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How to get the pixel/dot clock of an arcade game for the OSSC

Paranoid_Andy

Paranoid_Andy

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Hey everyone,

I'm wanting to use the OSSC with my supergun and I could use some help dialing the picture in properly. I don't know how to get the proper sample rate though.

Do anybody know how to get the sample rate of an arcade PCB?

If you do, could you please include a detailed example please so I can understand the math behind it.

Thank you for any help!

***UPDATE***
I have all the info to calculate the sample rate except the pixel/dot clock rate. I just need to find out how to get that value from a PCB.
 
Last edited:
I'm not sure I know how to answer this, but what PCB are you trying to do this with?
 
I thought an ossc auto detected the proper rate?

What supergun and board are you using?
Are you using video out of the supergun(if applicable)?
 
@XtraSmiley These are what I will currently be trying to setup.
Aliens
CPS1 Multi
CPS2 Multi
Demon Front
Denjin Makai 2
E.D.F.
Final Fight
Growl
Neo Geo Multi
The Outfoxies
PGM
Sega ST-V Multi
Taito F3 Multi
TMNT
Boogie Wings
The Combatribes
Hellfire
Ninja Baseball Bat Man
Shadow Force
Thunder Hoop
Thunder Hoop 2
Twin Eagle
Irem M72 Multi
Zero Team

@PlatynumX I'm using this supergun: https://8bitplus.co.uk/articles/progamer-supergun-retroelectronik-review/
The video out is via scart cable.

I've never seen sample rate ever auto detected by the OSSC. It has pre-configured settings to make a best guess but anything out of the mainstream consoles needs an exact sample rate from what I've learned.
 
(...other than hooking the pcb up to an oscilloscope) When you boot a rom in mame, it will display the video resolution. Some games are not timed perfectly, but they will tell you that in the warning screen. I don’t use an ossc much though so I don’t know how to make use of that info.

Neo Geo for example:

1694127581727.png
 
Marvelous collection! Lucky for you I have all of those PCBs and all have worked with the OSSC for me (except my Zero Team which has weird sync issues).

That being said, when you plug it into the OSSC it shows data about the game on the OSSC screen and I believe it's the same that is in that MAME window above. I'm not sure what you're trying to dial in exactly. I use the "Generic 5x" settings and everything looks sharp and works well. If the game has info cut off due to 5x (some top and bottom will be cut), I switch to 3x.

By the way, a long time ago that particular SuperGun had issues with voltages that could damage PCBs, so if you have a way to check that, I would before using some of your more expensive boards... BoogieWings... :P

EDIT: Oh and depending on which OSSC rev you have F3 might cause you issues, but if you feed it through AV3 it should work.
 
@ekorz
That might be helpful... still trying to piece things together.

I found this post that explains how to calculate sample rate of a console: https://videogameperfection.com/forums/topic/calculating-h-samplerate/

Pixel clock / horizontal freq = sample rate
Horizontal freq = vertical refresh x scanlines

You can read both horiz freq, vert freq and line count from OSSC info window.

Example of SNES formula:
Horizontal Freq of 60Hz x 262(total scanlines) = 15720

SNES runs at 5.37MHz or 5370000Hz

5370000 / 15720 = Sample rate of 341

This is very helpful but I think I'm missing 1 key piece of information. The pixel clock.

I guess my next question should be, does anybody know how to identify the pixel clock of an arcade game? Maybe the screenshot you linked Ekorz numbers is the pixel clock?
 
Totally off topic question, is your NBBM a US version? If so, can you post a pic of the silver label and the serial number? If not US version, don't sweat it.
 
The pixel clock refresh rate is displayed on the OSSC screen (same as in MAME I think). I'm still not sure I understand what you're trying to do with the information though.

Here are the advance settings info, I'm not knowledgeable enough to answer you question though:

https://junkerhq.net/xrgb/index.php?title=OSSC#Advanced_timing_tweaker

You may want to post here instead. The OSSC creator Marqs is pretty good about jumping in and answering questions:

https://shmups.system11.org/viewtopic.php?t=52158
 
Last edited:
@XtraSmiley Thanks for the heads up on the supergun. I've had it for a few years now and actually used all the PCBs on it many times before without issue so I think it's okay. Probably a newer model I'd think.

I used to use Generic X settings too but once I saw what happens when you dial the settings in exactly.. well it just looks too good and I'm wanting to make all my games look that good lol.

Odd you couldn't get Zero Team to work. Mine worked fine on 4x IIRC.

I can't recall what region my NBBM is but can update here next time I plug it in.

I didn't realize the pixel clock is on the OSSC screen. I'll have to check that right now. Perhaps everything I need is there then and I just have to crunch the numbers. I'll report back.
 
Okay I think terminology confused me a little bit but it seems the OSSC is providing me with everything I need except the Dot Clock which is also called Pixel Clock it seems.

So the SNES has a dot/pixel clock of 5.37MHz. So if I can figure out what the clock of a PCB is, then I'm good to go. I'm just not sure how to get that number or if any of the numbers Ekorz showed would be what I need. I report any further findings.
 
Paranoid_Andy said:
Hey everyone,

I'm wanting to use the OSSC with my supergun and I could use some help dialing the picture in properly. I don't know how to get the proper sample rate though.

Do anybody know how to get the sample rate of an arcade PCB?

If you do, could you please include a detailed example please so I can understand the math behind it.

Thank you for any help!

***UPDATE***
I have all the info to calculate the sample rate except the pixel/dot clock rate. I just need to find out how to get that value from a PCB.
Click to expand...
Short answer - you can't. You need the total number of "pixels" pr line, which would include the sync pulses, the black borders on each side etc.
 
ImportantBet said:
That's the refresh rate. So you've been confusing OP the entire time lol.

Pixel clock is entirely different. For instance, CPS1/2 would be 8 MHz.
Click to expand...
Well, I hope I wasn't confusing him, but I did say I didn't know! That number (refresh rate) is also what MAME provides, so I don't think he's going to get what he wants there either.

Also, since you know it for CPS 1/2, can you explain how you know and potentially help him out?
 
How did you know the CPS 1/2 pixel clock? Was it available on the Internet, did you analyze the PCB, or was it in the MAME data?
 
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