BBC Micro Display Settings

[craig_read]

Hi, firstly the information I think you need (excuse me if I make errors but I’m trying to be as accurate as I can, relatively new to this sort of thing)

OSSC v1.7 (I think it is this variant, I am not sure.. the unit is not that old though.. if there is a way I can be certain let me know, but I know it doesn’t have HDR settings)

FW 0.90a

The unit has an HDMI out and I’m using a SCART input to it from a BBC Master computer (UK).

Connecting to an LG 38GL950 monitor, via HDMI.

Initially I couldn’t get anything out of the unit, but after a reset the unit displays the output from the BBC.  The issue I am having is the image isn’t crisp and appears slightly “shimmery” I guess is the best way to describe it.  I’ve been all over stardot forums, trying various settings that others have used.. I’ve tried to understand the wiki for the device but I’m not familiar enough with a lot of the terminology so it’s hard for me to make sense of it.. incidentally often the settings “recommended” from stardot simply result in my monitor displaying nothing and a “No Signal” shown.  Currently the OSSC unit is in a factory reset state, I was wondering if anyone could give me some pointers on where I could start looking to make adjustments.

I apprecaite this is a bit of a noobie question, this is all new to me and a lot of terminology is new.. I just think I am now in a position (after trying for many hours on my own) that I’m better off asking experts.. 🙂

Thanks

Craig

[BuckoA51]

You are probably getting an interlace mode from the BBC Micro? As I remember most games are 240p so the shimmery should go away once you actually start a game.

[craig_read]

To be honest I spend a lot of time on it using command line.. so I was really hoping I could clean up the display.. (I’ve confirmed the OSSC unit is in fact a v1.6).. I was wondering if I could clean up the CLI display…

I am not sure what the BBC is outputing, I think you can change outputs depending on the BBC Mode…

I’ve “copy pasted” something I was following on stardot.. I am hoping this helps;

********************

Firstly set *TV 0,1 – This sets Modes 0-6 to output as 288p instead of 576i. This allows the OSSC to tell the difference between the two video sources.
Go to the output options menu of OSSC, set 240p/288p to Line 2X and 480i/576i to Passthrough. The other options don’t really matter as the beeb won’t generate these modes. This will cause OSSC to output 720x576p50 for modes 0-6 and 720x567i25 for mode 7. These are perfectly standard and very compatible video modes which work fine with both my monitor and my (incredibly finicky) Elgato HD60S capture card.

MODE 0, then in OSSC -> Sampling Options -> Adv Settings:
H. samplerate: 1024
H. synclen: 126
H. backporch: 80
H. active: 720
V. synclen: 2
V. backporch: 15
V. active 288

Exit completely out of the OSSC menu, MODE 7, then OSSC -> Sampling Options -> Adv Settings:
H. samplerate: 1024
H. synclen: 126
H. backporch: 108
H. active: 720
V. synclen: 1
V. backporch: 13
V. active: 288

******************************

If I use this on my device, I get a blank screen and “No Signal”.. I think I can turn interlacing on and off using a command on the BBC… *TV 0,0 turns it on.. I think.. reading that.. I have set *TV 0,1 at the moment.. but I can check that..

• This reply was modified 2 years, 2 months ago by craig_read.

[BuckoA51]

Quite strange that your monitor would not like 576p/50 if it has a HDMI input, did you try line triple instead to see if that is supported? If you just use the default timings, but set the BBC to 288p output, do you get an image on your monitor then?

[craig_read]

I see an image if I reset the OSSC (v1.6 using .90a firmware) to default.. So I’ve set it to default.. the BBC is set to *TV 0,1..  my output is HDMI going to HDMI on the monitor.. model LG 38GL950 (UK).

Please bear with me a bit I’m trying to understand what I do to implement your suggestion..

> Output Opt. > 480i/576i proc .. this it the only line that I can change that makes a difference in the top few lines…

Passthru > I get the shimmery image.

Line 2x > “No Signal”

Line 3x > (Laced) > “No Signal”

Linve 4x (b0b) > “No Signal”

And occasionall “Out of Range” will pop up too..  Again I’m just not sure what any of this means..

I do see an image on the screen.. but the image from the BBC on the screen is very shimmery.. and not clean… so it’s quite uncomfortable to view..   I’ve tried multiple settings and playing around without any luck.. (but I don’t really know what I’m doing.. hence being on here)..

I’ve tried the settings below… as these were recommended on Stardot by others.. Hoping that this would work and improve this..;

MODE 0, then in OSSC -> Sampling Options -> Adv Settings:
H. samplerate: 1024
H. synclen: 126
H. backporch: 80
H. active: 720
V. synclen: 2
V. backporch: 15
V. active 288

Exit completely out of the OSSC menu, MODE 7, then OSSC -> Sampling Options -> Adv Settings:
H. samplerate: 1024
H. synclen: 126
H. backporch: 108
H. active: 720
V. synclen: 1
V. backporch: 13
V. active: 288

For both circumstances.. I get “No Signal”… basically the moment I change the sample rate from 864 to any other value I get a blank screen… I’ve tried setting all values and the picture never comes back till I reset the device to defaults again… I don’t know what settings to change to improve the picture… for what it’s worth.. the OSD menu is crystal clear… Is there anything I can try or is this an incompatibility with my monitor?

 

• This reply was modified 2 years, 2 months ago by craig_read.
• This reply was modified 2 years, 2 months ago by craig_read.

[Zacabeb]

Many monitors and TVs aren’t happy with 50 Hz signals unless they are close to standard video timings. With refresh rates of 56 Hz and up, their acceptance of computer resolutions kicks in making them accept more resolutions including non-standard ones that don’t quite comply with ITU-R, SMPTE, or CVT.

I think Bucko’s suggestion of switching the BBC Micro into non-interlaced mode and sticking with the default OSSC sampling settings is the best solution. An alternative if that doesn’t work is to get a video scaler that can do adaptive de-interlacing to remove the shimmer.

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