Oberheim DMX
A drum machine produced by Oberheim starting in 1980. Introduced hot on the heels of the Linn LM-1, the DMX was the second drum machine on the market to employ recorded digital samples of real drums, rather than trying to imitate drum sounds with analog circuitry. It was also Oberheim's first drum machine design.
The voice architecture consisted of eight voices, each of which could play any one of three drum samples at a given time. On the panel, each voice was arranged with three buttons allowing any of the voice's three samples to be played, and a fader which determined the level of that voice in the mix output. Two of the voices were allocated to toms, one to snare, one to kick (bass), one to hi-hat, one to cymbals, and two to miscellaneous percussion. The snare, bass and the two tom channels actually each had only one sample, with three different choices of emphasis (volume). The hi-hat had a closed and an open sample; the cymbals and percussion voices each had three different samples. Each voice had an individual output on the back panel, in addition to feeding the mix output. A ninth output provided a click track, driven by the internal metronome.
The built-in seqeuncer worked at two layers, called the "sequence" layer and the "song" layer. At the "sequence" layer, the performer could create a number of short patterns, each of which constituted a sequence. Both real-time (with quantization) and step editing methods of recording sequences were available, and existing hits in a sequence could be copied or deleted. Allowable tempo range was from 25 to 250 beats per minute, and a number of time signature values were supported. Although a seqeunce could be up to 99 bars, it was expected that most sequences would be 2, 4 or 8 bars. At the song layer, a "song" was basically a list of sequences to be played. Each sequence in the song could be repeated any desired number of times, and each sequence could play at its own tempo and time signature. Memory was specified as being 2000 "events", where an "event" is a point at which one or more drum hits occurs simultaneously. However, it is implied in the manual that some memory is consumed by other sequence and song data.
The DMX was capable of synchronizing with a Oberheim DSX digital sequencer via CLOCK IN and CLOCK OUT jacks. The DMX could be either the master or the slave; in slave mode, it would start together with the DSX and follow the DSX's tempo. A output for writing a sync signal to a track on a multitrack tape was also available. (The user manual, unfortunately, does not specify what the formats of these signals are.) At some point, the "Oberheim System" parallel control interface was added, which made it possible to play the DMX from other Oberheim gear that had this interface. Also on the back panel were a pair of Molex connectors; one allowed individual channels to be played by external trigger signals, and the other allowed playback speed of samples to be changed by an external control voltage. The user who wished to exploit these had to obtain the proper matching Molex connectors and fabricate their own cables.
The samples were stored on EPROMs. Oberheim offered a device called the Prommer that could record samples, apply the proper compression (mu-law), and then burn the result to an EPROM, which could replace a factory EPROM. The user still needed to have some knowledge of how drum samples were stored in the EPROMs, but the Prommer automated much of the process. Sequence and song memory was somewhat problematic: The DMX contained a rechargeable NiCad memory backup battery which was changed whenever the DMX was plugged in and powered on. This battery ran down after a week or two of non-use, so the smart user employed the cassette interface to save their sequences and songs. Today, nearly all of the original batteries have failed (and some leaked inside the case), leaving the units with no memory backup. Factory example sequences and songs came in a cassette tape packaged with the unit, which the user could load.
In 1983, Oberheim offered the DX, a cut-down version of the DMX with only 6 voices, and some other features were omitted. Still, it was offered at half the price of the DMX, and became a hit with much of the hip-hop and dance crowd.