Audio Unit

Audio Units arrived with Mac OS X in the early 2000s and do the same job as Steinberg's VST: an interface that lets a third-party compressor or synth run inside a host. The difference is that the format is part of the operating system. Apple ships its own units for EQ, reverb and resampling, and the auval tool validates that a plugin behaves before a host dares load it.

Apple's own DAW, Logic Pro, accepts nothing but Audio Units, which is why virtually every commercial developer ships each product in at least two formats. AUv3, introduced with iOS 9 in 2015, runs the plugin as an app extension in its own sandbox — a crashing effect no longer takes the whole session down with it, and iPad music suddenly became a market of its own.