Monday, April 6, 2015

GEEKSPEAK U: The Yamaha FM chips of Gaming - Part 1 of 12: Introduction + OPM (YM2151)

While Yamaha had several lines of chips that either "were", or at least "had" FM, for pre-fifth generation gaming, only three lines were used, OPM, OPL, and OPN. Each chip had a chip name, and then a name identifying what series it was from, and its relation to the rest of the series.

The OPM "series" was not really a series, as it only had one chip, the YM2151....and it's series identifier....wait for it, waaaaaiiit for it: "OPM".

While there were several FM chips used in arcade games, this one was the most prolific, and probably the most powerful. This chip had limited use outside the arcade, as it was the principle chip used in the Sharp X68000, but for the most part, this was an Arcade chip.

It was an eight channel chip, each capable of up to four operators, and eight algorithm settings. It also had some special features, such as a secondary detune parameter, and an advanced LFO. It could only use sine wave operators (except for the LFO, which could use any basic waveform as well as noise), and did not have ANY sampling, or PSG capability. This wasn't a big problem though, since A) it was almost always paired with a sampler chip in the arcade, usually something from either Okidata's MSM line, or Sega's proprietary "SegaPCM" - the Sharp using an MSM, and B) it didn't really need PSG either since 1) FM can "fake a square wave" with two sine waves very convincingly, and 2) it had enough total channels that it could spare some to fake PSG, and still have enough for more serious FM applications.

Here's an example of the OPM - Shinobi (Arcade) Soundtrack:

Shinobi PCB had OPM and a sampler chip, but the sampler was used for voice clips and sound effects. As for the music: 100% pure unadulterated OPM FM!

And here are a few other examples for you (a mix of complete soundtracks and stand alone tracks) - all using the YM2151 OPM from either the Arcade, or from the Sharp X68000 (some also use PCM sampling for percussion, and some are pure FM). If you have any others you'd like to share, feel free to post away in the comments!

Akumajou Dracula (aka Castlevania) - X68000 OST - Load BGM

Area 88 (aka UN Squadron) - Arcade - Complete OST

Metal Orange EX - X68000 - Stage 1 Theme

Marble Madness - Arcade - Full OST

and lastly - Shadowland - Arcade - Full OST


  1. I bought lately the OPM based sound module for my MSX computer and i should say this is very, really powerful sound chip! Thank you for spreading the word about it, it is less known than OPL chips, i think it has been underestimated or so

    1. Ah! Thanks for your comment, Pencioner!

      Yeah, the OPM is an amazing chip! The King of the Arcade, for sure!

      The only thing it lacks against the otherwise inferior OPN series chips is SSG Envelope. Listen to the deep echoing bass in Stage 1 from Streets of Rage 1 (aka "Fighting in the Streets") and then look up the OPM video where someone just input the OPN code straight into the OPM, and you'll hear SSG EG in full its stark absence on the OPM rendition.

      Now, confession: I knew about MSX Audio and MSX Music, based on the OPLL and OPL, but I don't remember hearing about an OPM based MSX Module. Can you tell me more about it? :-)