Dreamcast gdemu ossc and dsc 301 brief image drop sound loss

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Guile
Posts: 145
Joined: Sun Jan 03, 2021 10:11 pm

Dreamcast gdemu ossc and dsc 301 brief image drop sound loss

Post by Guile »

I just installed a gdemu and I noticed very brief image drops and loss of sound for a few seconds using a Dreamcast with an ossc going to a dsc 301.

The image drop is extremely short like 1 frame but it takes a couple of seconds to recover sound. It seems to happen irregularly and not very often. I played before for about an hour and noticed no drops but I saw one happen once within 20-30 minutes another time.

It's too fast for me to see if the ossc loses sync and the red light comes on. It has happened often enough for me to notice so I want to fix it.

I didn't play too long with the ossc and gdrom before I installed the gdemu so I can't tell if that has anything to do with it.
Dochartaigh
Posts: 1519
Joined: Thu Mar 02, 2017 6:53 pm

Re: Dreamcast gdemu ossc and dsc 301 brief image drop sound

Post by Dochartaigh »

Guile wrote:I just installed a gdemu and I noticed very brief image drops and loss of sound for a few seconds using a Dreamcast with an ossc going to a dsc 301.

The image drop is extremely short like 1 frame but it takes a couple of seconds to recover sound. It seems to happen irregularly and not very often. I played before for about an hour and noticed no drops but I saw one happen once within 20-30 minutes another time.

It's too fast for me to see if the ossc loses sync and the red light comes on. It has happened often enough for me to notice so I want to fix it.

I didn't play too long with the ossc and gdrom before I installed the gdemu so I can't tell if that has anything to do with it.
Not DC, but OG Xbox of the same/similar era and I have 7 pages in this topic about the DSC 301 HD where I mentioned it several times and nobody seems to have any advice on how to stop the dropouts... Hoping somebody chimes in here with a solution ;)
Guile
Posts: 145
Joined: Sun Jan 03, 2021 10:11 pm

Re: Dreamcast gdemu ossc and dsc 301 brief image drop sound

Post by Guile »

Dochartaigh wrote:
Not DC, but OG Xbox of the same/similar era and I have 7 pages in this topic about the DSC 301 HD where I mentioned it several times and nobody seems to have any advice on how to stop the dropouts... Hoping somebody chimes in here with a solution ;)
I just tried another scaler and I think it probably is the dsc 301 causing the problem but I need to test more. At least I'm relieved if my gdemu is fine. I thought it was glitching when I did the restart to menu button combo but it was actually the dsc 301 not liking the reset. It would go in and out of a blackscreen briefly showing the menu or Dreamcast starting animation.

It's strange I have used the same ossc dsc 301 combo with the og xbox and I don't remember ever having a dropout or audio loss but I haven't really played the Xbox extensively.

It's also strange but on the Dreamcast it does seem to stabilize after the first drop which usually happens within the first 5 minutes. Then I tested for 20-30 minutes with no issues at all.

Ironically trying the other scaler made me realize how much better the dsc 301 looks, extremely sharp and much more colorful at least for Dreamcast. I really would like to solve this, when it's working it's absolute perfection for me for Dreamcast.
Guile
Posts: 145
Joined: Sun Jan 03, 2021 10:11 pm

Re: Dreamcast gdemu ossc and dsc 301 brief image drop sound

Post by Guile »

I've done some more testing and I think I found a solution to the problem at least for Dreamcast. I hooked up the Dreamcast vga out to an rgb interface and then the rgbhv output to the ossc and it seems to have magically eliminated the dsc 301 drops entirely. I tested it for about an hour and even turned the Dreamcast on and off once and I did not see a single drop.

I also tried transcoding vga to component but the drops actually got worse for some reason.

If this helps anyone with the same problem I'd like to know if this is a confirmed fix. I have my og xbox connected by component and don't see drops on the dsc 301 so I can't really test that.

I forgot to mention I also disconnected the AV3 audio from the ossc and ran it to my tv but I doubt that had any effect as it would drop even directly connected to the dsc vga with no sound and no ossc.
Guile
Posts: 145
Joined: Sun Jan 03, 2021 10:11 pm

Post by Guile »

I did some more testing, this time with a GBS-Control. I have some findings that might help someone with similar problems.

Problem 1: GBS-Control Noise (maybe from ground loop)
Fix: Copper tape and component cat5 extender
I had horrible waves of shimmering noise that made the GBS-C unusable unless the source was connected directly to it. I had an idea to use a component cat5 extender to isolate the signal from noise and to my surprise it works extremely well. I can now get a very clean signal from the GBS-Control with no waves or shimmering and a really long distance component signal as a bonus. I also put copper tape on the bottom but the noise was still very bad before using the cat5 extender.

Problem 2: OSSC to DSC 301 Dropouts
Fix: GBS-C and transcoder
The drops would happen on Dreamcast VGA to OSSC to DSC 301 but that was fixed with an rgb interface. I thought it was solved but then I started seeing drops on emulators at 240p from the Wii using component to the OSSC to the DSC 301. Now that the GBS-C noise problem was solved, I thought this could probably help stabilize the signal with the DSC 301.

I haven't tested it long enough but I tried first transcoding the Dreamcast VGA to component, then component to the GBS-C, then to the OSSC and then finally the DSC 301. This resulted in a very nice image and no drops so far. I didn't test the VGA input on the GBS-C because I don't like having to toggle it but it probably would also work. Component out from the Wii to the GBS-C and then the DSC 301 also had no drops so far.
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