That, presumably, is the old parallel twin Bonnie.
The AJS and BSA (Goldie preferred) sounded good too, and just for sound the old sloper Panther was gorgeous (useless as a solo bike, good to pull a chair) but surely the king of the bike sounds was the Thruxton Venom, with the sharp bark of the exhaust melding with the insistent whine of the gearbox. Or maybe a Manx Norton.