Eventually, the bass line drops down an octave and changes its stubborn pedaling to play chord tones along with the rest of the rhythm section. It starts with the same old D and A. Next, it moves to C♯ and A for the A chord. Then it moves to the B chord but still keeps the pressure on with that non-chord-tone A. Finally, it rounds off with a pleasant, resolute walk-up, bouncing back up between notes of the major scale and A, which is the root of the chord. Classic!
Getting a space prepped for a recording session takes a considerable amount of time. If you’re recording clients, or guest musicians, or just helping out a friend, always try to ask for a specific tech plot in advance so you can plan accordingly. There’s nothing that will suck the inspiration and energy right out of the room more than waiting around to set up mics and inputs when the musicians are already done setting up their gear.