I've been re-listening to some tracks that I haven't heard in a while and I noticed some things that I'm trying to explain to myself. At rather obvious moments the drums will sound low then all of a sudden get loud. I know that this is done by merging two tracks together but how is that achieved in detail? I do some amateur recordings of my pieces and have attempted to fuse two tracks together to avoid the tedious process of re-recording but it doesn't sound like that. If I merge them, I can tell if the recording volumes get changed or I get closer to the microphone because the next track will overall sound louder/softer (I know how this can be fixed). But in the Beatles' case, all the other instruments sound at their normal levels at this juncture while the drums get louder. Anyone able to explain this?
In the song "I'm a Loser" during the guitar outro you can hear the ride cymbal all of a sudden cut out then cut in but the other instrument sound unaffected? I know there are tons of other tracks that you can hear track merging disparities but I wonder why it's the drums that you notice and no the instruments. Other examples include drums sound softer then all of the sudden louder.