Yamaha YM2612
Encyclopedia
Sound chip
A sound chip is an integrated circuit designed to produce sound . It might be doing this through digital, analog or mixed-mode electronics...
developed by Yamaha. It belongs to Yamaha's OPN family of FM synthesis
Frequency modulation synthesis
A 220 Hz carrier tone modulated by a 440 Hz modulating tone with various choices of modulation index, β. The time domain signals are illustrated above, and the corresponding spectra are shown below ....
chips used in several game and computer systems. Developed as a stripped-down version of the YM2608
Yamaha YM2608
thumb|right|Yamaha YM2608YM2608, aka OPNA, is a sixteen-channel sound chip developed by Yamaha. It's a member of Yamaha's OPN family of FM synthesis chips, and the successor to the YM2203...
, it lacks its larger sibling's ADPCM channel, Rhythm Sound System, SSG
General Instrument AY-3-8910
The AY-3-8910 is a 3-voice Programmable Sound Generator designed by General Instrument, initially for use with their 16-bit CP1610 or one of the PIC1650 series of 8-bit microcomputers...
components, and GPIO ports. It also includes a simplified sound mixer with integrated DAC. It was also available in CMOS
CMOS
Complementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...
form, as the YM3438, aka OPN2C. It was most notably used in the Sega Mega Drive/Sega Genesis
Sega Mega Drive
The Sega Genesis is a fourth-generation video game console developed and produced by Sega. It was originally released in Japan in 1988 as , then in North America in 1989 as Sega Genesis, and in Europe, Australia and other PAL regions in 1990 as Mega Drive. The reason for the two names is that...
game console and Fujitsu's FM Towns
FM Towns
The FM Towns system is a Japanese PC variant, built by Fujitsu from February 1989 to the summer of 1997. It started as a proprietary PC variant intended for multimedia applications and PC games, but later became more compatible with regular PCs...
computer series. As the YM3438, it was used by Sega in various arcade game
Arcade game
An arcade game is a coin-operated entertainment machine, usually installed in public businesses such as restaurants, bars, and amusement arcades. Most arcade games are video games, pinball machines, electro-mechanical games, redemption games, and merchandisers...
systems, including the Mega-Play, System 18, and System 32.
The YM2612 has the following features:
- Six concurrent FM channels (voices)
- Four operators per channel
- Two interval timerProgrammable Interval TimerIn computing and in embedded systems, a programmable interval timer is a counter which triggers an interrupt when it reaches the programmed count.- Common features :...
s - A sine-wave low frequency oscillatorLow frequency oscillationLow-frequency oscillation is an electronic signal, which is usually below 20 Hz and creates a rhythmic pulse or sweep. This pulse or sweep is often used to modulate synthesizers, delay lines and other audio equipment in order to create effects used in the production of electronic music. Audio...
- Analogue stereo output (most other contemporary Yamaha FM chips require a separate external digital-to-analog converterDigital-to-analog converterIn electronics, a digital-to-analog converter is a device that converts a digital code to an analog signal . An analog-to-digital converter performs the reverse operation...
chip) - For channel three, operator frequencies can be set independently, making dissonant harmonics possible. (Normally, they would have a simple relation like e.g. 2x or 3x relative to a common base frequency.)
- Per-channel programmable stereo sound (Left, Right, or both Left and Right)
- Patch compatibility with Yamaha DX/TX synthesizers
The major difference between the YM2612 and the YM2608 is the removal of the original accumulator-equipped
Accumulator (computing)
In a computer's central processing unit , an accumulator is a register in which intermediate arithmetic and logic results are stored. Without a register like an accumulator, it would be necessary to write the result of each calculation to main memory, perhaps only to be read right back again for...
sound mixer, which mixed together the 14-bit floating point output of the FM channels. Instead it uses a simpler time-division sound multiplexer
Time-division multiplexing
Time-division multiplexing is a type of digital multiplexing in which two or more bit streams or signals are transferred apparently simultaneously as sub-channels in one communication channel, but are physically taking turns on the channel. The time domain is divided into several recurrent...
, which first truncated the 14-bit channel output to 9-bits, then rapidly looped through outputting each channel. This truncating caused a "glitch" as the waveform approached the zero (neither positive or negative) point, known as the "ladder effect". External sound filtering circuitry was used to reduce some of the noise generated by the truncating and channel looping, reducing the sound quality even more.
Along with the mixer changes, the chip was stripped of its predecessor's SSG component, although its vestigial SSG envelope generator is still functional.
The sixth channel can act as a surrogate PCM channel by means of the 'DAC Enable' register, allowing the chip to play 8-bit PCM
Pulse-code modulation
Pulse-code modulation is a method used to digitally represent sampled analog signals. It is the standard form for digital audio in computers and various Blu-ray, Compact Disc and DVD formats, as well as other uses such as digital telephone systems...
sound samples. Enabling the register disables FM output for that channel. PCM data is written to the channel via an 8-bit register. The YM2612 does not provide any timing or buffering of the PCM samples, so all frequency control and buffering must be done in software by the host processor.
The YM3438, aka OPN2C, the CMOS form of the YM2612, changed the Channel 6 DAC output to the same 9-bit output in FM mode. The chip also had higher output impedance, requiring heavier external noise filtering circuitry but outputting louder sound. Sega used an improved version of the OPN2C for the Model 2 version of the Mega Drive/Genesis
Sega Mega Drive
The Sega Genesis is a fourth-generation video game console developed and produced by Sega. It was originally released in Japan in 1988 as , then in North America in 1989 as Sega Genesis, and in Europe, Australia and other PAL regions in 1990 as Mega Drive. The reason for the two names is that...
, without the bit-depth truncating seen in the original OPN2 and OPN2C.
Pinout
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Example circuit
An example schematic for the YM2612 can be found here.
See also
- Yamaha YM2608Yamaha YM2608thumb|right|Yamaha YM2608YM2608, aka OPNA, is a sixteen-channel sound chip developed by Yamaha. It's a member of Yamaha's OPN family of FM synthesis chips, and the successor to the YM2203...
- Yamaha YM2203Yamaha YM2203The YM2203, aka OPN , is a six-channel sound chip developed by Yamaha. It's the progenitor of Yamaha's OPN family of FM synthesis chips used in many videogame and computer systems throughout the 1980s and early 1990s...
- Sound chipSound chipA sound chip is an integrated circuit designed to produce sound . It might be doing this through digital, analog or mixed-mode electronics...
- VGM
- GYMGYMGYM is a sound format for the Sega Mega Drive/Sega Genesis.The name stands for Genesis YM2612, since the file contains the data stream sent to the Yamaha YM2612 sound chip in the console. The data is logged to a file through the use of emulators running a ROM image.The GYM format first appeared on...