Dub music is characterized as a "version" of an existing song, using B sides of 45 RPM records, called "version" which was usually the instrumental "version" of the song. Typically emphasizing the drums and bass for a sound popular in local Sound Systems. The instrumental tracks are typically drenched in sound processing effects such as echo, reverb, part vocal and extra percussion, with most of the lead instruments and vocals dropping in and out of the mix. Another hallmark of the dub sound is the massive low bass. The music sometimes features processed sound effects and other noises, such as birds singing, thunder and lightning, water flowing, and producers shouting instructions at the musicians. It can be further augmented by live DJs.