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View topic - FM+PSG on Mark III/SMS: is it possible or not?

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  • Joined: 10 May 2011
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FM+PSG on Mark III/SMS: is it possible or not?
Post Posted: Fri Mar 06, 2020 3:45 pm
Please help me on this, after all, the japanese BIOS can do it right? And Lost Stars, the voices are played back by the PSG or by the FM chip when we play the game on a modded SMS?

I have a brazilian SMS modded with etim board. When I play Altered Beast, for instance, I don't know if the voices are played back by the PSG or by the YM2413.

Thanks guys!
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Post Posted: Fri Mar 06, 2020 5:37 pm
Japanese SMS - can select one or both chips at the same time
Mark III - can only use one at a time
FM board - not sure, depends on the revision?

YM2413 can’t play samples.
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Post Posted: Fri Mar 06, 2020 6:37 pm
Maxim wrote
Japanese SMS - can select one or both chips at the same time
Mark III - can only use one at a time
FM board - not sure, depends on the revision?

YM2413 can’t play samples.


Thanks Maxim!

So only the MK-2000 can use at the same time, that's because of the japanese BIOS thing I guess? Is there any cartridge that uses PSG+FM simultaneously also that is known?

FM boards would depend of the revisions, because it's unnoficial, I get it.

So, after all, any voice I hear on a Sega Master System game on FM mode is indeed coming from the PSG, like Dead Angle, Altered Beast, etc.

Thanks again Maxim!
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Post Posted: Sat Mar 07, 2020 7:44 am
You might find this topic interesting. If you want to try the test ROM yourself, use the improved version some way down the page, not the one in the first post.

The YM2413 actually can play samples, but it hasn't been done on the Master System (yet).
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Post Posted: Sat Mar 07, 2020 7:57 am
All official games I had a look at switch between "PSG only" and "FM only" modes.

When playing music/SFX, the game enables FM and disables PSG. When a game (like Alex Kidd Lost Stars) has to play a voice sample, it temporarily turns off the FM chip and enables PSG sound.

The Audio Control Port wiki page documents the various modes.
Official games switch between mode 00 and 01, except for the JP BIOS, which uses mode 03.
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Post Posted: Mon Mar 09, 2020 3:45 pm
ValleyBell wrote
All official games I had a look at switch between "PSG only" and "FM only" modes.

When playing music/SFX, the game enables FM and disables PSG. When a game (like Alex Kidd Lost Stars) has to play a voice sample, it temporarily turns off the FM chip and enables PSG sound.

The Audio Control Port wiki page documents the various modes.
Official games switch between mode 00 and 01, except for the JP BIOS, which uses mode 03.


Thanks ValleyBell.

Is there any reason for any cart game not use the mode 03? Just the composers that chose not to use it at any game the PSG channels with FM for extra sounds on their music, we can assume that?

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Post Posted: Mon Mar 09, 2020 4:53 pm
Any Japanese game would want to be compatible with Mark III. Any western game would not target YM2413 anyway.

However, there’s a bigger reason: it would take more space and CPU. The music engine used in almost all Japanese games is a dual mode FM or PSG one. This is how games could support FM but still fall back on PSG for a Mark III with no FM Unit. It supports three channels plus percussion. Thus most games don’t make use of the full six channels of FM available.

To support both at once would require a significant upgrade to the music engine to support 9 channels plus noise and percussion, but it would still need to downgrade to just FM or just PSG for a Mark III. That is quite tricky.

For the Space Harrier BIOS music, they did something weird: they put an FM engine playing FM data, and a PSG engine playing PSG data, and just run two at once. This uses twice as much CPU, but then there’s no actual game to run.
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Post Posted: Mon Mar 09, 2020 8:03 pm
Maxim wrote
Any Japanese game would want to be compatible with Mark III. Any western game would not target YM2413 anyway.

However, there’s a bigger reason: it would take more space and CPU. The music engine used in almost all Japanese games is a dual mode FM or PSG one. This is how games could support FM but still fall back on PSG for a Mark III with no FM Unit. It supports three channels plus percussion. Thus most games don’t make use of the full six channels of FM available.

To support both at once would require a significant upgrade to the music engine to support 9 channels plus noise and percussion, but it would still need to downgrade to just FM or just PSG for a Mark III. That is quite tricky.

For the Space Harrier BIOS music, they did something weird: they put an FM engine playing FM data, and a PSG engine playing PSG data, and just run two at once. This uses twice as much CPU, but then there’s no actual game to run.


Thanks Maxim, it's perfectly clear now.

Would be too much work downgrading a full FM+PSG music to the PSG only. But, it's good to know that the Master System is technically capable just fine of that, just hasn't been done.

Would be great if someone someday on a homebrew game compose some FM+PSG music (maybe playing on a final credits scene, which demands less CPU, or the title screen -- something like that)!
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Post Posted: Tue Mar 10, 2020 7:44 am
Cosmonal wrote
Would be great if someone someday on a homebrew game compose some FM+PSG music (maybe playing on a final credits scene, which demands less CPU, or the title screen -- something like that)!

The test ROM (v2) from the thread I linked to earlier plays a tune on both chips sinultaneously, just like the japanese BIOS, but it's really just a little test and it hardly uses either chip to its full extent.
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Post Posted: Wed Mar 11, 2020 5:52 pm
Kagesan wrote
Cosmonal wrote
Would be great if someone someday on a homebrew game compose some FM+PSG music (maybe playing on a final credits scene, which demands less CPU, or the title screen -- something like that)!

The test ROM (v2) from the thread I linked to earlier plays a tune on both chips sinultaneously, just like the japanese BIOS, but it's really just a little test and it hardly uses either chip to its full extent.


Many thanks Kagesan! I tested APTest2.sms on my PowerBase Mini and it plays both chips.
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