YM2413

Yamaha YM2413 (OPLL)

Overview

The Yamaha YM2413, better known as OPLL, or informally "OPL Light," is a cost-reduced FM synthesis sound chip released by Yamaha in 1986. Rather than being a general-purpose FM chip like its relatives, the YM2413 was built from the ground up as a cheap, mass-producible option for consumer electronics manufacturers who wanted the recognisable sound of Yamaha FM synthesis without the cost of a full-featured chip like the YM3812 (OPL2).

The OPLL's core is essentially a stripped-down version of the YM3812, offering the same nine channels of two-operator FM synthesis, selectable between nine simultaneous melodic voices or six melody voices alongside five hard-coded percussion sounds. To keep manufacturing costs down, Yamaha removed a large number of the chip's internal registers, most significantly limiting the chip to just one user-programmable instrument at a time, with the remaining fifteen instrument voices, including violin, guitar, piano, flute, trumpet and several others, permanently hard-coded into the chip and impossible for the user to modify.

Despite this severe reduction in configurability, the YM2413 retained one small but musically useful advantage over its OPL/Y8950 relatives: it offers two selectable waveform types per operator rather than the single sine wave available on the plain YM3526, giving its fixed instrument set a bit more tonal variety than the raw specification might suggest.

The chip became the basis for the MSX-MUSIC standard, introduced by Panasonic in 1987 as a cheaper, though incompatible, alternative to the earlier Yamaha Y8950-based MSX-AUDIO standard. It was also used directly in the Sega Mark III and the Japanese Sega Master System via the FM Sound Unit expansion, as well as in various arcade boards from manufacturers like SNK and Alpha Denshi.

Technical characteristics

• Manufacturer: Yamaha
• Model: YM2413 (OPLL), 18-pin DIP package
• Channels: 9 melodic voices, or 6 melody + 5 percussion voices
• Operators per channel: 2
• Waveforms: 2 selectable per operator
• Instruments: 1 user-programmable instrument + 15 fixed, hard-coded instrument presets
• Percussion sounds: Bass drum, snare drum, tom-tom, top cymbal, hi-hat
• Interface: Simple 8-bit data bus with a single address line
• Related chip: Y8950 (MSX-AUDIO), shares the same FM approach but with ADPCM instead of dual waveforms
• Notable systems: MSX-MUSIC standard (Panasonic FM-PAC and later built into MSX2+/Turbo R machines), Sega Mark III / Japanese Sega Master System (FM Sound Unit), various SNK and Alpha Denshi arcade boards

Composing within fixed instrument limits

Composing for the YM2413 required working within an unusually rigid set of constraints compared to other FM chips of the era: since only one custom instrument patch could be defined at a time, composers largely had to build their music around the chip's fifteen fixed presets, reserving the single programmable slot for a sound none of the built-in instruments could adequately provide.

Because FM synthesis is not particularly well suited to producing convincing percussion sounds, the chip includes an entirely separate, purpose-built percussion module covering the basic elements of a drum kit, bass drum, snare, tom-tom, top cymbal and hi-hat, letting composers combine melodic FM instrumentation with recognisable, dedicated drum sounds rather than trying to approximate percussion through FM alone.

Despite its reduced flexibility, the YM2413's low cost made it an attractive option for manufacturers throughout the late 1980s, and its distinctive, somewhat "toy-like" but still clearly FM-derived sound became closely associated with specific platforms, particularly the Japanese Sega Master System library and MSX-MUSIC-compatible MSX software.

Legacy and importance

The YM2413 occupies an interesting niche in Yamaha's FM chip lineage: rather than pushing FM synthesis technology forward, it demonstrated how far the underlying architecture could be simplified and cost-reduced while still delivering a recognisably "FM" sound to consumer hardware. Its adoption by Panasonic for MSX-MUSIC created a lasting, if somewhat awkward, split within the MSX ecosystem between the incompatible Y8950-based MSX-AUDIO and YM2413-based MSX-MUSIC standards, a fragmentation that persisted throughout the platform's later years.

Today, the YM2413 remains popular among chiptune musicians and retrocomputing hobbyists specifically because of its low cost and simple interface, with modern DIY kits and expansion boards, including options for platforms like the RC2014 retrocomputer, letting hobbyists build their own YM2413-based music hardware using original chips.

Further reading

• Yamaha YM2413 overview (Wikipedia)
• MSX-MUSIC standard overview (MSX Wiki)
• The YM2413 FM OPLL, practical notes (waveguide.se)