01In plain English
Plugins add sounds and effects that the host software does not have: a synth, a reverb or a noise remover. VST is the most common format; Apple's AU format does the same job on Mac.
02How it works
Your audio program, called the host, handles recording and playback but ships with a limited set of sounds. A plugin is a small separate program that the host can load, so it appears inside the project. It might be a synthesizer that plays notes, a reverb that makes a vocal sound like it is in a hall, or a tool that removes background hiss. You open the plugin's window, turn its knobs, and the host feeds audio through it. Different makers sell or give away plugins, so you can build a collection over time. The format has to match: a plugin written for one format will not appear in a host that only supports another, like a plug that does not fit a socket.
03Why it matters when you are choosing
Plugins are how producers and editors build their sound. An app that cannot load the formats you already own means buying again or doing without.
04What to check
Check which formats the app supports (VST3, AU, AAX) and whether your existing plugins run on your operating system.
05Where you will meet it
06Common questions
What is the difference between VST and VST3?
VST3 is the later version of the format and fixes some limits of the older one, such as processing only when there is sound. Many hosts support both. If a plugin comes in VST3, use it, since the older version is gradually being dropped.
Do VST plugins work on Mac?
VST3 plugins do, if the maker offers a Mac version. Many Mac hosts also use the AU format, which is Apple's own. Check that the plugin and your host support the same format and that the plugin is built for your type of computer chip.
Are VST plugins free?
Many are, and many cost money. There are free synths and effects of good quality, alongside paid collections from major makers. Free plugins are a good way to learn, but check the license if you plan to release or sell music made with them.