modulation sources—decay envelope and envelope follower—can be used independently or together, and their combined output is available at a dedicated envelope out. This opens up possibilities for dynamic, signal-reactive filtering without needing extra modules, keeping patches tidy and creative workflows flowing.

The video dives into Flow 3’s bread-and-butter filter sweeps, starting with a saw wave from Cycle 5 routed through the lowpass, bandpass, and highpass outputs. Each mode is demonstrated across a range of resonance settings, from subtle to full self-oscillation. Notably, the bandpass output requires a touch more resonance to match levels—a quirk familiar to filter aficionados.

Cranking the resonance brings Flow 3 into self-oscillation, where it produces clean, 10V peak-to-peak quadrature sine waves across its outputs. These sines are 90 degrees out of phase, making them ideal for stereo effects or as modulation sources. The filter tracks 1V/octave precisely, so it can double as a sine VCO or, with negative CV, as a quadrature LFO. Modulation inputs for frequency, resonance, and decay further expand its role as a flexible sound generator and modulator.

The built-in envelope follower isn’t just for modulating the filter—it can be used as a standalone CV extractor from any audio source. The video shows how sending audio into Flow 3 and monitoring the envelope output yields a control voltage that mirrors the input’s dynamics. The slew rate of this envelope can be adjusted for snappy or sluggish responses, and the resulting CV can be patched anywhere in your rack to modulate other modules.

Importantly, the envelope output remains available even when the range knob is set to zero, so you can extract envelopes without affecting the filter’s behaviour. This makes Flow 3 not only a filter and sound generator, but also a utility for dynamic modulation, opening up new avenues for creative patching and interaction within a Eurorack system.