MOS Technology SID

The SID (Sound Interface Device) 6581/8580 from MOS Technology was the sound chip built into the CBM-II home computers, Commodore 64, Commodore 128 and Commodore MAX Machine from Commodore. It is a synthesizer/sound effects generator integrated circuit compatible with the 65XX family of microprocessors. The SID provides extensive and precise control of frequency, tone color (harmonic content) and dynamics (volume). Specialized control circuitry minimizes programming, facilitating use in low-cost video games and musical instruments. It was one of the first sound chips included in a home computer before the digital sound revolution.

The SID chip was created by engineer Robert Yannes, who later founded the synthesizer company called Ensoniq. Along with the VIC-II chip, the SID chip was instrumental in making the Commodore 64 the best-selling computer in history (it's even in the Guinness Book of World Records) and is partially credited with starting the demoscene. i>.

El CID tiene la Patente USPTO n.º 4,677,890, que fue solicitada el 27 de febrero de 1983 y concedida el 7 de julio de 1987. Expiró el 7 de julio de 2004.

Features

• Three oscillators: 0-4kHz range.
• Four wave forms per oscillator: triangle, saw tooth, variable pulse, noise.
• Three amplitude modulators (range: 48dB).
• Three envelope generators:

  Exponential response,

  Attack range: 2 ms - 8 s

  Decay range: 6 ms - 24 s

  Sustained levels: 0 - volume peak

  Relaxation range: 6 ms - 24 s.

• Synchronization of oscillators.
• Ring modulation.
• Programmable filter:

  Cutting range: 30Hz - 12kHz.

  12 dB/octave Rolloff.

  Departures of low passage, high, band and band removal.

  Variable resonance.

• Volume master control.
• Two A/D potentiometer interfaces.
• Random Number Generator/Modulation.
• External audio input.

Technical details

The SID chip is a mixed signal circuit offering digital and analog circuitry at the same time. All ports on the control are digital, but the output ports are analog. It offers three speech synthesis, where each voice can use one of four different waveforms: square wave (with variable pulse width), triangle wave, sawtooth, and pseudo-random noise (but not white noise), and certain complex waveform combinations. Each voice can use ring modulation with one of the other waves, e.g. the frequency spectrum is multiplied and taken out. Ring modulation, filter and programming techniques to switch between different waveforms at high speed make the characteristic sound of the SID chip.

Each voice can be passed through a common digitally controlled analog filter with variable cutoff frequency and resonance, which is constructed with the help of capacitors external to the circuit. An external audio input port allows external audio to be passed through the filter.

When setting the main output volume/gain on the 6581 using the 4 volume control bits, a click occurs at the output. This is proportional to the difference in volume, both positive and negative, and allows the possibility of playing with 4-bit digitized sounds on the Commodore 64 (digitizing/sampling must be done by external means, usually a simple sampler circuit connected to the 8 parallel bits of the serial/parallel port located on the expansion bus. This bug was used in several video games (probably for the first time in Ghostbusters, in which pressing the space bar everything stops but continues playing the word "Ghostbusters") and in many demos. The sounds produced are usually some words, but more often percussion instruments like drums and the like (the amount of sound that can be stored in a fraction of 64 kilobytes is very limited Additionally, it is CPU intensive, as it has to output samples very quickly (compared to the extremely slow CPU 6510), and can't do much more while a sample is playing. This "defect" is partially corrected by the 8580 used in the Commodore 64C and the Commodore 128DCR. This reproduces the digitized sound (samples) very low. Fortunately, the volume level can be restored by a hardware modification or by a soft trick that affects the pulse wave. The software hack generally renders a single voice temporarily unusable, although clever musical compositions can make this problem less noticeable.

The 6581 and 8580 differ from each other in several ways. The original 6581 was manufactured using the old NMOS process, which uses 12V DC to operate. The 8580 is made with the HMOS-II process that requires less voltage, 9V, and therefore the chip heats up less. The 8580 is also more durable than the 6581. Furthermore, a better separation between analog and digital circuitry realized in the 8580 makes this a chip with less noise and distortion. A simple hardware modification can be added to 6581-based computers to eliminate most of the noise, but this results in disabling the Audio-In function.

Sound in video games

Most games produced for the Commodore 64 used the SID chip, with sounds ranging from simple clicks and beeps to complex pieces of music or even full digital audio tracks. Due to the technical mastery required to implement music on the chip, and its versatile features compared to other sound chips of the time, Commodore 64 composers have described the SID as a musical instrument in its own right. However, most software did not use the full capabilities of SID, because incomplete published specifications caused programmers to only use well-documented functions. In contrast, some older computer programs relied on specifications, resulting in inaudible sound effects.

Some of the best-known composers of SID music for video games are Martin Galway, known for many games including Wizball, and Rob Hubbard, known for titles such as ACE 2, Delta, International Karate, International Karate Plus, and Monty on the Run. Other composers include Jeroen Tel (Cybernoid and Myth) and Chris Hülsbeck, whose compositions began at SID but have spread to any type of music on computers and synthesizers.

SID file format

A .SID file, also called PSID, is a sound data file that not only contains the note frames, but also the 6502 assembly code (also called player or player) needed to play the music on the SID. At first, a hardware device was used (usually in cartridge format for the Commodore 64/128) that caused a non-maskable interruption and allowed the part of the computer's memory that contained the music and the player to be dumped using a program resident in the cartridge. All current sounds are produced on a real SID chip or via a software emulator that emulates the SID chip. The High Voltage SID Collection contains more than 30,000 SID music. SID files have the MIME type audio/prs.sid

The SID file format is not a native format for the Commodore 64/128, but a specific format created by music players supported by emulators such as PlaySID and Sidplay. However, there are loaders such as RealSIDPlay and converters such as PSID64 that make it possible to play most SID files on original computers.