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Sunday, August 7th, 2022 08:48 am

Synth Glossary

Additive Synthesis:
A system for generating waveforms or sounds by combining basic waveforms or sampled sounds prior to further processing with filters and envelope shapers. ...


"Oberheim's first instrument was a monophonic synthesizer module, the Synthesizer Expander Module, or SEM as it became known, originally built to be used in conjunction with someone else's instrument (e.g., an ARP or a Moog). Although polyphony at this time was accepted as the domain of pianos, organs and string machines, every manufacturer was desperate to crack the problem of polyphonizing the synthesizer. "Oberheim's answer was astoundingly simple: box up a bunch of SEMs. And this is exactly how the 4-Voice and its big brother, the 8-Voice, were put together. "An elegant solution in some respects, but hooking up four or eight self-contained instrument modules and linking them to a digitally scanned keyboard also threw up some major problems, the foremost of which is tuning. In order for a chord to sound remotely acceptable, for example, the tuning of all of the SEMs had to be sympathetic, which is no easy matter when dealing with drift-inclined analog oscillators and relatively coarse control knobs. The result was, and remains, that these instruments are not for the fainthearted or inexperienced. They require constant attention, patience and no small amount of skill. "The reason people bothered then and continue to bother about them now is that, handled correctly, the Oberheim 4-Voice and 8-Voice instruments have a depth and majesty about them that is unique. Those familiar with Weather Report's "Birdland," on which Joe Zawinul employed one of the first of these instruments to roll out of Los Angeles, will no doubt agree.

"The 4-Voice is simply four cream-faced monophonic synth modules lashed together in a wooden case covered with black vinyl and wired up. Controls on these self-contained modules comprise two VCOs; a two-pole filter that can operate in highpass, lowpass or bandpass modes; a simple LFO and a pair of ADS envelope generators. If you play a single note on the keyboard, an LED indicates which of the modules you are triggering, allowing you to then twist and tweak its sound into the one you want. In order to have this sound triggered polyphonically, you must recreate your programming setup on each of the other SEMs. A year after the initial release, Oberheim launched a programmer which lets you store 16 setups in memory. (This helps, of course, but the programmer is not a foolproof device.)

"Each or an SEM's pair of oscillators offers a choice of sawtooth or variable-pulse waveforms, the pulse width variable from 10 percent narrow to 90 percent narrow via a 50 percent "square" shape. Pulse width can be used as a modulation destination in a rotary-controlled contest with oscillator frequency (i.e., pitch). Mod sources include the LFO, which is preset to a smooth, vibrato-inducing triangle wave; the second envelope generator; or an external controller. The envelope generators themselves offer only attack, decay and sustain parameters, with decay effectively doubling up as release. The filter can be switched between its various modes, and there are rotary controls for cutoff frequency and resonance. Again, the filter can be modulated positively or negatively by the LFO, envelope 1, or an external source.

"The controls are all large and clearly labeled. Fundamental comprehension is not the problem on one of these instruments.

"Although the overall length is 1066mm, the actual keyboard is only four octaves long. A good deal of space is occupied by the 16-channel programIner (originally an optional extra), which houses not only program select buttons but a simplified version of an SEM. The trick is to set up the programmer's controls to conform to those you have been fiddling with on the main panel. Unfortunately not all the parameters are offered, so you can't always store the exact sound as you'd like. There are no resonance control, bandpass, lowpass or highpass options for instance."

"There are various ways in which the SEMs can harnessed. Most commonly, you assign the instrument to move sequentially through each SEM in turn. Alternately, you can remain frozen on one for the first note played, then step through the others. You can also split the keyboard. Controls for these various modes of triggering, along with portamento, pitch control and VCF cutoff point maneuvering, lie immediately to the keyboard's left, beside the programmer.

"Since you have four separate instruments to work with here, it's hardly surprising that there are four separate outputs; each can be mixed in level and altered in pan position. The "spread" that you can produce is substantially responsible for the instrument's spacious, "big" sound."

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