Empirically, mainly watching Stephen Malinovwski's (smalin) music visualization videos on YouTube, I have noticed that several instruments playing together sound better when they roughly cover the spectrum evenly. (This is probably not the right language).
I mean the following. Suppose I have two instruments playing in perfect harmony, the same note several octaves apart, say C1 and C5. I have seen that if the space in between is also played by other instruments, say playing C2 and C3 or other notes in between the sound is more pleasant, to me. So, if there are no big gaps the music sounds like it has more body, or depth, or seems more robust. It is hard to describe the perception of it as it might be personal.
I am, for the moment at least, focused in writing music that sounds that way. Since I don't read the score very fluently I often use Malinowski's software to check that what I wrote doesn't have those big gaps between instruments as a way to get the quality of the sound I am seeking.
My question is: Can this property of having 'full body', 'depth', or 'being robust' be obtained even having big gaps between instruments?
Clearly the property I want is very subjective, but perhaps you have your own idea of what it is and it coincides with what I mean. I would like mainly to see examples in which big gaps between instruments exists but still the orchestra sounds with this 'full body' sound in your opinion. Then I can decide if it also sounds to me like that.
I am trying to learn what properties of the composition contribute to this quality of the sound I am looking for to then apply is consistently and not obtain it just by accident.
Important: Take as the meaning of 'robust' your own interpretation of it. Otherwise if you take as definition (The sound you get when the instruments cover evenly the spectrum) the question is not interesting because it becomes the negation of a tautology.
Edit: An analogy that came to my mind to try to explain the quality of the sound I am trying to describe. When drawing with pencil, for example, sometimes the drawing looks smudged if there are lots of area with a similar shade of gray. I don't want that in the sound. It is like getting the right white balance and not too much and not too little contrast in a photography. What to aim when composing for an orchestra to try to get the analogous property in the sound?