VST3, AU, AAX and CLAP: synth plugin formats explained
The same software synth often ships in four formats. VST3, AU, AAX and CLAP do not sound different: they are how the instrument plugs into your host.
Run a software synth installer and you will usually see a list of boxes to tick: VST3, AU, AAX, sometimes CLAP. They are not better or worse versions of the instrument. They are connection formats, like different plugs: the sound is identical, and your host decides which one it accepts.
Four formats, four origins
VST3: the most widespread
VST (Virtual Studio Technology) is Steinberg’s interface for running software instruments and effects inside a DAW. VST3, the third generation, is what developers ship today. Steinberg publishes the documentation and SDK on its VST 3 developer portal.
AU: Apple’s format
Audio Units is Apple’s plugin format, built into the operating system. On a Mac, it is the format Apple’s own music software expects, and most developers ship it alongside VST3.
AAX: the Pro Tools format
AAX is Avid’s format. According to Avid’s documentation, it covers effects and virtual instruments for Pro Tools, as well as the VENUE S6L live console and Media Composer. If Pro Tools is your main DAW, this is the one to install.
CLAP: the open format
CLAP (CLever Audio Plug-in) is the newest. Started by Bitwig and u-he, with contributions from commercial and open-source developers, it is released under the MIT licence, so any developer can implement it without signing an agreement. The official CLAP website tracks compatible hosts and plugins.
Which one should you install?
| Your setup | Format |
|---|---|
| Pro Tools | AAX |
| Apple music software on a Mac | AU |
| Most other DAWs, Windows or Mac | VST3 |
| A CLAP-capable host | CLAP, if the developer offers it |
When in doubt, install only what your host uses: extra formats slow down plugin scans and clutter your menus with duplicates.
A real-world example: Surge XT
Surge XT, an open-source hybrid synth maintained by a community of developers, shows where things stand today. It ships as VST3, AU on macOS, CLAP and LV2 on Linux, and runs on Windows, macOS and Linux. Under the hood are 12 oscillator algorithms, from classic subtractive to FM and wavetable. It is free, which makes it an excellent way to learn synthesis, and everything it teaches carries over to hardware synths, starting with envelopes. Formats and engines are listed on the Surge project site.
Mixing and processing your recorded tracks is a different craft, covered by our sister site digital-mixing.com.
My take
CLAP is the good news of recent years: an open format, no licence to negotiate, designed by people who build synths. Its future depends on host adoption rather than technical merit. For now the rule is pragmatic: install your host’s native format and ignore the rest. The format changes nothing about the sound; the time spent untangling duplicate plugins is another story.
