I very much agree with
Dean on this point. And it is interesting how one can inter relate the musical arrangement and EQ in the engineering process.
The more things that are playing at once the harder in a way it is to mix. You also have to make compromises in terms of having to HPF things in order for all to get along. But if you limit say two as the total number of sounds that may be stepping on each or even three then you are going to have a much sparser mix and the parts need to play our much more in a serial manner than a parallel manner.
Very simple and very complex music can be realised and most often parts can interweave rather than all be on the same beats together. As a direct result of this the parts can be much fatter and the full amount of its sound can be let through.
This is why I enjoy loop recording midi and virtual/external instruments and switching tracks on the fly. You learn to start playing the parts much more serially and leaving even more space in between. First part of a bass line then followed by an electric piano lick, back to more bass line etc..
A lot of us are playing many parts to make our music and the trap is to overplay parts while doing this and building up the music. Before long it is already too busy and full. If so this is a good time to try and replicate everything you are hearing by cutting away lots of things that are overlapping and still leave the main essence behind. You are looking for the black backdrop behind all the music. Can you see it yet?
(Dark Side of the Moon has lots of black backdrop)
I find a lot of well written music for advertising interesting in that it sounds like there is more going on but with much less. The other day an ad came on with a killer drum sound bass and guitar. No chords yet it sound big and huge . Guitar playing catchy and fairly busy distorted lead melody. The parts were inter woven and you heard all three very clearly but nothing was stepping on each other though so the individual sounds smacked through big time much harder and clearer. All the EQ's were seriously fat on each part but as nothing was really stepping on each other it did not matter. It is a fatter result than trying to get 20 layers all working together in some ways applying HPF to most.
I agree with
Danny and
Bit about synths too. I have been recording them for years and most of them are too fat for their own good. They could never co exist untreated
(especially if the music is layered and many things playing at once!) But at least you are dealing with sounds that are usually too much and it is easier to take some of that away.
Kraftwerk is a great example of many parts and sounds that all exist and work together but none of them are stepping on each other much. So much space.
(That black backdrop is immense!) As a result the parts are EQed to sound great IMO. But the music can also be dense and heavily layered like
Brian Eno 'On Land Ambient 4'. Heaps of tracks all playing at once. But then it becomes EQ art once again.