so I got to thinking "HOW could this be anything to do with a tritone?

Then I was like "oh duh: Ab, is the b5 of D... so... is the bass doing a D at that point?

So then i look up bass for Smoke on the water

and dude is playing this

(no D whatsoever)
and it seems accurate to what I'm hearing on the original Deep Purple record

so yeah... still no idea what the deal is here