It's no secret that most anime is generously slathered with background music. Unless characters are talking, and sometimes even if they are, there's almost always BGM running in the background, a constant soundtrack for what's going on in the show. It's even a cliche than when the BGM cuts out, something serious is going on. Sometimes this BGM is used to communicate mood or comedy or the like, but often it is simply there.

SSSS.Gridman is an exception. From the start, one of the quietly unusual things about the show has been how little it uses background music. Rather than BGM, its passing moments and full scenes are filled with incidental environmental sounds; things like little noises of things thumping and squeaking, people's footsteps, the warning bells of railway crossings, the flapping and cawing of passing birds, doors opening and closing, rain falling, thumping machinery in the distance, the natural noise of busses humming along, and insects. Even when the show fills a silent time with background noise, it's not music; it's with, say, a quiet drone.

(There are times when music crops up in Gridman as diegetic sound, which is to say that it exists in the world and the characters hear it too.)

SSSS.Gridman does have background music, but it's rarely used. When the music starts up, things are about to happen, usually the kaiju fights or other climactic events touching on them. And generally the moment the fight is over, the music cuts out too. If there is music and it's not a fight, something important is happening and the show wants us to know.

(And Gridman generally considers fights over, at least for BGM, once the decisive blow has been struck. There is an explosion afterward, but the BGM does not continue through it in the way it might in another show.)

I'm sure that this is a deliberate decision on the part of the production. If nothing else, designing and putting together this soundscape has to be a lot more work than commissioning some BGM tracks and mixing them in underneath the vocals and any important foley sounds. But I don't know enough to guess why the show handled its sound this way. Perhaps it's for the same reason that the show had its animators draw a lot of what would normally have been background art, which is apparently to make the show's world feel more alive and real; see the Sakugablog discussion of this in their coverage of the first two episodes.

(Without knowing enough about anime production to be sure, I suspect that the prevalence of BGM in anime in general is because it is the simplest and cheapest way to fill in what would otherwise be completely dead silence (or voices talking in otherwise dead silence). Live action works can at least do scratch recordings during filming to have a basic 'bed' of background noise, but anime doesn't have that unless you deliberately go collect field recordings. Dead silence is somewhat unnatural in real life, which is probably partly why it's used for emphasis in anime.)

Looking back, one of the surprising things about this is how little I consciously noticed and notice both sides of BGM usage. For SSSS.Gridman, I didn't realize just how little BGM was used and how soon it cuts out. For other shows, I didn't realize how pervasive BGM usage was until I was spot-checking things as part of writing this and discovered, for instance, that it seems to be not unusual to continue BGM underneath even people talking, which is something I wouldn't have expected to need or use BGM. On the other hand, how pervasive BGM is seems to vary from show to show; I encountered others that had significant sections with only ambient noises and no BGM, although none that went anywhere as far as SSSS.Gridman.

(This is part of the 12 Days of Anime 2018.)