Sunday, April 12, 2015

GEEKSPEAK U: The Yamaha FM chips of Gaming - Part 8 of 12: YM2413 (aka OPLL)

OPLL is based on the OPL2, but stripped down for budget purposes. For one, it could only use two of OPL2's four waveform options - plain sine, or half sine, and not the absolute sine or quarter sine. For two, it was TDM, like the OPN2, rather than adder output (though I do not believe it suffered from the ladder effect).

Lastly, and perhaps most importantly, on ALL of these chips I've mentioned so far, OPM, OPN, and OPL you could custom set the channel parameters (operators, algorithms, etc) on EVERY channel on that chip. On the OPLL, of the nine (or six) instrument channels, only one...ONE was completely user definable. The other channels had to use "canned", or pre-programmed instruments (such as flute, acoustic bass, guitar, brass, etc).

There were 15 canned voices that programmers could choose from, and that was what they had to work with. Granted, the voices sounded nice...but still they were canned instruments, with only one definable custom voice at any one time. As a result, OPLL music is going to sound a LOT more samey than any of the other FM chips.

That's a huge limitation for OPLL! Even with OPL only being able to use plain sine, OPL, as "vanilla FM" as it is is still generally regarded to be the more all-around usable, powerful chip because of the user definability of all its channels. Though, to me, the listener, I still think OPLL sounds more robust than OPL due to it's ability to use half-sine operators. It sounds more like OPL2 to me than OPL.

I guess I'll let you decide for yourself. :-)

OPLL did see some use in the Arcade (though I don't believe it was ever used by itself, but in conjunction with, say, the OPN), and it was also used in an FM music making cart for the MSX called the MSX Music. There was also MSX Audio which was considered the more powerful format, and featured OPL instead of OPLL. But most likely its most famous use was in the Japanese Sega Mastersystem. The Japanese Mastersystem had the OPLL built in as well as the global Mastersystem's PSG chip, the Texas Instruments SN76489. None of the other region's Mastersystems had the OPLL built-in (though there is an aftermarket mod kit that will add it to the other regions).

The relationship between FM and PSG on the Mastersystem is different than the relationship between FM and PSG on the Genesis. On the Genesis, the PSG supplements the FM, and all Genesis games (except Frogger) use the FM, but several choose to supplement it with PSG, bringing sound channels to 10 from 6. Well, in the case of the Mastersystem, it's either or, rather than both / and.

Many games have no instructions for FM, and will run PSG in any region. The ones with instructions for FM also have instructions for PSG, but they won't run simultaneously, instead, it will check for the presence of the OPLL, and if found, will play FM. If not found, it will revert to PSG (this is why the FM mod on, say, the US Mastersystem will be effective, because even the US version of those games still have the FM code in them, they just revert to PSG when the FM chip is not found).

The only exception to this is not a game, but the BIOS screen to the JP SMS, if turned on without a game plugged in, it'll play a track from Space Harrier, but modified to feature FM and PSG working in concert, like you'd hear on the Genesis. This implies to me that it's not an actual hardware limitation in the system as I had suspected. I suppose it's so the game will work seamlessly in any region without requiring reprogramming.

If anyone knows of any actual Mastersystem games that actually do use FM and PSG in tandem, please let us know in the comments.

The Konami VRC7 chip is based on the YM2413, but there are enough differences between it and a stock OPLL that we can consider it a distinct chip, and thus, it shall receive its own part in the series.

I'll share some OPLL examples from the Mastersystem, as well as the MSX Music. And for cross-reference, I'll share both the FM and the PSG versions of the Mastersystem R-Type soundtrack.

For starters, here's the FM version of R-Type

Now, here's the PSG version - this is running on the Texas Instrument SN76489 PSG chip that is common to all regions of the Mastersystem (and is also the exact same PSG chip used in the Genesis for its PSG - a modified for stereo version of it can be found in the Game Gear handheld)

One more comparison while we're at it, The Aleste soundtrack - only this time not Mastersystem FM vs Mastersystem PSG, but rather Mastersystem OPLL vs MSX Music OPLL. The MSX version sounds much beefier and fuller, while the Mastersystem version sounds thinner and scratchier. I don't know if this is an accurate reflection of the difference from system to system, or just the quality of the YouTube video. More investigation is required on my part, and if I find anything interesting, I may post a blog about it in the future.

Meanwhile, here's the Mastersystem version

Here's the MSX: One difference I do notice is that the MSX version is getting some percussive help here and there from the MSX's stock PSG chip, while the Mastersystem version is depending entirely on the FM chip. I don't believe this wouldn't account for any of the differences I mentioned above, but it is a difference to notice.

There were different carts with the MSX Music designation. While they all had the OPLL as the common denominator, and while they all had access to the MSX's stock General Instruments AY-3-8910 PSG, they differed in various other ways. Some even included the ability to use PCM percussion! As far as how this FM/PCM/PSG MSX2 sound system would stack up to say, a Sega Genesis, it's an interesting question. The FM chip in the Genesis is substantially superior to the FM chip found in the MSX, but the PCM quality is significantly better than the DAC sampler on FM channel 6 in the Genesis (and the MSX PSG is slightly better than the PSG the Genesis uses as well.) I'd still give the crown to the Genesis on account of the FM chips. But it's a real question, worthy of real discussion.

Once again, I'll let you decide for yourself. Here are Xak 1 and 2, and Xak: The Tower of Gazzel (presumably Xak 3.) For some reason, the Xak 2 soundtrack does not use PCM percussion, but 1 and 3 do.

As alluded to earlier, here's the OPLL/PSG duet JP BIOS version of the Space Harrier theme

And lastly, I'll just leave you with two random tracks from the Mastersystem...just because.

Galaxy Force - Beyond the Galaxy (in my opinion, the best Mastersystem use of the OPLL of everything I've shared here.)

Double Dragon - Stage 2

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