The original Synthesiser Expander Module (SEM) was released by Tom Oberheim in 1974 and designed to be used in conjunction with the Oberheim DS-2 sequencer.
Back in the days of monophonic synthesisers, the idea was that the SEM and DS-2 would provide an additional sonic palette complementing the existing Moog or ARP synthesisers for sale at that time. Essentially, a SEM/DS-2 combination would play a sequenced pattern while the musician played over the top on their Moog or ARP.
Oberheim DS-2
To this end Tom’s objective was to design the SEM with a basic but essential set of controls, with the express aim of it being a great sounding synth that was simple to operate.
At that time the most common filter was the 24dB per octave lowpass found on the Minimoog and ARP Odyssey. But after being particularly impressed by Dennis Colin’s 1047 Multimode Resonator Filter module used on the ARP 2500, Tom commissioned Dennis to design a 12dB filter which provided Lowpass, Bandpass and continuous Highpass options. This wonderful sounding filter became the core of the SEM and helped set it apart from anything else out there. Combined with two stable VCOs which were designed by E-mu’s Dave Rossum, it’s no exaggeration to say a legendary synth module was born.
The SEM, which provided the foundation for Tom’s 50 year plus career in synthesis, would eventually be revived in 2009 due to popular demand.
Oberheim SEM
*“The SEM was developed for two main purposes: As a simple but capable synth voice to complement the DS-2, and as a device that could complement the sound of the ARP 2600 and Minimoog. So I decided to use a 2-pole, multimode filter in the SEM to add more sound capabilities when matched up with the 4-pole 2600 and Minimoog filter.”
Interestingly though, Tom considered the SEM to be a ‘panic product’ after the effects units he’d made for the Chicago Musical Instrument Company (later Norlin) cancelled all their orders after they acquired Moog Music. So in a roundabout way, Bob Moog was indirectly responsible for the inception of the SEM, which was rapidly designed and created by Tom in order to keep his business afloat and his employees paid.
The SEM was a huge success and because it sounded so good, it quickly became the backbone for the Two-Voice, Four Voice and Eight-Voice instruments that followed. However, a single SEM remains a thing of physical and sonic beauty - still highly sought after by electronic musicians nearly 50 years later.
Oberheim TVS (Two-Voice)
*“When Norlin cancelled all their pedal orders in January 1975 I had to decide what to do to keep my company going. So I quickly decided to use the SEM module which already existed, combined with a polyphonic scanning keyboard that I licensed from E-Mu Systems (which Jim Cooper and I modified to add some additional keyboard modes) put it in a Tolex case and then showed it at the 1976 NAMM show in Chicago in June of 1976.”
Having released the Eight-Voice GForce Software OB-E, you may wonder why we also developed the GForce Software SEM? Well, the answer is simple…in more ways than one.
The eight voice is a complex instrument to which only the adventurous might gravitate. On the other hand, the simplicity of a SEM makes it perfect for both beginners and seasoned professionals. It sounds sublime and yet provides the perfect introduction for those just getting started, or to those whom synthesis isn’t a life-statement and just want something quick and easy when it comes to finding an inspirational sound.
We think the SEM is perfect for those more interested in focusing on their composition and not the finer intricacies of synthesis. And unlike many synths out there, we’ve witnessed first-hand that it’s harder to make a SEM sound bad, than it is to make it quickly sound great.
Obviously, we’ve thrown in a wealth of patches to get you started, plus a few additional bells and whistles including: