A synth for creating drum sounds, which unlike the drum machine, is equipped with drum pads and intended primarily to be played by hand as opposed to sequenced. Drum synthesizers began appearing in the late 1970s with units from Syndrums and Synare; most of these were monophonic units with a single playing surface, limited patch editing capability, and no patch memory. The electronics were usually built into the playing surface enclosure, and since these units were intended to be played with sticks, the electronics were subject to the shock and vibration of playing, leading to reliability problems. The state of the art moved forward substantially when Simmons introduced their SDS-3 system in 1978. This was a four-voice system with four drum pads and the electronics mounted in a remote box.