ZL Audio ZL Compressor

ZL Compressor by ZL Audio is the most feature-packed freeware compressor, with a control set that looks more like a paid mastering plugin than a freebie. Four operating modes cover most compression flavors. Clean is a transparent VCA-style mode. Classic is a feedback FET response with edge and bite. Optical is a smooth opto behavior closer to LA-2A territory. Lastly, Vocal is purpose-tuned for vocal dynamics and works well as the default for the vocal channel.

On top of mode selection, you get threshold, ratio, attack, release, makeup, knee, and curve controls, plus Pump and Smooth knobs that reshape the attack and release behavior beyond standard timing. For me, the standout feature is the 8-band sidechain EQ. You can shape what the detector hears band by band, with an interactive spectrum display, which is a level of sidechain control most paid compressors don’t offer. Oversampling runs up to 8x.

It is useful for bouncing, but the manual specifically warns against automating it because it can cause clicks and shift latency mid-playback. There’s also a lookahead control for catching tight transients. The plugin is open-source under AGPLv3, and the installers cover macOS, Windows, and Linux on x86-64 and ARM64.