Sega CD audio heavily garbled over analog

[Cyber Akuma]

I was using headphones with my MiSTER Pi and noticed that the audio during Sega CD games was horrible. It varied from game to game, some it didn't happen, most it was very scratchy, and on many it was so garbled that it was completely incomprehensible if not just completely cut out. The audio was fine coming out of HDMI, but the analog audio from the 3.5mm jack was heavily scratchy. I tried adjusting all the audio settings but it made no difference, the only thing that made a difference was for some weird reason turning on the Composite Blend filter. I have no idea why a video filter that blurs the image was effecting audio but it seemed to fix 99% of the issue (I could still swear I could hear the occasional crackle, but that might be placebo at that point). The Sega CD core is the only core out of the dozens I tried where this happens too, none of the others gave me problems, even the PSX core despite that having initially had audio problems over analog on the MiSTER Pi.

Out of the games I tried Keio Flying Squadron was the worst, the intro was so bad it was completely incomprehensible and sounded like it was being spoken by a drowning robot, the audio was just as bad in-game. Robo Aleste started out ok but them became very bad as well. Sonic CD had the intro heavily scratchy, but when I got in-game was not as bad but still pretty messed up, and Lunar only had it happen occasionally. It never seemed to happen during the SegaCD boot intros.

Anyone have any idea about this? Or what could even be the cause? I can't even tell if this is a hardware or software issue, the fact that it mostly goes away when I toggle a video filter makes me think it's an audio issue, but if that was the case it should be happening to everybody, and when I tried to look it up I could only find a Reddit port from a month ago of a few people who experienced the same issue, all with a MiSTER Pi.

[DuaneDwayne]

I’ve seen several people mention this issue on both Reddit and Discord but I don’t know if they’ve determined if it’s a framework issue or hardware design with the new IO boards. I also experience it, but I’m not using any Mister Pi hardware. I have a DE10-nano, a 9.2 IO board from misterfpga.co.uk, and 128 MB SDRAM v2.9 from MisterAddons.

I haven’t been playing much Sega CD but people say the best test is in the Sonic CD intro or the first level of Shadow of the Beast 2. I hear the same garbled audio in those tests.

Personally, I’ve only seen this issue on the Sega CD core when using HDMI for video and analog audio. I don’t have this problem with analog video with analog audio, or HDMI video with digital audio. I don’t know if it’s related to your test, but I was using MisterAddons’s Y/C encoder outputting composite video and didn’t hear the garbled audio in Sonic CD’s intro.

[FoxbatStargazer]

Taki said his A/V board is a reproduction of 9.2 schematics and treats it like an official board, including going out of his way to credit sergey when his manufacturer failed to. Maybe the core has not been fully updated for 9.2? I recall some cores not even giving analog out at all until they got updated.

How do you "not use" the HDMI for video? Do you mean having no HDMI cable plugged in gives a different result?

[DuaneDwayne]

Taki said his A/V board is a reproduction of 9.2 schematics and treats it like an official board, including going out of his way to credit sergey when his manufacturer failed to. Maybe the core has not been fully updated for 9.2? I recall some cores not even giving analog out at all until they got updated.

How do you "not use" the HDMI for video? Do you mean having no HDMI cable plugged in gives a different result?

I just have the HDMI display turned off, but the cable is still plugged in. I always keep an HDMI and VGA cable plugged in because I like to use different displays depending on the core (handhelds I like to use HDMI for the filters and scaling, for consoles I use a CRT). So depending on what I'm playing, I just keep the other display off.

[TheJesusFish]

Analog audio corruption with the new 9.2 board affects a couple of cores, unfortunately. Taki did some tests and found that it affects 9.2 boards based on sorg’s design (so not misteraddons’ analog pro). There also seems to be an aspect of the silicon lottery with this too as some folks have no trouble, some folks have trouble with PSX, and some with GBA. The amount of corruption also seems to vary as well.

The Parasite Eve Intro on PSX and Shadow of the Beast 2 on Mega CD are what most folks have trouble with.

[FoxbatStargazer]

Taki said his A/V board is a reproduction of 9.2 schematics and treats it like an official board, including going out of his way to credit sergey when his manufacturer failed to. Maybe the core has not been fully updated for 9.2? I recall some cores not even giving analog out at all until they got updated.

How do you "not use" the HDMI for video? Do you mean having no HDMI cable plugged in gives a different result?

I just have the HDMI display turned off, but the cable is still plugged in. I always keep an HDMI and VGA cable plugged in because I like to use different displays depending on the core (handhelds I like to use HDMI for the filters and scaling, for consoles I use a CRT). So depending on what I'm playing, I just keep the other display off.

Can't replicate on my Mister Pi, even switching HDMI to direct video. I get garbled audio in Keio no matter what.

Maybe this has something to do with DE10-nano's CEC power weirdness? Are you not blocking CEC?

[Cyber Akuma]

Does Taki already know about this? Wasn't sure who I would even be trying to contact about this, Taki or the author of the MegaCD core since I have no idea if the problem is in the board or the core. I don't even now where to contact them, the issues tab in the github repo for the core only has one page of open issues that go back to 2020, or where for Taki.

I’ve seen several people mention this issue on both Reddit and Discord but I don’t know if they’ve determined if it’s a framework issue or hardware design with the new IO boards. I also experience it, but I’m not using any Mister Pi hardware. I have a DE10-nano, a 9.2 IO board from misterfpga.co.uk, and 128 MB SDRAM v2.9 from MisterAddons.

A single reddit post was all I found, though Google can't search through Discord (personally not a fan of so much knowledge being locked behind it lately).

I also saw mention though on that reddit thread that it might be the 9.2 board that is the problem, not the MiSTER Pi, but then if that was the case wouldn't this be much more widely reported as it would effect far more people than just those with a MiSTER Pi?

Though that thread also talked about it being the core itself that is the problem considering the weirdness of enabling a video filter mostly fixing it. Those video filters are done software-side, right? Nothing to do with the I/O board?

I haven’t been playing much Sega CD but people say the best test is in the Sonic CD intro or the first level of Shadow of the Beast 2. I hear the same garbled audio in those tests.

Yeah, I heard it in the intro of SonicCD too as I mentioned, not familiar with Shadow of the Beast 2, but I feel that Keio Flying Squadron was a far better test than Sonic. Sonic's audio is very clearly scratchy but still understandable, reminds me of when a AUX jack is not making a good connection when you spin the connector, while Keio's intro is completely incomprehensible.

Personally, I’ve only seen this issue on the Sega CD core when using HDMI for video and analog audio. I don’t have this problem with analog video with analog audio, or HDMI video with digital audio. I don’t know if it’s related to your test, but I was using MisterAddons’s Y/C encoder outputting composite video and didn’t hear the garbled audio in Sonic CD’s intro.

Yeah, I was using HDMI out for video (I guess technically audio too) when doing this test, but I tried launching a game in the Sega CD core then unplugging the HDMI cable before it was done loading and only listening through my headphones, issue was still there even with no HDMI connected.

How do you "not use" the HDMI for video? Do you mean having no HDMI cable plugged in gives a different result?

I just have the HDMI display turned off, but the cable is still plugged in. I always keep an HDMI and VGA cable plugged in because I like to use different displays depending on the core (handhelds I like to use HDMI for the filters and scaling, for consoles I use a CRT). So depending on what I'm playing, I just keep the other display off.

I am not an expert on this subject mind you, but a HDMI device should be able to tell if it's plugged into another HDMI device even if it's powered off, pretty sure the ID chip is powered by the connection even if the screen is off. I have a PC I remote into that I have to leave a monitor plugged in even if it's not powered on in order to get an image in Windows otherwise I get a blank screen. I ordered dummy HDMI plugs for that reason, they are nothing more than a HDMI port connected to a ID chip claiming it's plugged into a display resembling one of those slim-fit USB drives, I have a few for DisplayPort too, you can get them for less than a dollar.. (Kinda wish I could find 1080p ones though, all of them are 4K, which leads to some annoyances when remoting in with a 1080p screen as most of my tvs and all my monitors are)

Analog audio corruption with the new 9.2 board affects a couple of cores, unfortunately. Taki did some tests and found that it affects 9.2 boards based on sorg’s design (so not misteraddons’ analog pro). There also seems to be an aspect of the silicon lottery with this too as some folks have no trouble, some folks have trouble with PSX, and some with GBA. The amount of corruption also seems to vary as well.

Which cores? I know that the initial launch of the MiSTER Pis that the 9.2 board included with them had problems with PSX games, but that the board had been revised since then (apparently two of the capacitors were of the wrong value). But in that case IIRC no setting or option changed anything, in this case 99% of the issue is resolved with enabling a video filter, which is very weird (also if you are outputting to a CRT I assume you would NOT want to enable the filter that tries to blur it like component would, so this is not a great "fix" anyway) and makes me wonder if it's another hardware issue like PSX was or if this one is purely software.

The Parasite Eve Intro on PSX and Shadow of the Beast 2 on Mega CD are what most folks have trouble with.

I just tried listening to the Parasite Eve 1 and 2 intros through HDMI and my headphones at the same time and didn't hear anything wrong. Was Parasite Eve from back when the wrong capacitors were used in the first productions of the 9.2 board?

Can't replicate on my Mister Pi, even switching HDMI to direct video. I get garbled audio in Keio no matter what.

Maybe this has something to do with DE10-nano's CEC power weirdness? Are you not blocking CEC?

Garbled audio in Keio no matter what? Even if you enable the Component Blend filter?

[DuaneDwayne]

I just did some further testing and I'm more confused because now I don't experience it, at least for now. Maybe it was fixed somewhere recently? First, no I'm not using any CEC stripping or blocking. I'm just running an HDMI cable to a monitor and sending analog audio out to some basic Logitech speakers.

At first I thought maybe it was caused by CD access times combined with my storage device. I have all my games on a 256 GB SD card plugged into a USB-to-SD card adapter plugged into my USB hub v2.1 from MisterAddons. I'm using a 5V 5A Meanwell power supply with an inline switch from misterfpga.co.uk. I haven't had any issues on any core or game with this setup.

So I thought to copy Shadow of the Beast 2 and Sonic CD to the micro SD card the OS is installed on thinking that's faster. I booted up the MegaCD core and didn't have the audio issue in either game so I thought that was the problem. Then I rebooted the core and selected the games from the SD card over USB and I still don't get garbled audio anymore.

[FoxbatStargazer]

Alright so far I can fix the audio in Keio and Shadow in the following separate ways:

1) Turn on composite blend in the core options.
2) Set vga_scaler=1. (Tried a lot of resolutions and filter settings, audio is still pure no matter what.)
3) Change vga_mode to anything other than RGB
4) In shadow, sometimes opening the Mister menu is enough if I'm positioned correctly.

I suspect there's some kind of interference between the analog video and audio output. I've also separately noticed trouble holding analog sync at 1080p+ RGBHV with vga_scaler in any core, I bet there's some kind of vague relationship.

[Cyber Akuma]

Someone linked me to this: viewtopic.php?t=8479

Which is a bit of a rabbit hole that links to more previous threads but the gist of it from what I understood is:

• In September people were reporting issues with the audio from MiSTER Pi's headphone jack, mostly from PSX games.

• People suspected it was an issue with the 9.2 I/O board itself

• rickdangerous from Ultimate Mister mentions how their boards are not effected and it's purely a defect with Taki's version, which used 22000 caps in two places that should have been 2200 (Taki had since confirmed this was the defect and RMAed them)

• In October there is another post about this same SegaCD issue, mostly mentioning the same games I mentioned as some of the worst examples, and also talking about the Composite Blend tending to fix it

• There is debate on if it's the fault of the core or Taki's 9.2 boards

• One of the posters said that Taki told them it a fault of the cores not being compatible with 9.2 in general and they need to be updated

• Another poster says that the framework to support the new I/O boards was done months ago, including apparently on the MegaCD core

• Another poster says that they have a 9.2 board that's not a MiSTER Pi and don't have the issue

And... that's it. This was last October and didn't really seem to go anywhere. It's now January and the issue is still here and there isn't even a good idea on if it's a fault of the core or the boards, and if it's all 9.2 boards or just Taki's like it was when the PSX cores had garbled audio.

Getting a little worried that this is never going to get resolved if it's been months and seems to have gone nowhere.

Alright so far I can fix the audio in Keio and Shadow in the following separate ways:

1) Turn on composite blend in the core options.
2) Set vga_scaler=1. (Tried a lot of resolutions and filter settings, audio is still pure no matter what.)
3) Change vga_mode to anything other than RGB
4) In shadow, sometimes opening the Mister menu is enough if I'm positioned correctly.

I suspect there's some kind of interference between the analog video and audio output. I've also separately noticed trouble holding analog sync at 1080p+ RGBHV with vga_scaler in any core, I bet there's some kind of vague relationship.

Thanks for doing this testing, definitely confirms it's something to do with the video interfering with the audio somehow, though now I am more confused on where the problem lies, if there is some sort of cross-talk or something on the I/O board in certain video modes that messes with the audio or if it's just simply a bug in the core's code. Nobody seems to have looked into this that much since October, I bet it was even an issue in September but was overshadowed by the similar issue with the PSX core.

[FoxbatStargazer]

Maybe "fix" is too strong. Keio is vastly improved with say ypbpr but there's still minor pops. And I can make it much worse playing with the gamma correction, like max constrast boost. It all seems to boil down to video settings that affect the analog output only.

For a lark I tried the PSX core, and with ypbpr there are terrible pops even in the bios bootup, and a in a game like Diablo. Nearly vanished going to RGB.

I suspect the different analog video settings people might use is massively confusing the reporting around it.

[DuaneDwayne]

Maybe "fix" is too strong. Keio is vastly improved with say ypbpr but there's still minor pops. And I can make it much worse playing with the gamma correction, like max constrast boost. It all seems to boil down to video settings that affect the analog output only.

For a lark I tried the PSX core, and with ypbpr there are terrible pops even in the bios bootup, and a in a game like Diablo. Nearly vanished going to RGB.

I suspect the different analog video settings people might use is massively confusing the reporting around it.

I think this is it since we're all likely using different video output settings. I just tested again with "vga_mode=rgb" and I get the horrible audio with analog audio and HDMI video. I changed it to "vga_mode=svideo" and rebooted and now the audio is clean in Shadow of the Beast 2, Sonic CD, and Keio Flying Squadron, however I don't have the issue with Parasite Eve with either video setting. I also noticed bringing up the menu during garbled audio in Shadow of the Beast 2 made the audio cleaner, but the other games didn't do the same.

[Cyber Akuma]

So, I posted about the issue on GitHub, and birdybro tried compiling some test builds to see if they sounded better. The build did sound considerably better but I definitely still heard the occasional scratch/pop in the audio, reminds me of the normal version of the core when you turn composite blend on. Sounds significantly better, but the pops are still there, unless I am just hallucinating them at this point from having re-listened to them a few dozen times over this:

https://github.com/MiSTer-devel/MegaCD_ ... issues/112

On a slightly related note, since this is the first time I had manually installed a beta version of a core, is there any easy way to switch between versions of the same core? When I put the rbf file in the console cores folder it basically took the place of the original MegaCD core, is there an easy way to either list or switch between both so I can compare them easier?

I think this is it since we're all likely using different video output settings. I just tested again with "vga_mode=rgb" and I get the horrible audio with analog audio and HDMI video. I changed it to "vga_mode=svideo" and rebooted and now the audio is clean in Shadow of the Beast 2, Sonic CD, and Keio Flying Squadron, however I don't have the issue with Parasite Eve with either video setting. I also noticed bringing up the menu during garbled audio in Shadow of the Beast 2 made the audio cleaner, but the other games didn't do the same.

Yeah, considering it seems to be tied to analog video settings it's definitely compounding the issue that people are using different settings/displays that effect how good or bad the audio issue becomes.

That might also explain why opening the menu in Shadow of the Beast 2 effects it for you, and why it can vary on different parts of a game, it might be possible that even the image itself that's being sent out can cause it, not just the settings.

[Cyber Akuma]

Doing some additional testing, it's definitely effected by what is currently being displayed on the screen, and I don't just mean the composite blend. Two games that I found were good examples of this in opposite ways were Popful Mail and Shadow of the Beast II, I also experienced the behavior where opening the menu effects it that others mentioned here.

In the case of Popful Mail in the intro it first starts out sounding fine, but then gets heavily distorted. I realized that the screen when the intro first starts is almost entirely black, and the parts that are not are showing darker/grey colors. It wasn't until brighter colors started appearing in the intro that the audio started to distort. Furthermore opening the menu actually made the effect worse, so much so that it was still pretty badly distorted even with Component Blend enabled while the menu was open.

Shadow of the Beast II was almost the opposite. There was distortion in the intro, but what was interesting was when I got in game. In this one, opening the menu made it better, not worse, and I noticed that the audio was pretty distorted when I first load into the game standing near a tree, but if I walk left a little to make the screen scroll the effect diminishes greatly, walking back to the tree brings the distortion back. And again, Component Blend mitigated it heavily but it was still an issue.