Hip-hop music is a musical genre which developed alongside hip hop culture, and is commonly based on concepts of looping, rapping, freestyling, DJing, scratching, sampling and beatboxing. The music is used to express concerns of political, social, and personal issues. Hip hop began in the Bronx in New York City in the 1970s. Beats, almost always in 4/4 time signature, can be created by looping portions of other songs, usually by a DJ, or sampled from portions of other songs by a producer. Modern beats incorporate synthesizers, drum machines, and live bands. Rappers may write, memorize, or improvise their lyrics and perform their works a cappella or to a beat.