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Oberheim | SEM

Description

The SEM was Oberheim's first official analog synthesizer. SEM stands for Synthesizer Expander Module. It was conceived with the notion of being used as a backup synth connected to a sequencer for layering or beefing up your existing monophonic analog synths. The SEM itself was a keyboard-less module with two analog oscillators, a 2-pole multimode filter, ADR envelopes, and an LFO. Each of the two oscillators offer triangle or rectangular waveforms. But unlike the Moog and ARP counterparts of the time, the SEM's 2-pole (12dB/oct) filter was a little thin. The others used a 4-pole (24dB/oct) filter which has a steeper roll-off and so it sounds much better. But the SEM's filter offered many modes in addition to low-pass, including high-pass, band-pass and band-reject.

Although SEM modules and other external controllers could be inter-connected, the SEM is not a patchable synth module like other modular type synths of the time. Its signal routing was more or less, hard-wired. The SEM was for all purposes, an accessory. But Oberheim jumped into the synth market by coupling SEMs with a keyboard and an analog sequencer into a compact, white, little performance synth. That led to the Two Voice, Four Voice and Eight Voice models. And from there, came the rest of Oberheim's history of instruments. Some earlier SEMs have several differences in their circuit design that affects the envelopes, filter, etc. If your SEM has "1080" written inside, it's an early one. If you see "1180", it's the "normal" one that most people know and love.

BrandOberheim
ModelSEM
DeviceSynth
TypeDesktop
Engine TypeAnalog
EngineVCO
Voices (max)1
Oscillators2
LFO1 Triangle
Engine Detailed2 VCO's (per voice) with sawtooth or variable-pulse waveforms
Filter (VCF)2-pole multimode (low-, band-, hi-pass, band-reject) VCF with ASR (Attack, Decay and Sustain) generator
Envelope (VCA)2 ADR (Attack, Decay and Sustain) Envelope Generators
SequencerMini Sequencer (with 8 steps and 2 voices)
Keys0
Key typeN/A
VelocityN/A
AftertouchN/A
CV-gateCV/Gate
Produced:1974 - 1979
Legend: Obvious Y: Yes, N: No, N/A: Not Applicable
VCO Voltage Controlled Oscillator DCO Digital Controlled Oscillator
LFO Low Frequency Oscillator Sub Sub Oscillator
VCF Voltage Controlled Filter VCA Voltage Controlled Amplifier
Velocity As with a piano, the harder you hit a key, the louder the sound, unlike most organs which always produce the same loudness no matter how hard you hit a key. Aftertouch Pressing a key after you activated it. Channel Aftertouch, no matter which key, it will send a Channel message. Poly Aftertouch, sends the pressure per key instead of the whole channel.
Values for OSC, LFO, Filter, Envelope are per voice unless stated otherwise.

Manuals, patches etc.

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