It’s true that with a Mac Pro computer you can probably insert a D-Verb reverb plug-in on practically every audio track in your Pro Tools session. However, this is a clear cut case of, “Just because you can do it doesn’t mean you should.” Reverb should be applied as a parallel effect, on a bus, in the send/aux return position. There are a few reason’s why:
1) The purpose behind reverb is to mimic the ambiance that’s captured during the recording of a live performance. With multitrack recording, performances are recorded at different times, often in different spaces, and sometimes with no ambience at all (as in the case of a direct line input recording or a virtual instrument). Consequently, there is an absence of the cohesive ambiance that naturally occurs in a live recording situation. Placing a reverb on your mixer’s bus let’s you send an appropriate amount of signal from each performance in your session through the same virtual space, just as if you had recorded everything live, in one space.
2) Reverb creates a sense of depth in your mix, of front to back space. The more reverb a signal is blended with, the further back in the mix it will sound. Alternately, the less reverb a signal is blended with the closer it will sound to the listener. By using a channel’s send to add different amounts of reverb to a performance you can bring an instrument forward, or push it to the back of your virtual sound stage. For example, a lead vocalist can be made to sound in front of the stage by mixing her with only a little reverb, while a cello can be made to sound at the far back of the stage by mixing it with much more reverb.
Always keep your reverb’s dry/wet mix parameter set to a 100% processed return. The reverb effect is created by mixing the dry channel signal with the wet reverb effect return. If your reverb’s dry/wet mix parameter is less than 100% you’re just returning dry signal back into your mix, and this is not the object. Use a channel’s send to adjust the amount of reverb you want mixed with a track. The higher the send level the more reverb effect return you’ll hear for that track.
3) Reverb, used correctly, on a mixer’s bus (in parallel), sounds superior in both clarity and depth than individual reverb plug-ins inserted on each mixer channel. When it comes down to it, that’s really what matters, it just sounds better.
In most modern DAW mixers you can send to a reverb in either mono or stereo. I prefer a mono send and a stereo return for most projects (such as dance, hip-hop, and alternative). However, a stereo send and a stereo return is equally acceptable and I often use this configuration when I want to achieve a higher degree of separation and fidelity (for example, a sparse acoustic recording or string quartet). Pictured below is a mono send/stereo return reverb configuration for Pro Tools (notice my choice of the “mono/stereo” version of the D-Verb reverb plug-in). I’m also attaching a Zip of a Pro Tools 7.3 session so you can dig around and see first-hand how it’s all set up.