MegaCD Redbook Audio Pop Issue

[ItalianGrandma]

I tried listening to a few minutes of several tracks from Ecco the Dolphin (USA) in the BIOS CD player and the issue seems way less frequent or noticeable compared to OP's recordings, but I think it did hear it very slightly a few times. I'm also using a CHD...not sure if that makes a difference. I also tested the title screen of Keio Flying Squadron and the "zoom into town" intro of Lunar - The Silver Star as mentioned by another poster....I didn't hear it in Keio Flying Squadron, but it did seem like I noticed a slight crackle at one point in Lunar and that's it.

Edit: Tried the first level of Ecco and just sat there in game and I think I may have noticed it a couple times ever so slightly. Again, it doesn't sound nearly as noticeable or as frequent as OP's recordings.

[rhester72]

Wait, so you get popping with the BIOS CD player with normal audio CD rips? I can't find any way to get the Ecco (1) CD to play just the music in the BIOS player.

[Deadsaint]

Wait, so you get popping with the BIOS CD player with normal audio CD rips? I can't find any way to get the Ecco (1) CD to play just the music in the BIOS player.

No, was testing with Ecco 1 and couple other games. After loading the cue on the core menu, press A, I believe, instead of start at the first bios screen, and it will open the CD player instead of directly starting the game. After that, jump track 1 which is the game data, and the music from the game will play (as long as it is redbook of course). Every game I tested like this had the popping, but some songs are harder to notice than others. Ecco music compositions makes it very easy to notice any kind of audio issue because of how clean it is.

[rhester72]

[I'm keeping all of the below that I wrote as I listened for reference, but I did indeed hear slight popping at the beginning of track 12! Interestingly, it's consistent...even if I rewind and listen to the exact same spot again, it still happens in the same place and way. Given our different experiences, I'm starting to question whether this disc really is a valid Redump issue...will check on that and report back.]

Reporting back...the CRC32 does indeed match the Redump set...but I'm still having a quite different experience from you (with no audio pop at all until WELL into the disc). I wonder what that means.

...and in the megapost of all random brain dumps, one more edit - I went ahead and listened to the rest of the disc because I like it. =) In my case, only track 12 (physical track 12, audio track 11) has very consistent, repeatable popping at the beginning of the track and again at roughly the midpoint. Given 5 different masters were ripped with the exact same result, I have to believe what I'm hearing is some sort of mastering error common to all discs and not the same thing you are experiencing.

---

Got it. (I never knew that trick from back in the day, and I had a Sega CD!)

Trying with Ecco 1 and a set of pretty powerful flat reference speakers, I can't hear any audio popping of any kind - everything is flawless (and by the way, the CD+G data loss was fixed some time ago, it's also perfect now). Just in case, I literally listened to the entire soundtrack end to end in case there could be variance at what point the popping occurs. My core audio settings:

Audio Filter: Model 1
CD Audio: Unfiltered
FM Chip: YM2612
HiFi PCM: No

The CHD I'm using is a confirmed-good rip:

chdman - MAME Compressed Hunks of Data (CHD) manager 0.228 (unknown)
Input file: Ecco the Dolphin.chd
File Version: 5
Logical size: 685,195,200 bytes
Hunk Size: 19,584 bytes
Total Hunks: 34,988
Unit Size: 2,448 bytes
Total Units: 279,900
Compression: cdlz (CD LZMA), cdzl (CD Deflate), cdfl (CD FLAC)
CHD size: 294,180,698 bytes
Ratio: 42.9%
SHA1: dec9f9d8cc7e9edafcd56b7b03023349dd0174f0
Data SHA1: b3d76d3a5bc0a07f1c7f716330d13dbb855caa74

One other thought...what sort of storage device is your CHD on? If the popping is normally at the start of any given track, I wonder if your storage is slightly too slow to keep up and the popping continues until it's had enough time to linearly buffer subsequent data. Mine is on my SD card, and I use SanDisk Ultra exclusively. (The only reason I doubt this being the case is that the sort of noise that results from underbuffer is NOT subtle or hard to detect, it is very obvious.)

Thank you for the question, by the way - I'd forgotten what a truly magical soundtrack Ecco has. It was a delight just listening to it straight through for the first time in decades! I also didn't realize that some musical arrangements (that are clearly part of the same composition) are split across tracks until I listened this way. laughs I wonder why they did it that way? I'm not aware of any limit on track length on CD audio.

[rhester72]

One other possible factor - I think the ARM CPU is what is used for CHD real-time decompression. Mine is overclocked to 1.2MHz (and has been since the very first alpha kernel became available)...not sure if that might be making a material difference. (I'll downclock later this evening and try again.)

[Deadsaint]

One other thought...what sort of storage device is your CHD on? If the popping is normally at the start of any given track, I wonder if your storage is slightly too slow to keep up and the popping continues until it's had enough time to linearly buffer subsequent data. Mine is on my SD card, and I use SanDisk Ultra exclusively. (The only reason I doubt this being the case is that the sort of noise that results from underbuffer is NOT subtle or hard to detect, it is very obvious.)

I tested with both the internal SD card (sandisk ultra, same as yours), as well as loading it trough the network with CIFS, from my PC. It is on a mechanical drive, but a pretty fast one with big cache and works well with all CD cores, even PlayStation. The popping happens regardless of which one.
For me the popping is completely random in both how loud it is on each channel and the exact moment it happens. It can happen louder on the right channel at 3 secs, or it can happen at both at 5 secs, there doesn't seem to be a pattern except that it happens more commonly at the beginning of the track, although it does happen in the middle, just way less frequently.
I'm using a redump version of the game in bin/cue format, so no compression, and I tested it with genesis plus GX core on retroarch on PC and the audio itself has no issue, it's crystal clear with no popping on the actual recording, the only popping I can get on the emulator is when pressing to skip to the next track.

EDIT: The popping seems to get worse and more frequent if, while listening to the music, I open the mister menu and start navigating it, even if I don't change any option, I was getting more frequent and louder pops, although still completely random and did not seem to match any specific action in the menu.

[Vicosku]

I'm still having this issue as well. I did switch to ethernet and server loading instead of SD like mentioned in my February post. I'm going to do some more in-depth testing again, but I wanted to mention that if I load the Ecco bin/cue in the PSX core (I have to boot with the miscellaneous option "CD Lid open") and then play tracks in the PSX CD player, I don't get any pops. Might be something for others with this issue to try. I Figure this would eliminate suspicion of an issue with the CD image used, at least.

I also want to mention I've played 8 hours of Lunar 2 recently. The non-Redbook audio tracks don't have any crackles or pops.

*Edit - Forgot I posted in February. Made updates in reference to it.

[Jingsing]

I can confirm this is still an issue for me too.

[Deadsaint]

An update on the issue: I heard a NeoGeo CD core is on the way and there was a test Mister binary that had changes to the CD code that is shared with MegaCD, so I joined discord to get it, but there was no difference. However, looking into the testbuild channel, I found a MegaCD build that was proposed to fix the Issue, I believe the same one that was posted on this thread by Aberu on June 25 2022, and lo and behold, that build completely fixed the issue for me. Some people were still having the issue even with that build, so maybe the fix was never incorporated in the main MegaCD core?
Not sure if there were other things outside the core itself on the MiSTer that could affect that, but whatever the case, for me at least, the issue is completely gone using that build.

[FPGA64]

The Neo Geo CD core uses the same code to access the CD as the Mega CD. So the addition was for that not the Mega CD. Discord has asked that people test the Mega CD using the new mister available on the discord to see if any issues have been created

[Deadsaint]

The Neo Geo CD core uses the same code to access the CD as the Mega CD. So the addition was for that not the Mega CD. Discord has asked that people test the Mega CD using the new mister available on the discord to see if any issues have been created

I see, I thought that maybe the issue was on that CD code shared with the NeoGeoCD, and during the new core development it might have been detected and solved, but I guess that wasn't the case. At least, as far as I tested, the new code didn't seem to have broken anything.

Anyone that was having issues with the MegaCD core sound, try downloading this build and see if it solves the issue. If it works for everyone, maybe the changes could be incorporated in the main MegaCD core from the update script.

Update: The latest MegaCD core released 23.02.24 still has the sound popping issue.

[Deadsaint]

Any further update on this issue?
Anyone that was having issues, did the modified build fix it?

[wark91]

HI,
If you have an account on discord you could join the mister discord to propose it on #test-build

[Deadsaint]

HI,
If you have an account on discord you could join the mister discord to propose it on #test-build

This modified build was posted on #test-build a year ago by birdybro, that's where I got it from, I just happened to find it when looking for a solution to the issue. For some reason the fix was never integrated to the main release of the core.

[wark91]

if it is not integrated maybe another issue block to be intergrated @birdybro if you recall ?

[paulbnl]

I will work on it. It needs some fixes which I also did for the NeoGeo CD.

[wark91]

Thank you paulbnl !

[Vicosku]

I noticed the test build on Discord yesterday. I played a bit of Ecco, Lunar, and about an hour of Popful Mail last night. So far I haven't been able to discern pops or crackles like before. Thanks so much!

[Deadsaint]

I will work on it. It needs some fixes which I also did for the NeoGeo CD.

Working perfectly now, no more popping, thank you so much!