Low End Candy has released a free compressor plugin built specifically to teach compression, rather than just apply it.
Glassbox is a feed-forward, log-domain compressor using the gain computer and smooth decoupled peak detector described by Giannoulis, Massberg, and Reiss, chosen because its ballistics genuinely match textbook attack, release, ratio, and knee behavior rather than an emulation’s idiosyncratic response. The on-screen transfer curve is drawn by calling the same function the audio path uses, so what’s shown can’t drift from what’s heard.
Compression is a black box to most producers — you turn knobs, something changes, and you can’t tell whether it changed for the reason you think. Glassbox is the box you can see into: every number and shape on screen is measured from your own material while it plays, not asserted from a lookup table.
Glassbox features
- A SPLIT view showing before and after side by side on the same window and scale, with rust and teal shading marking where level was taken away or given back, and the detector level drawn live in white.
- Measured short-term LUFS, peak, crest, and gain reduction at three timescales, plus a WORKING % readout, with AUTO GAIN on by default for level-matched bypass comparisons.
- A live COACH that reports the most useful true statement about the current signal, plus hover tooltips explaining exactly what each control provably affects.
- A single transient view captured at full sample resolution with 30ms of pre-trigger, isolating exactly what attack and release are doing to a hit.
- 17 source recipes from kick to master bus, each with a gain-reduction target that a DIAL IT IN function matches against the actual incoming audio, plus nine deliberately wrong demo presets for comparison.
- Threshold to -60dB, ratio to 60:1, attack from 0.05-250ms, release from 5-2500ms with AUTO, quadratic soft knee, true lookahead, peak/RMS detection, and full sidechain and stereo linking controls.
Glassbox is available now as a free download for Windows and macOS in VST3 and AU plugin formats.
More information: Low End Candy
