That was certainly the pinnacle of the Glover sound though it came about by accident/luck, not intent (Roger was always searching from album to album for a "better" sound). Hughes tried to emulate it on Burn, playing a Ric (which he had never done before), but even with the same engineer (Martin Birch) the sound wasn't the same. Though Hughes is a pick player like Roger, the bass on Burn lacked mids and wasn't really that audible (for Purple standards at least). It took Hughes until Stormbringer, when he reverted to a P Bass, to find his own studio sound (which he certainly has, live he was plenty individual from day one with ze Pürps) and stop the aping. His bass can be heard well on Stormbringer, though overall the production (courtesy of Musicland Studios, Munich) is a bit squeaky-clean (but has probably aged better than the Burn production sound, courtesy of the Rolling Stones Mobile Unit which had already served for Machine Head and Who Do We Think We Are).
But for some reason - and Gene Simmons is with me - I could always hear the bass better on DP albums than on Zep ones. I can't put a finger on why that is, these days - with decades of bass playing behind me - I can tune in on the JPJ sound no sweat. His bass wasn't mixed any less loud, he played with a pick too often enough and unlike Roger he didn't even have to battle with a raging Hammond in the frequency department, JPJ's bass lines were no less complex (sometimes even more so, Roger's bass playing is perhaps more accessible?), yet there are very few tracks where the bass line on a Zep song grabs you with immediacy.
