Boom Bap

What it is

New York from about 1988 to 1996, and the default setting for sample-based rap ever since. The name is onomatopoeia for the kick and the snare, and the sound is what happens when you put a funk break through an SP-1200 or an MPC60 and let the machine's limits do the arranging. Twelve-bit converters running at 26kHz, a filter that could not help colouring things, and eight seconds of sampling time that forced producers to chop rather than loop. Boom bap is East Coast hip-hop's centre of gravity: the golden era, the underground that followed it, and most of what people mean when they say a beat sounds like real hip-hop.

What it sounds like

Dirty and mid-forward. A kick with a woody thump rather than a sub, a snare that cracks and then leaves a short tail of room, and hi-hats running sixteenths at four different volumes. Underneath there is a chopped loop that has been filtered, resampled and pushed until it distorts a little. The whole thing lopes because the offbeat sixteenths are late, and it breathes because a third of the snare hits are barely audible. Bass is usually the sample's own bass, filtered low and doubled with a sine.

Key elements

• Ghost notesSnare hits at velocity 25 to 55 sitting between the backbeats. They are not decoration. Remove them and the pattern stops being boom bap and becomes a rock beat played slowly.
• MPC swingThe offbeat sixteenths pushed late, typically between 54 and 58 percent. The MPC60 defaulted to 54 and a very large share of the canon simply never changed it.
• The chopped loopFour bars of a jazz or soul record cut into pieces and replayed out of order, so the sample carries the harmony but no longer carries its original groove.
• Twelve-bit gritThe SP-1200 sampled at 26kHz with 12 bits and the resulting aliasing and quantisation noise became the sound rather than a fault. Modern plugins model it because people want it back.
• A filtered basslineA low-passed sample of a bass note, or a sine tuned to the sample's root, playing something simple that stays out of the kick's way.

How to get them

• KickLayer two: a short acoustic kick for the attack around 900Hz and a sine or an 808 tail tuned to the root for the weight. Keep the whole thing under 400 milliseconds so it stays a thump.
• SnareOne sharp snare for the crack and a second, longer sample sent to a short plate around 0.9 seconds. Compress the pair hard with a 30ms attack so the transient survives.
• GhostsTake your main snare, drop the velocity to 30, high-pass it at 500Hz and place hits on the sixteenths either side of the backbeat. Vary each one by five or ten so no two match.
• The sampleChop on transients, not on the grid, then quantise the chops with 50 percent strength so they keep some drift. High-pass the loop above 200Hz before it meets the kick, or the two will fight for the same 80Hz.
• DirtResample the finished drum bus at 12 bits and 26kHz, or run it through a bitcrusher set there. Then low-pass around 12kHz. That is the SP-1200 in two moves.
• SwingSet 56 percent and leave it. If the beat sounds stiff, the problem is almost always flat velocities rather than the swing amount.

Reference points

DJ Premier, Pete Rock, Large Professor, Marley Marl, RZA, Buckwild, Diamond D, and later Apollo Brown and Nicholas Craven. Named as reference points for the sound, not as endorsements or as anyone to imitate.