The SID chip is one of the most successful synthesizers of all time. Through rather small and fitting entirely on a single chip, the design of the chip was far ahead of it’s time. So far in fact that it’s one-of-a-kind sound is still in demand today. The SID chip, or MOS6581 has had songs named after it, spawned entire DIY communities, was the lead sound of a classic trance anthem, and gave birth to one of the most cutting edge hardware synthesizer companies today, Elektron whose first release was the SID station. With all these relatively recent accolades, it’s hard to imagine that this sound chip came out all the back in 1981. But regardless of era, this chip deserves to be remembered and acknowledged as the classic that it is.
The beginnings of the SID chip is tied to the hugely successful Commodore 64 computer in which it was the sound generator chip. It was in fact the first exclusive sound chip to be included inside a home computer. The chip was designed by a team of four headed by Bob Yannes. In an interview, Bob states that the design of the chip was inspired by the synthesizer industry. The resulting chip was designed in only five months. Interestingly, the original intentions were to actually sell it to synthesizer manufacturers alongside the personal computer industry. But the Commodore’s huge success completely dominated the supply and demand of the chip.
The technical design of the SID chip was impressive for it’s time. The original plan was to have 32 independent voices with their pitches controlled through a single high-precision oscillator. This turned out to be too ambitious for the time constraints and would have been mental for the time period had it become reality. The compromise for the overall synthesis architecture ended up being a single oscillator voice copied three times. Along with the three oscillator voices, an audio input was included, though it had no use at the time inside of a computer. Perhaps someone there knew that the extent of this chip may go far beyond the Commodore 64 in the future.
The 1980’s were a time of technological transition from the old analog world to the new digital one. Synthesizers of that decade were no exception and the SID chip in particular shows how this transition took shape. Though it might first seem that since it’s all in a microchip, it must be digital, this is not the case. The SID chip uses both digital and analog components inside. Digital was used primarily for the control functions while analog was used for the output. The result is a great sounding oscillator with a high level of accuracy and control. Though it may sound most similar to a DCO synth typical of the mid-80’s, the SID design is surprisingly most closely related to wavetable synthesis with it’s phase accumulating oscillator design.
Even though most listeners to the SID chip would be oblivious, the features of the SID chip were massive compared to many other synthesizers in the early 80’s. To start with, each of the three oscillators had four waveforms to choose from including saw, triangle, pulse, and noise. The oscillators themselves also had an impressive 8-octave pitch range. Sound shaping potential included a multimode filter capable of low, high, and bandpass modes. On the control side, the SID chip had 3 envelopes, 3 ring modulators, oscillator sync for each oscillator, and a random number modulation generator. Remember too that all of this and more was inside a rather small microchip.
One quirk of the SID chip is that there were two versions of it, each one with slightly different sonic characteristics. The first and most famous is the MOS 6581. This was the original specification designed in 1981. The second generation of the chip was named MOS 8580 and made several design changes to the original. The most significant of these changes was the operating voltage of each. The earlier 6581 ran on 12 volts while the later 8580 ran on 9 volts. Because of this difference, the 8580 overall runs cooler resulting in more stable components and less noise generated from the compoents. Additional changes with the 8580 included better mixing of the oscillator waveforms, better seperation of the analog and digital components, and a siginificantly different linear cutoff on the fitler versus an earlier logarithmic based one. Even with these changes though, the original 6581 is known to be the more desirable for it’s distortion, better bass, and overall richer sound.
Upon hearing the SID chip in action, it’s obvious that the sound it creates is unique with an attitude that cuts through the air nicely. In essence there is nothing else that sounds quite like it. Though it is “that sound” associated with early 80’s video games, the chip is capable of much more with it’s well thought out design. This opportunity was not missed by a certain Swedish company in the late 90’s. Though it builds some of the most cutting-edge hardware today, Elektron built it’s foundation on the SID chip with it’s first release, the SID station. This device basically took all the power of the vintage SID chip and wrapped a metal box with some knobs around it, giving easy control to all of the chips capabilities. The sound of the SID, through the SID station, even found it’s way into the memorable dance hit, Kernkraft 400 by Zombie Nation.
But the technology of the SID chip has lived on in far more numerous re-incarnations. The most notable is the rather large and devoted DIY community midibox.de. Though the community is primarily based around building custom DIY midi controllers, a large part of their projects revolve around ripping out a SID chip from a Commodore 64, and building a case with control knobs and LCD around it, similar to Elektron’s Sidstation. Below is an image of a MIDIbox SID synth in progress. The MOS 6581 chip is in the upper right, below the glowing LCD.
If building your own SID synthesizer from scratch sounds like too much work, there’s a bunch of other options available. First is the HardSID, a hardware box in which SID chips are loaded into and played back through a software interface. Continuing along the lines of modernizing a real hardware SID chip is the MSSIAH. It’s an actual commodore 64 cartridge that provides MIDI hardware and software control to access the SID chip inside. Finally, for those interested in a more virtual approach, the SIDizer software SID emulation synth is available from HyperSynth. Check out the links below for links to these sites and additional SID info.
SID chip site: http://sid.kubarth.com/