Project
4Comp: AUv3 Compressor
Four compressors, four faces — FET, VCA, optical, and vari-mu
What it is
4Comp is an iOS AUv3 compressor with four selectable models: FET, VCA, Optical, and Vari-Mu. Each is its own DSP path — a feedback FET with all-buttons mode, a two-stage VCA bus compressor, an optical cell with level-dependent release, and a vari-mu stage whose ratio rises with level. Picking a model re-skins the whole interface, so the knobs, meters, and colours match the machine you are reaching for. Stereo link, sidechain high-pass, dry/wet, input and output gain with auto make-up, a VU-style gain-reduction needle, and factory presets round it out, with real-time-safe DSP and zero sample latency by default.
Who it’s for
Producers and engineers on iPhone and iPad who want four classic compressor characters — drum-bus FET, bus-glue VCA, vocal optical, and mastering vari-mu — in a single AUv3 plugin.
Features
Four compressor models
FET, VCA, Optical, and Vari-Mu in one plugin, each with the interface and colour of the hardware it models.
FET — fast feedback
Fast gain reduction from a feedback detector, with an all-buttons mode for hi-hats, drum buses, and spiky guitars.
VCA — bus glue
Program-dependent auto release that tames transients and spikes without grabbing.
Optical — level-dependent release
Smooth release from a modelled photocell, with the cell's light memory, suited to vocals, brass, and strings.
Vari-Mu — rising ratio
A ratio that rises with level, plus harmonic colour that thickens thin tracks on a mix bus.
Four DSP paths, not presets
Each model is its own compressor engine — feedback FET, two-stage VCA, photocell release, and rising-ratio tube — and switching animates to the new model's look.
Sidechain high-pass and stereo link
Filter the detection sidechain, and choose linked or dual-mono operation across the stereo field.
Mix, gain, and metering
Dry/wet mix, input and output gain with auto make-up, and a VU-style gain-reduction needle keep the gain stage visible.
Fully accessible
VoiceOver labels the model picker, every knob, the toggles, and the meters, and knobs are adjustable.
Tech
- Swift
- SwiftUI
- C++ DSP kernel
- AUv3 extension architecture
- Real-time audio
- AU parameter automation
- iPhone & iPad
- iOS 16+
Four compressors, one plugin
4Comp puts four classic compressor topologies in a single AUv3 effect. Each model is a separate DSP path rather than a preset over one circuit — a feedback FET, a two-stage VCA, a modelled photocell, and a rising-ratio tube stage. Picking a model re-skins the interface to match that hardware's colours, so the plugin feels like the machine you're reaching for, and switching faceplates mid-session animates to the new look.
The four models
FET — fast gain reduction from a feedback detector, with an all-buttons mode. Hi-hats, drum buses, spiky guitars.
VCA — bus glue with program-dependent auto release. Tames transients and spikes without grabbing.
Optical — smooth, level-dependent release from a modelled photocell and its light memory. Vocals, brass, strings.
Vari-Mu — a ratio that rises with level, plus harmonic colour that thickens thin tracks. Mix bus and mastering.
Shared controls
Every model shares the same complement: stereo link (linked or dual mono), a sidechain high-pass filter, dry/wet mix, input and output gain with auto make-up, and a VU-style gain-reduction needle. Seventeen factory presets give you a starting point, and parameters can be automated in hosts that support it.
Real-time DSP
The compressor runs as a C++ DSP kernel on the audio render thread with the host's real-time priority, with zero sample latency by default. Parameter changes are smoothed, and switching models is glitch-free.
Accessible by design
VoiceOver labels the model picker, every knob, the toggles, and the meters. Knobs are adjustable and announce their values, so the full compressor is usable without seeing the screen.