In pop music, vocalists commonly double their vocals to smooth out any imperfections that may occur. This is done by simply recording two or more takes and playing them together for a fuller sound. In hip hop music, however, doubling is often used to place accent on certain words or beat. For instance, sometime on the first or last word of a phrase may be doubled. A good example of hip hop vocal doubling can be found in the Beastie Boys song “Intergalactic.”
Two related vocal processing units are auto-tuners and vocoders. An auto-tuner takes the pitch of a vocal melody and adjusts it so that any note that is off-pitch is automatically tuned to the next nearest true pitch. You can hear the auto-tuner on songs by T Pain and Lil Wayne. A vocoder uses the shape of words made by a vocalist’s mouth, but takes its actual timbre from another instrument, such as a guitar or synthesizer. It was widely introduced into the mainstream by guitarist Peter Frampton, but has since been used extensively by artists such as the French electric artists Daft Punk. For a good example of its use by a hip hop artist, listen to “California Love” by 2Pac.
Some hip hop vocalists deliver many more lines of lyrics than vocalists in other genres. They also have to deliver them faster in order to meet the preferred 3:30 song length needed for commercial radio airplay. It is common for hip hop vocalists to lose their breath when recording vocals. So that there aren’t places in songs where you hear rappers gasping for air, they record their vocals many times. All of the takes are then spliced together for a smooth, consistent vocal delivery.
Hip hop music has featured percussion prominently since its inception. In addition to putting focus on beats, vocal delivery tends to be more percussive than pop music because hip hop vocals are closer to common speech than vocals that are sung. To accommodate this type of percussive delivery, vocalists use pop filters and compressors. A pop filter is a round, mesh screen device that goes between the vocalist and the microphone. It slows the air pressure of certain consonant sounds, such as B's and P's, so they don’t make a popping sound in the microphone. A compressor is an electronic device that, among other things, caps high frequencies and raises lower frequencies so as to create a smoother vocal delivery that is easier to mix over the music.