A musical instrument that generates sound electronically and is designed according to certain principles developed by Robert Moog and others in the 1960s. A synthesizer is distinguished from an electronic piano or electronic organ by the fact that its sounds can be programmed by the user, and from a sampler by the fact that the sampler allows the user to make digital recordings of external sound sources. Synthesizers, particularly if provided with MIDI software and hardware, need not have a keyboard, and most need to be connected to amplification equipment if they are to be heard. See also master keyboard, tone module.