Spectroscope

What it is

Six analysis instruments on one screen, built with JUCE 8 and shipped three ways from one codebase: an Audio Unit, a VST3, and a standalone macOS app. In a DAW it shows whatever audio reaches that point in the chain and passes it on unchanged; standalone, it listens to an input device, which is how you look at audio a DAW never touches. Each instrument can be switched off, and one that isn’t lit does no work.

What was hard

The audio thread can’t allocate, lock, or wait, so processBlock does one copy into a preallocated lock-free ring and returns, and a separate analysis thread does the FFTs, loudness, and correlation — when that thread falls behind, the dropped blocks are counted and shown in the header rather than smoothed over. The other hard part was making the measurements trustworthy: the loudness meter follows BS.1770, so the tests assert against known references (a −18 dBFS 997 Hz sine has to read −15.0 LUFS integrated), and CI runs those DSP tests along with Apple’s auval and pluginval on every build, because a meter that is quietly wrong is worse than no meter.