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 Post subject: YMF271 emulation issues
PostPosted: 2021-09-29, 22:35:56 

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The YMF271 (OPX) sound chip emulation in MAME has been in a preliminary state for many years now. Especially envelope and timer emulation have very noticeably incorrect, when compared with real PCB or OST recordings.

Since the timer emulation is incorrect, and most games used the timers, the existing packs will need to be relogged even if the emulation improves.

Also, MAME's emulation of the YMF271 has actually regressed lately, which will introduce issues in other games when logged.

Hence, I think it's best that that the YMF271 packs are deleted from the main site. Since the packs could still potentially be useful for emulator development, they can still be archived somewhere. But considering that the packs won't ever sound correct, it's probably better that they aren't visible in the homepage.


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PostPosted: 2021-09-30, 5:43:53 
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Honestly, at this point, I don't know if we are ever going to have accurate YMF271 emulation without assistance from at least one of the people who originally designed that chip over 25 years ago, or a composer who had a fair amount of experience working with it back then. It is a testament to how advanced it was for its era that in 2021, emulation of it is still nowhere near 100%.

I don't know how many people have reached out to Yamaha over the years about getting more info on the YMF271 and I'm not sure where to begin as far as requesting a datasheet. The fact that one does not seem to have turned up on the Internet after all this time either indicates that one does not exist (and I strongly doubt that's the case), or that Yamaha is very protective of anything involving this chip (though I would imagine that by this point they should have little to no problem with the info becoming public knowledge, as the chip has long fallen out of mainstream use [and was never that popular or ubiquitous to begin with even in its time]).

As the MAME emulation has regressed, perhaps it may be helpful to identify the final version before the regressions were introduced, and encourage rippers to use that one for any future YMF271 rips (or perhaps even redo existing rips with it, assuming there were no major improvements from the MAME versions used for those rips to the final version without the regressions). I totally understand if the rips are pulled from the site completely and support for the YMF271 is dropped for the moment. This is just an idea so that it hopefully doesn't have to come to that. As always, I appreciate your efforts and those of everyone else...I listen to music on VGMRips.net every day, and couldn't imagine going a day without this site.


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 Post subject:
PostPosted: 2021-10-16, 1:57:01 

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You probably shouldn't have to worry about the sets being backed up since since every set on this site is probably already backed up on Joshw under the Hoot section. As for where regressions started, I think it was this commit:

https://github.com/mamedev/mame/commit/ ... 6b00890e17

When that was added, Bloody Roar music started having issues.

EDIT: I just checked the archive on joshw, it's very likely out of date and probably missing newer releases.


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 Post subject:
PostPosted: 2021-10-21, 16:51:17 

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cmccaff1 wrote:
Honestly, at this point, I don't know if we are ever going to have accurate YMF271 emulation without assistance from at least one of the people who originally designed that chip over 25 years ago, or a composer who had a fair amount of experience working with it back then. It is a testament to how advanced it was for its era that in 2021, emulation of it is still nowhere near 100%.

I don't know how many people have reached out to Yamaha over the years about getting more info on the YMF271 and I'm not sure where to begin as far as requesting a datasheet. The fact that one does not seem to have turned up on the Internet after all this time either indicates that one does not exist (and I strongly doubt that's the case), or that Yamaha is very protective of anything involving this chip (though I would imagine that by this point they should have little to no problem with the info becoming public knowledge, as the chip has long fallen out of mainstream use [and was never that popular or ubiquitous to begin with even in its time]).

As the MAME emulation has regressed, perhaps it may be helpful to identify the final version before the regressions were introduced, and encourage rippers to use that one for any future YMF271 rips (or perhaps even redo existing rips with it, assuming there were no major improvements from the MAME versions used for those rips to the final version without the regressions). I totally understand if the rips are pulled from the site completely and support for the YMF271 is dropped for the moment. This is just an idea so that it hopefully doesn't have to come to that. As always, I appreciate your efforts and those of everyone else...I listen to music on VGMRips.net every day, and couldn't imagine going a day without this site.


I have a Japanese version of the complete YMF271 data sheet here.
https://drive.google.com/file/d/1tb9oER ... sp=sharing


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 Post subject:
PostPosted: 2021-11-21, 2:42:23 
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To denjhang: thank you very much for your efforts! (And sorry for not responding sooner.)
This is absolutely fantastic information, and I'm grateful that an effort was made at an English translation.
The pictures seem to shed some light on how the FM engine works, or at least I got that impression.

If you don't mind, I've made backups of the zip file and sent a message to the MAME team using their official website's contact form.
I'm not sure how soon or even if I'll hear back, but I have a feeling this is going to be very useful towards improving if not completely perfecting the emulation of this complex Yamaha chip.


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 Post subject:
PostPosted: 2021-11-21, 22:49:42 

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the MAME team already has the full application manual (and not just the datasheet which only contains parts of the information).


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 Post subject:
PostPosted: 2021-11-22, 0:16:40 
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Ah, I see! Well, it was still a good opportunity to thank them for their hard work, so to me it wasn't time wasted.

It really says a lot about how complex this chip is that the MAME team basically has all the publicly available information on it and the emulation still isn't 100% accurate more than 15 years after support was first added for it.
It can't be chalked up to laziness because the emulation of many other sound chips is virtually flawless now and others are still being actively improved.
It's not like MAME is an on-again, off-again project...it's still being perfected and worked on.
After so many years I'm happy that MAME is still in active development.

At this point, I can imagine that the assistance of someone who helped to design and develop the chip will be necessary to ensure the emulation is improved.
The chip itself isn't even 30 years old, so most if not all of the original designers/developers should still be around to share their knowledge.
Lord only knows how many of them use social media, and better yet how active they are on it.


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