If it has sound circuitry, it will also respond to MIDI commands from other keyboards or sequencers. A sound generating module is the sound circuitry alone, without any piano keyboard. These are usually in a small case, and they are an ideal way to add more sounds to your electronic orchestra. Yamaha, Korg, Roland, E-mu, Peavey, Kurzweil, Ensoniq and Kawai all make good keyboards and sound modules. Roland, Yamaha, Akai and E-mu make true samplers.
Drum machines are specialized sample playback units with a variety of drum sounds in memory.
They have memory for patterns of rhythms that can be chained together to make complete songs, and they can use MIDI timing signals to play in synchronization with the rest of your system or can be controlled directly from a computer sequencer through MIDI . Roland, Yamaha, Korg and Alesis make good drum machines. In most studio and performance music situations, an external sampler or sample playback unit would be preferable. Apple has licensed some of Roland's General MIDI sounds and included them with recent Macintoshes. This will give programs the ability to play back MIDI sequences and generate the sounds in software, rather than having to use an external sound generating module.