Five snare notes go by in the bar below and only two of them are meant to carry across a room. The backbeat tells you where; the ghost notes tell you how. A ghost note is a snare stroke played so quietly that it registers as texture rather than as an event, a whisper laid into the gaps between the loud snares on 2 and 4. They're not decoration; they're structural. Take the three of them out of this groove and you still have a beat, but you no longer have funk.
The bar stacks three simple layers. The hi-hat plays straight 16ths, all sixteen of them, unbroken. The kick stays out of the way with quarter notes on 1 and 3 and nothing else. The snare carries the rest: loud on 2 and 4, ghosted on the "&" of 2, the "e" of 3, and the "a" of 3. Beat 1 goes by with no snare at all, so the bar opens on hi-hat alone, and the last three snare notes crowd closer together as they run into the backbeat on 4.
Splitting the bar between your hands
The hi-hat never steps aside for the snare. At each of the five snare notes there's a hat note stacked on the same stem, so no one hand can cover both, and you can't pass the hat back and forth between your hands the way continuous 16ths are usually played. One hand rides all sixteen 16ths on its own and the other takes every snare note: right on the hat, left on the snare, for most players. At ♩ = 90 that's six hat strokes a second, so keep the motion small and let the stick rebound rather than lifting it for each one.
The left hand walks a fixed route: slap on 2, whisper on the "&" of 2, whisper on the "e" of 3, whisper on the "a" of 3, slap on 4. That last whisper and the slap on 4 are back to back, a single 16th apart, so treat the "a" as the run-up into the backbeat rather than a note of its own. The two volumes come from two stick heights. Ghosts start about 1 inch off the head and are played from the fingers; the backbeats start 10–12 inches up and are driven from the wrist, and the hand has to drop straight back down to ghost height afterward.
Building the 4-to-1 ratio
Add the layers in the order the difficulty arrives. Hands only first, no kick, slow enough that the three ghosts stay quiet under an even hat. Then set your stick heights on purpose and loop eight bars listening for one thing: the gap between backbeat and ghost, roughly 4 to 1 in volume. Bring in the kick on 1 and 3 last, since two quarter notes are the easiest layer in the bar and they won't disturb hands that have already settled. The backbeats on 2 and 4 carry accents on the staff and the ghosts deliberately do not, so you can see the shape as well as read it described. The Play button sounds it too: the two accented snares play at full volume and the three ghosts at a quarter of it, so you can hear the ratio you are chasing before you try to produce it. Hearing it is the easy half, and only your two stick heights will put it in the room.
Two failures arrive first. The ghost on the "&" of 2 rides the rebound off the backbeat in front of it and comes out nearly as loud, which flattens the bar into a busy 16th-note snare part. The ghost on the "a" of 3 drifts late and fuses with the backbeat on 4 into a flam. Record 30 seconds on a phone and play it back quietly: the two backbeats should still land, and the ghosts should read as motion underneath them rather than as five snare notes of equal weight. When you tire, the opposite failure shows up and the ghosts vanish altogether, which is the other way this groove dies.