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F_PHASR8 – 4/6/8-Stage Optical Phaser

F_PHASR8 is an analog-style phaser with an optical (lamp/LDR) modulation model and up to eight cascaded all-pass stages. It delivers classic sweeping notches with the smooth, organic motion characteristic of optical circuits.

Inputs / Outputs

  • IN L, IN R — Audio inputs. If only IN L is connected, the signal is duplicated to the right channel.
  • OUT L, OUT R — Stereo audio outputs.
  • MOD 1–4 — CV modulation inputs (−5 V…+5 V nominal), each freely assignable to a target parameter via its assign button.

Controls

  • RATE (0.01–5.00 Hz, default 0.50) — LFO speed that “drives the lamp”.
  • DEPTH (0.00–1.00, default 0.85) — Modulation depth applied to the sweep width.
  • CENTER (80–2000 Hz, default 500) — Mid frequency around which the notches sweep.
  • WIDTH (0.0–3.0 oct, default 2.0) — Sweep span in octaves.
  • FEEDBACK (−0.95…+0.95, default +0.50) — Feeds the wet signal back into the input for sharper, more resonant notches. Negative values flip the phase of the feedback and produce a different color.
  • MIX (0–1, default 0.50) — Dry/Wet blend.
  • OPT SLEW (5–800 ms, default 120 ms) — Optical response time (slew) of the virtual LDR. Higher values = slower, gooier motion; lower values = snappier response.
  • STAGES (4 / 6 / 8) — Number of all-pass stages. More stages → more notches and a deeper sweep.

Modulation System (MOD 1–4)

Each MOD input has an assign button with a dropdown menu. The available targets are:

OFF, Rate, Depth, Center, Width, Feedback, Mix, OptSpeed, Stages

  • OFF — Disables the selected MOD input.
  • Rate — CV adds/subtracts from LFO rate (approx. 1 V ≈ ±0.5 Hz; clamped to 0.01–5.00 Hz).
  • Depth — Bipolar depth modulation (1 V ≈ ±0.10; clamped 0.00–1.00).
  • Center — Musical mapping in octaves (1 V ≈ 0.2 oct ratio around the current CENTER; clamped 80–2000 Hz).
  • Width — Changes sweep span (1 V ≈ ±0.2 oct; clamped 0.0–3.0 oct).
  • Feedback — Modulates resonance character (1 V ≈ ±0.10; clamped −0.95…+0.95).
  • Mix — Dry/Wet modulation (1 V ≈ ±0.10; clamped 0–1).
  • OptSpeed — Changes optical slew time (1 V ≈ ±20 ms; clamped 5–800 ms).
  • Stages — CV-based switching between 4/6/8 stages using three zones (typical thresholds: CV ≤ −1.5 V → 4 stages; −1.5…+1.5 V → 6 stages; CV ≥ +1.5 V → 8 stages). If MOD CV is near 0 V, the front-panel STAGES switch determines the setting.

Panel Indicators

  • LAMP LED — Shows the internal optical lamp brightness (0–1) after slew. This visualizes the optical driver that controls the sweep, not audio level.

How It Works

  1. A sine LFO drives a virtual lamp, producing a 0–1 intensity signal.
  2. The lamp signal is passed through an exponential OPT SLEW stage to emulate the inertia of a real LDR (slow rise/fall).
  3. The slewed value maps logarithmically to the all-pass cutoff frequencies around CENTER with span WIDTH and amount DEPTH.
  4. Audio passes a cascade of 4/6/8 first-order all-pass stages (per channel), creating moving spectral notches when blended with the dry signal.
  5. FEEDBACK re-injects wet signal to increase resonance; MIX blends the result with the dry path.

Tips & Usage

  • For vintage glide, keep OPT SLEW around 80–200 ms; for modern snappiness, try 10–40 ms.
  • Small negative FEEDBACK values (−0.2…−0.4) give a different color that sits well in dense mixes.
  • CENTER ≈ 300–800 Hz is a sweet spot for classic guitar/keys; widen WIDTH for more movement.
  • Use 4 stages for subtle shimmer, 6 for a clear sweep, 8 for deep, liquid motion.
  • Assign MOD to Stages for rhythmic switching (e.g., a step sequencer around −2 V/0 V/+2 V for 4/6/8).
  • Envelope into Depth or Mix creates expressive “wah-like” accents.

Example Settings

  • Classic 4-Stage Swirl: Stages=4, Rate=0.40, Depth=0.70, Center=600, Width=1.2 oct, Feedback=+0.35, Mix=0.50, Opt Slew=120 ms.
  • Mix-Friendly 6-Stage: Stages=6, Rate=0.25, Depth=0.60, Center=450, Width=0.9 oct, Feedback=+0.25, Mix=0.40, Opt Slew=140 ms.
  • Deep 8-Stage Liquid: Stages=8, Rate=0.35, Depth=0.90, Center=500, Width=2.0 oct, Feedback=+0.55, Mix=0.55, Opt Slew=160 ms.
  • Subtle Movement: Stages=6, Rate=0.15, Depth=0.35, Center=700, Width=0.6 oct, Feedback=+0.10, Mix=0.30, Opt Slew=100 ms.
  • Snappy Wah-Like: Stages=4, Rate=2.00, Depth=1.00, Center=800, Width=1.5 oct, Feedback=+0.20, Mix=0.60, Opt Slew=20 ms.
  • Wide Slow Ocean: Stages=8, Rate=0.08, Depth=0.80, Center=400, Width=2.5 oct, Feedback=+0.45, Mix=0.50, Opt Slew=220 ms.
  • Negative-FB Color: Stages=6, Rate=0.50, Depth=0.75, Center=520, Width=1.8 oct, Feedback=−0.35, Mix=0.55, Opt Slew=130 ms.
  • Drum Bus Tuck-In: Stages=4, Rate=0.20, Depth=0.30, Center=350, Width=0.5 oct, Feedback=+0.10, Mix=0.25, Opt Slew=90 ms.
  • Ambient Pad Swim: Stages=8, Rate=0.12, Depth=0.85, Center=450, Width=2.2 oct, Feedback=+0.50, Mix=0.60, Opt Slew=200 ms.
  • Bass-Safe Glide: Stages=6, Rate=0.18, Depth=0.45, Center=300, Width=0.8 oct, Feedback=+0.15, Mix=0.35, Opt Slew=110 ms.

Troubleshooting

  • No movement? Increase DEPTH, reduce OPT SLEW, or raise RATE.
  • Too hollow or phasey? Reduce MIX or try fewer STAGES; adjust CENTER upward.
  • Harsh peaks? Lower FEEDBACK or try a small negative value.
  • Unintended stage flips? If MOD is assigned to Stages, center its CV near 0 V or set the target to OFF.

Notes

  • Mono input is duplicated to stereo if IN R is unused.
  • The LAMP LED reflects the slewed lamp value (0–1) and is not an audio meter.
  • Very slow rates (<0.05 Hz) can sound nearly static; increase DEPTH or WIDTH for stronger motion.