Yesterday I was working on a bass drum beat, and after adding some synths playing on top of it, I started to hear the bass drum echo. So, my first thought was I had accidentally enabled some kind of reverb or echo effect on it while I was setting up the synths. After confirming I hadn't and isolated the track to ensure the bass drum was sounding as intended, I chalked it up to some weird illusion between the synths and drum that was making it sound like an echo. I know it's not there in reality, but I can't unhear it.
In this case, I went back and added a little echo to the drum to make the effect intentional, which turned out to sound good, but sometimes I'll try to make the illusion reality and it doesn't have the same effect.
Would you be willing to export that track as two tracks--one with drums and one with synth? Then listen to them solo, then run them together (with WAV files instead of instrumentation)? Would be neat to have that illusion confirmed rather than it being a DAW artifact.
1. Play a pure saw wave sound for several seconds, it has to be loud (use headphones), then
2. hit the keyboard keys, or snap your fingers, or make other sounds with fast transients, and the transient is no longer snappy, it "whooshes". It's hard to describe but there is like a flanging effect on it.
I guess there is some scientific name for this phenomenon, but I don't know what.
A common thing to do is to pan a synth to one side, then add a very short (milliseconds) delay panned to the other side, which makes it sound like a very large sound played from a large distance away.
Another is stacking up a bunch of oscillators that are slightly detuned from each other, which again, makes the sound "big", because it sounds like many sources playing together, rather than one source.
Just using a "reverb" is generating an illusion of being in a large, echo-y space.
I do think that most producers don't really think of it as creating illusions, and more as making "cool" sounds.