A two-channel JFET limiter / compressor built as a component-level circuit model: the whole audio board — input followers, gain stage, the JFET-controlled stage, the precision rectifier, the attack / release network, the RATIO divider and the balanced output driver — is solved as a circuit in real time. Free download.
Not a compressor algorithm: the circuit is solved node by node at sample rate, as seven small stages in signal order — op-amps with real bandwidth, slew rate and offsets, diodes and FET with their tolerances (the two channels differ slightly, as two real boards do). Turning a knob moves the potentiometer inside the simulated board; the knee, the slope and the timing fall out of the components.
One junction FET as a shunt in the feedback of the controlled stage takes up to 17 dB out of the loop. A hard knee, a steep slope above the threshold and the gentle second-harmonic colour of a FET doing real work — that is the sound of the circuit.
A precision full-wave rectifier listens to the output and drives a diode-steered attack / release network: ATTACK 0.2–25 ms, RELEASE 50–750 ms, as printed on the scales. RATIO 3:1 … 10:1 sets the control-voltage offset, so it moves the threshold (−15 … −9 dBFS) as much as the slope.
GAIN 0 … +22 dB sits before the controlled stage and drives the programme into the threshold; OUTPUT −8 … 0 dB brings the level back. Calibrated at 0 dBFS = 4.4 V peak.
Two independent boards with their own controls. The ON / OFF switch is LINK: channel 2 follows channel 1 for stereo; switch it off for dual mono.
An aux Sidechain input in both layouts. Switch the detector from the board's own output to the key (right-click → Detector) and the loop becomes feed-forward from the key.
Red LIMIT lights while the channel is reducing gain; green GAIN is the overload indicator of the input amplifier — when it flickers, turn GAIN down.
The noise floor of the input stage and the amplifiers is part of the model (about −104 dBFS, switchable). A saturating output transformer stage — core hysteresis solved sample by sample — is available as an option for low-frequency weight and harmonics.
A screen-printed rack panel; hover to read a value, double-click to reset, window sizes from 0.77× to 2×. Oversampling 1× / 2× / 4× for fast gain changes on bright material; at 1× the integration warping is compensated so the response follows the circuit to 20 kHz.
Linux: unzip into ~/.clap/ or ~/.vst3/.
Windows: into %COMMONPROGRAMFILES%\CLAP\ or %COMMONPROGRAMFILES%\VST3\.
Then rescan plugins. Stereo (2/2 + stereo sidechain) and mono (1/1 + mono sidechain) layouts.
Manual (PDF) —
every control, its range, levels, LINK, sidechain, oversampling and the signal path.
A complete channel strip built from circuit models: a five-band parametric EQ with a full VCA dynamics row — noise gate, downward expander and a soft-knee compressor/limiter — plus an opto input limiter in front of it all. Free download.
Every section is a component-level model of a real analogue circuit, solved from the schematic: the EQ filters are computed node by node, the compressor's soft knee falls out of a diode's exponential I/V characteristic sitting in its control path, and the gate closes with a constant-slope ramp because that is exactly what a constant current source pulling on a timing capacitor does. Turning a knob does not switch a digital filter; it moves the potentiometer inside the simulated circuit. Where analogue behaviour has a shape, that shape is in the model — not drawn in afterwards.
A comparator gate, not a soft one: opens near-instantly so transients never get clipped, holds open for 0–2 s with retrigger, then closes with a constant-rate ramp of 10–500 dB/s. Threshold −25…+5 dBu, sidechain key input, MIX as gate depth.
The compressor circuit with its control path mirrored — below the threshold the gain falls away with the same soft knee. Ratio 1:1…1:3.94, RANGE caps the floor at 0–60 dB. For bleed and hiss without chopping decay tails.
Each band sweeps 10 Hz–21 kHz in three ranges (×0.1 / ×1 / ×10), gain ±18 dB, FRQ/WIDE bandwidth. State-variable filters with centre-tapped gain pots — the airy top end of the real hardware. Sweepable HP 10–250 Hz and LP 3–41 kHz.
RMS-detected, feed-forward VCA compressor with a genuinely soft knee and the fixed, program-friendly time behaviour of its analogue control path. Ratios 1:1 to a 51:1 brick, ±18.5 dB make-up, sidechain, MIX for parallel compression.
GAIN ±20 dB and a Vactrol limiter with CEIL −24…0 dBFS in front of the whole chain, catching peaks before the strip sees them — timing from the VTL5C3 datasheet.
Below 100 % the dry signal dilutes the processed one: for the gate that is the depth of the cut, for the expander the floor, for the compressor plain parallel compression. Gate, expander and compressor are each switchable OFF / PRE / POST the EQ.
Two channels from one set of controls with LINK, or dual mono — switch the panel to L or R and edit each side on its own. The whole path runs in an oversampled block (1× / 2× / 4×) so fast gain changes don't fold back into the audible band.
A 19″ 2U drawing, screen-printed like the real thing; everything that moves is drawn live over it. Hover to read a value, double-click to reset, SCALE 1–5 picks the window size. Portable presets hold the whole strip.
Linux: unzip into ~/.clap/ or ~/.vst3/.
Windows: into %COMMONPROGRAMFILES%\CLAP\ or %COMMONPROGRAMFILES%\VST3\.
Then rescan plugins. Tested in Bitwig, Ableton Live and Cubase. GPL-3.0 — free and open source.
Every control, its range and what the circuit behind it does — input stage, gate, expander, EQ, compressor, presets and the signal path. Download the PDF.
The PEQ15 equaliser and the AKL 634 / 636 dynamics were published as DIY studio constructions by Alan Kraus in Amatérské radio (2001–2006). LAP PEQ15 models the complete instruments from their schematics; stereo is two of them side by side.
In the works. More when it's ready.
In the works. More when it's ready.