It is okay to use other instruments (real or virtual) to put the featured plugin in context. The featured plugin must be easily identifiable and not hidden in the mix or masked by other instruments throughout the demo. One good approach is to use the featured plugin on its own at the beginning of the track and add more instruments later in the piece.
You should avoid using other instruments that are similar to the featured plugin. For example don’t use another flute library if you are writing a demo for a flute plugin.
Demos should be around two minutes or less and only as long as necessary. A good 30 second track will likely be placed higher in the playlist than a repetitive 2 minute track.
The goal is to introduce the listener to the plugin and to show it in its most useful contexts. You need to get the listener’s attention in the first few bars to prevent them skipping your track or moving on to a different plugin.
The use of effects should be limited and should only be used to add polish to your demo. Effects should not be used in a way that significantly alters the sound of the featured plugin.
Demos should be delivered as 24bit 48Khz wav files.
Don’t deliver a highly compressed or super-loud track. Try to have a good dynamic range. I’ll master all of the demos together to keep a consistent volume across the playlist and if your track is too loud its volume will be reduced.
The order of the playlist is determined by how well the demo sells the plugin. I also organise the playlist to avoid two similar sounding tracks being played one after another.