These days, most plugins come in both AU and VST format, and Macintosh (at least up to OSX) continues to support both formats.
When installing on a Mac, many users go with the default AU version all the time. But, does it matter? In fact, due to the way AU and VST plugins behave the answer is sometimes yes. Let’s examine why and when it matters.
MIDI OUT – VST vs. AU
VST plugins handle MIDI output very differently than AU plugins. More specifically, VST plugins have the capability of sending out MIDI signals (if they are programmed to do so by the plugin designer) and AU plugins do not. (At least that’s my experience)
This is WHY it does make a difference which version you choose.
TO TRIGGER OR NOT TO TRIGGER?
That is the question! If you can imagine an instance in which you would like to have your plugin act like a traditional external hardware instrument and be able to transmit a signal out, you should choose the VST version. This is WHEN it matters what type of plugin format you choose.
Think about the types of instruments that would traditionally have this capability – drum machines, synths & certain types of effects modules that use MIDI triggers (like arpeggiators or chord generators) quickly come to mind.
So, when installing plugins like this, ask yourself a quick question: do I want to be able to trigger other devices with the output of this plugin? If the answer is yes, and the plugin includes a VST version that is capable of transmitting MIDI, install it.
One prime example of just how much better VST use can be over an AU version is Plugin Boutique’s excellent Scaler plugin. When using the AU version, you are not able to trigger external plugins with it. This means that when you find a selection of chords you like, you have to manually drag the MIDI files into a channel you want to trigger and then manually edit the length of your chords to play a pattern.
With the VST version, you can just set it to trigger an external plugin and whatever you play is recorded, as you played it, into the external plugin track. This video demonstrates the process:
In the end, it all depends on what you want from a plugin. From my perspective, VST still has some unique advantages.