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A polyphonic analog synthesizer produced by Oberheim in the mid-1980s. It was designed to solve the problem that most polyphonic synths of the era had: limited signal routing capability. Instead of switches that provided a few options for routing of modulation signals, which was the usual practice of the time, the Matrix-12 used the matrix routing concept. This allowed any of a long list of sources to be routed to a number of possible destinations. It was implemented within hardware and software inside the synth, and required no patch cords. The matrix implementation solved the problems of signal loading and matching internally, and allowed the level of signal routed to a particular destination to be controlled.

Conceptually, the routing matrix consisted of a grid of inputs and outputs similar in fashion to a pin matrix,with signal sources on one axis and destinations on the other. The matrix was equipped with 12 "crosspoints", analogous to the pins in a pin matrix, each of which could be set on a grid intersection to connect a source with a destination. The crosspoints had the ability to be set to attenuate and/or invert the signal. Unlike a physical pin matrix, this electronic matrix took care of electrical concerns such as routing multiple outputs to one input without loading down the outputs, or causing crosstalk.

In addition to the matrix routing, the Matrix-12 provided a large variety of modulation sources, and some other unique features. Each voice had access to five LFOs and five envelope generators which were connected to the matrix, in addition to some standard routing which was always active. The EGs produced five-segment envelopes with an initial delay option, and could be made to retrigger off of an LFO so that a voice, once triggered, would sound continuously. A unique device called a "tracking generator" could convert any varying input signal into a piecewise-linear continuous function, and the result was available on the matrix. External controllers and MIDI Continuous controllers could also be routed through the matrix.

Another unique feature of the synth was its filters. Implemented using a very versatile integrated circuit from Curtis Electromusic, the filter offered a variety of complex response curves in addition to the usual low pass, bandpass, and high pass responses. They also offered varying stages of filtering ranging from 1 to 4 poles.

The Matrix-12 tried to solve the problem of the user interface for a very complex synth by using a "paged" display concept. The panel contained several displays, each capable of displaying a single line of text. A display offered a variety of pages, each containing a few parameters that could be adjusted; a second display vertically in line with the first showed the current parameter values. Soft knobs in line with the second display adjusted the displayed values. Additionally, the panel contained a silkscreened legend of the available pages and what order they would appear in as the page buttons were pressed. However, many users still found it frustrating due to the sheer number of parameters and pages. (John Bowen Synth Design greatly expanded and improved on the paged display concept with the Solaris).

Oberheim also produced a variant called the Xpander (not to be confused with its earlier Synthesizer Expander Module, and in the process, it inadvertently invented the tabletop synth packaging. The Xpander was a 6-voice version of the Matrix-12, with a few less features, but some unique features of its own. It offered both MIDI and CV/Gate control over each voice, and could convert CV/gate inputs to MIDI outputs. It also provided individual outputs for each voice, and in a certain MIDI mode it could be used effectively as 6 monophonic synths in one box. The most unusual aspect was the packaging: it was in the same case as the Matrix-12 but without a keyboard, intended to be controlled externally, which made it one of the first tabletop synths. (Although it was far larger than more recent tabletop synths.)

The Matrix-12 was a high-end synth when it was introduced, and it remains so today. It and the Xpander are highly desired by collectors, and valuations are quite high. Reliability is generally considered good, although the displays are of a type called "vacuum flourescent" that requires high voltages and can be physically broken if the synth is handled roughly. Some units have had power supply issues, and some of the Curtis ICs are uncommon designs that are impossible to replace if they fail.

In the late '80s Oberheim produced another synth called the Matrix-6. This was similar in concept, but used a very different voice architecture.

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