Some effects (reverb being the best example) are often used as send effects rather than as track insert effects. This allows (for example) one reverb (hardware or software) to be used for the entire project (or session, to use Qtractor terminology). I explored how to use send effects in Qtractor.
I was surprised to find that there’s currently no way to use a plugin as a send effect from within Qtractor. However, an external effect program can be used as a send effect, and a plugin can be run as a standalone external program and so be used as a send effect that way.
For my test I used Calf Reverb. I started JACK and opened a Qtractor session. I then launched Calf Plugin Pack for JACK (calfjackhost) from the menu. From its Add plugin menu I chose Reverb. I clicked the Reverb button to open Calf Reverb’s user interface. I set Dry Amount to its minimum setting and increased Wet Amount to 0.0 dB. (Send effects are normally set to be fully “wet”.)
In Qtractor, I chose a track named “Melody” to apply reverb to. I right-clicked in the track’s plugin inset area, but instead of choosing Add Plugin… I chose Inserts > Add Insert. This opened an Insert window. I set the Dry / Wet control to 1.000.
I clicked the Active button in the Insert window, soloed the “Melody” track in Qtractor, and played the track. It now had reverb applied. I adjusted the reverb amount by turning down the Send Gain in the Insert window.