From Academic Kids
Most modern drum machines are sequencers with a synthesizer, sampler, and/or a sample playback (rompler) component that is tailored to reproduce the sounds of drums and other traditional percussion instruments. Though features vary from model to model, many modern drum machines can also produce unique sounds (though usually percussive in nature), and allow the user to compose unique drum beats.
Early Drum Machines
Early drum machines were often referred to as "rhythm machines" and played only preprogrammed rhythms such a mambo, tango or the like. The first rhythm machines were included in organs, in the late 1960s, and were intended to accompany the organist.
The Rhythm Ace was the first stand-alone drum machine. It was released around 1970 by a company then called Ace Tone (later called Roland). The Rhythm Ace was a preset-only unit; it was not possible for the user to alter or modify the pre-programmed rhythms. A number of other preset drum machines were later released in the 1970s.
Programmable Drum Machines
In 1979, The Roland CR-78 drum machine was released. It was one of the first programmable rhythm machines, which allowed the user to create their own beats. Later that same year, Roland offered the Boss DR-55. It was the first fully programmable drum machine for under $200. The DR-55 had all of four sounds, and memory enough for only 16 rhythms: hardly passable by modern standards, but in its time, the DR-55 was a relatively affordable breakthrough.
The Linn LM-1 (released in 1980 and pricey at $5000) was the first drum machine to use digital samples. Its distinct sound can be heard on many records from the early 1980s, such as The Human League's Dare and Men Without Hats' Rhythm of Youth. The famous Roland TR-808 came out months later; while the TR-808 did not have digitally sampled sounds, it was far less expensive.
Drum machines using digital samples were a good deal more popular than the TR-808 in the early 1980s. The TR-808's sound only became truly desirable in the late 1980s, about five years after the model was discontinued. The TR-808's and the TR-909's beats have since been widely featured in pop music, heard on countless recordings.
Because these early drum machines came out before the introduction of MIDI in 1983, they used a variety of methods of having their rhythms synchronized to other electronic devices. Some used a method of synchronization called DIN-synch, or synch-24. Some of these machines also output analog CV/Gate voltages that could be used to synchronize or control analog synthesizers and other music equipment.
Drum machines can either be programmed in real time (the user hears a metronome and plays beats in time with the metronome) or in step time, where the user specifies the precise moment in time on which a note will sound. By stringing differently-programmed bars together, fills, breaks, rhythmic changes, and longer phrases can be created. Drum machine controls typically include Tempo, Start and Stop, volume control of individual sounds, keys to trigger individual drum sounds, and storage locations for a number of different rhythms. Most drum machines can also be controlled via MIDI.
By the year 2000, stand-alone drum machines became much less common, being partly supplanted by general-purpose hardware samplers controlled by sequencers (built-in or external), software-based sequencing and sampling, and music workstations with integrated sequencing and drum sounds. TR-808 and other digitized drum machine sounds can be found on archives on the Internet. However, traditional drum machines are still being made by companies such as Roland Corporation (under the name Boss), Zoom, Korg and Alesis, whose SR16 drum machine has remained popular since the early 1990s.
There are percussion-specific sound modules that can be triggered by pickups, trigger pads, or through MIDI. These are called drum modules; the Alesis D-4 is a popular example. Unless such a sound module also features a sequencer, it is, strictly speaking, not a drum machine.