The Purdie shuffle is one of the most over-quoted and under-played grooves in popular music. Bernard Purdie put it on countless Steely Dan and Aretha Franklin records and it has been imitated, half-imitated, and badly imitated for fifty years. The actual groove is harder than it looks — what makes it sound like a Purdie shuffle is not the basic skeleton (which is just a half-time shuffle) but the ghost notes on every triplet partial that fill the space between the loud snare hits.
If you can hear every single triplet of the bar — twelve triplets in a 4/4 bar, played as 8th-note triplets — then you have it. If any of them disappear, you don't.
Half-time shuffle: the loud backbeat lands on count 3 only (not 2 and 4). The hi-hat plays a swung pattern — typically the first and third triplet of every beat, leaving the middle triplet open. That's the basic shuffle on its own.
Now: every triplet partial that does not have a hi-hat or a loud snare on it gets a ghost-note snare. Every single one. The result is a groove where you hear hi-hat, ghost, hi-hat across the first beat — twelve audible articulations per bar. The loud snare on 3 cuts through that carpet like a slap. Played correctly, it sounds inevitable.
Kick figures vary, but the canonical placement is on count 1 and on the third triplet of count 2 (the "a" of 2 in shuffle-talk). That single anticipation pulls the snare on count 3 out of you — you hear the kick land just before, and the loud snare answers it.
The Purdie shuffle wants to live around ♩=80. Slower and the ghost notes lose definition; faster and they collapse into a buzz. Practise at 80, then drop to 70 to dig deeper, then push to 90 to test the time.