MOS Technology 6581
Together with the VIC-II graphics chip, the SID was instrumental in making the C64 the best-selling home computer in history,[2] and is partly credited for initiating the demoscene.
The SID was devised by engineer Bob Yannes, who later co-founded the Ensoniq digital synthesizer and sampler company.
Yannes headed a team that included himself, two technicians and a CAD operator, who designed and completed the chip in five months in the latter half of 1981.
Yannes was inspired by previous work in the synthesizer industry and was not impressed by the current state of computer sound chips.
[3][4]: 235 I thought the sound chips on the market, including those in the Atari computers, were primitive and obviously had been designed by people who knew nothing about music.
[4]: 236 The support for an audio input pin was a feature Yannes added without asking, which in theory would have allowed the chip to be used as a simple effect processor.
Each voice may be routed into a common, digitally controlled analog 12 dB/octave multimode filter, which is constructed with aid of external capacitors to the chip.
Due to imperfect manufacturing technologies of the time and poor separation between the analog and digital parts of the chip, the 6581's output (before the amplifier stage) was always slightly biased from the zero level.
By quickly adjusting the amplifier's gain through the main 4-bit volume register, this bias could be modulated as PCM, resulting in a "virtual" fourth channel allowing 4-bit digital sample playback.
The first instance of samples being used in actual musical compositions was by Martin Galway in Arkanoid (1987, Imagine), although he had copied the idea from an earlier drum synthesizer package called Digidrums.
The software trick generally renders one voice temporarily unusable, although clever musical compositions can make this problem less noticeable.
An excellent example of this quality improvement noticeably reducing a sampled channel can be found in the introduction to Electronic Arts' game Skate or Die (1987).
Luckily, the situation can be remedied by using the waveform control test bit, which in that condition injects one 1-bit into the XOR shift register.
The 6581 is very sensitive to static discharge and if they weren't handled properly the filters would stop working, explaining the large number of dead 6581s in the market.
Evil Laboratories used it in their SID Symphony expansion cartridge (sold to Creative Micro Designs in 1991), and it was used in a few other places as well, including one PC sound-card.
Also, the highpass component of the filter was mixed in 3 dB attenuated compared to the other outputs, making the sound more bassy.
Over the years, the design of this filter differed with each subsequent chip revision, lending each its unique sonic fingerprint.
[12] Moving to the latter models, the updated 8580 SID chipped marked its introduction in newer versions of the Commodore 64 machines.
Technically compatible with the 6581 software, the 8580 brought with it a unique sound character due to specific adjustments in the filter structure.
[13] The sonic differences noticed between the two models, 6581 and 8580, were attributed broadly to the nuances in the analog filters, and intrinsic design distortions.
These sound characteristics were heavily influenced by updates in the circuitry and quality differences in the material batches used in the various production runs of the chips.
[citation needed] The majority of games produced for the Commodore 64 made use of the SID chip, with sounds ranging from simple clicks and beeps to complex musical extravaganzas or even entire digital audio tracks.
[15] Most software did not use the full capabilities of SID, however, because the incorrect published specifications caused programmers to only use well-documented functionality.
[3] Well known composers of game music for this chip are Rob Hubbard, known for titles such as Commando, Monty on the run, International Karate, Sanxion, Skate or Die!, and Martin Galway, known for Wizball, Arkanoid and Times of Lore.
Other noteworthies include Jeroen Tel (Cybernoid, Turbo Outrun, Robocop 3 and Myth), Ben Daglish (The Last Ninja, Jack the Nipper, Firelord, Gauntlet), David Dunn (Finders Keepers and Flight Path 737), David Whittaker (Speedball, BMX Simulator, Glider Rider) and Chris Hülsbeck (R-Type, Turrican and The Great Giana Sisters).
The USHSC is based on both the SOASC= and HVSC, but also uploads recordings of recent SID music released at the Commodore Scene Database (CSDb) site.
[20] However, there are loaders like RealSIDPlay and converters such as PSID64[21] that make it possible to play a substantial portion of SID files on original Commodore computers.
