In the early days of rap, producers got their drum tracks by sampling vinyl records. The imperfections of the vinyl gave the drums a gritty, warm sound that played well against the mid-range frequencies of the vocal track. Two simple methods can reproduce that gritty sound without vinyl sampling. Modern samplers, both software and hardware, sample at CD-quality 44.1 kHz by default. Reduce the sample rate to 22 kHz to approximate a vinyl sound. A software bit crusher can also add a vinyl-like warmth by reducing the resolution of a drum track.
The simplistic nature of most rap drum patterns adds extra emphasis to each drum hit. Layered samples produce thicker, heavier beats with minimal effort. When played simultaneously, two kick drum samples with slightly different qualities merge into a single thick sound. Layering a snare sample and a clap sample produces a sound with more punch than the individual sounds could provide. Adding a low-pitched sine wave under a kick sample creates a window-rattling sub-bass
Rap beats need tightening to keep individual drum hits from bleeding into each other and to provide maximum emphasis for each hit. For example, a kick that overlaps the bass notes creates a muddy sound that ruins a track. In the case of individual drum hit samples, adjust the attack and decay to prevent bleeding. For full-length drum loop samples, a beat slicer helps. Beat slicers chop up longer samples into individual components. This allows the producer to sample individual drum hits from the loop and adjust them as needed.
If all else fails, use commercially available drum loop sample CDs. Numerous companies sell sample compilations made specifically for rap producers. The companies produce the samples in professional studios. The CDs contain samples in multiple audio formats for compatibility with multiple software packages. Professional loop compilations also avoid the tricky copyright issues that surround vinyl sampling, an issue that plagues many rap producers.