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  • Joined: 22 Apr 2018
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Game Gear Cartridge FM Audio?
Post Posted: Mon May 04, 2020 5:08 am
Has anyone tried to generate SMS FM audio in the cartridge and inject it through the TVL and TVR audio lines of the Game Gear cartridge connector?

The Game Gear has left and right audio inputs for the TV Tuner, but they work outside of TV Mode too. They still work even on McWill-modded Game Gears.

If my naïve assumptions are correct, it should be possible to make something like a Game Gear EverDrive with an embedded FM audio simulator in an FPGA and enjoy the enhanced sound tracks of those games that have one.

You might wonder why I believe it's possible. I did a potentially foolish thing: I tried covering the "\TV" pin of the TV Auto Tuner with nonconductive tape to leave the Game Gear in regular "Game Gear" mode rather than TV mode (confirmed as the unmodded Game Gear no longer displayed the video signal from the tuner's A/V connector), and noticed the audio I'm feeding in to the TV Auto Tuner's A/V connector was still audible. When I removed the tape and tried again it was back to regular TV mode, displaying the image too.

What I don't know yet is how it sounds when both Game Gear PSG and expansion port are producing audio, but luckily most SMS games with FM audio were developed for the Mark III which didn't permit these to coexist anyhow so I suspect it might work out fine.
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Post Posted: Mon May 04, 2020 10:04 pm
Viletim confirmed in an old post somewhere that his FM board it's supposed to work with the Game Gear. It's missing two signals though, one can be generated pretty easily (!KB SEL, IIRC) but one of them cannot.

However the second one is only necessary for a couple of games to work with the FM sound and could be patched.

I've not tried this myself, just going off of memory from the thread.
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Post Posted: Wed Jul 01, 2020 5:21 am
I have been looking at this a bit today and it seems like it should work out fine.

The audio inputs on the cart slot feed in through some caps and mix into the psg audio outputs through some resistors. Then its fed over to the audio board.

Im working on some other stuff at the moment and need to build a breakout board for the game gear so ill test this and see how it goes.

The only thing it wont be able to do is switch the psg sound on/off like it does on the jp master system as obviously that sound signal is not fed out through the cart connector. The DB electronics power base fm adapter for the genesis/megadrive will have the same issue. I believe only a few games are effected by that so its probably not a big deal anyway.
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Post Posted: Tue Aug 11, 2020 7:03 am
Finally got my right angle edge connectors from china that i needed to make an SMS FM board fit onto my break out board/extender.

I can happily say that you can indeed put FM hardware onto the cart port and inject the audio in through the tv tuner audio inputs. No reason that you couldn't shrink it all down and include it into a game/flash cart. I only tested this on a 2 ASIC game gear but i imagine it would work fine on a 1 ASIC game gear also.

Two things won't work though.. region changing and audio mixing/switching using the FM hardware.

The game in the picture is actually an ever drive, it just happened to be a sonic shell that i used and never bothered to remove the label.

https://youtu.be/duvpsR2PPes
20200811_160420.jpg (156.19 KB)
20200811_160420.jpg
20200811_160425.jpg (120.35 KB)
20200811_160425.jpg

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Post Posted: Tue Aug 11, 2020 7:56 am
That's excellent progress, OPLL on Game Gear! For region checks should it be sufficient to either patch the game or use a Japanese Game Gear? SMSTestSuite correctly identifies their region

And is it true that most games don't use FM and PSG simultaneously anyhow in order to work on Mark III with external FM unit?
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Post Posted: Wed Aug 12, 2020 12:26 am
The region of the game gear can be changed.. one of the pins on the asic sets it if i remember correctly. I assume it works in sms mode too?

I dont think many, if any, games used both psg and fm at the same time. The jp bios uses both though.
I believe the audio switching on these fm boards left the psg enabled and switched the audio path off using a writeable register for the switch... there is a thread about this somewhere. From memory only a couple of games required it.
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Post Posted: Wed Aug 12, 2020 6:49 am
Only the Japanese BIOS uses both chips at the same time because it’s the only software that did not need to be compatible with the Mark III + FM Unit. Some games switch chips, to play samples on the PSG.
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Post Posted: Thu Aug 13, 2020 12:03 am
Maxim wrote
Some games switch chips, to play samples on the PSG.


Do you know off hand which ones do this?

I tested this adapter on a 1 asic game gear and it works fine on that too. The sound is a bit noisy but im not surprised given how ive got it hacked together.
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Post Posted: Thu Aug 13, 2020 7:14 am
Games with both FM and samples:

https://www.smspower.org/Games/Index?action=search&q=links%3D%2BTags.FM%2C%2...

After Burner
Alex Kidd: The Lost Stars
Alien Syndrome
Altered Beast
California Games
Captain Silver
Galactic Protector
Golfamania
Great Golf
Miracle Warriors: Seal of The Dark Lord
Nekkyuu Koushien
Shinobi
Space Harrier 3-D
Tennis Ace

Alex Kidd: The Lost Stars comes to mind as one where you can quickly and easily get the samples to play.
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