Complex sentence: By the time they did record it for their fourth album, the rhythm had changed from a rockabilly shuffle to a gentle cha-cha with Ringo Starr keeping the beat by smacking his palms on his knees.
Split into simpler sentences: By the time they did record it for their fourth lp, the rhythm had changed from a rockabilly shuffle to a gentle cha-cha. And Ringo Starr kept the beat by smacking his palms on his knees.