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Forums > C64 Coding > White Screen Bleeding Into Audio
2018-10-08 14:40
Raistlin

Registered: Mar 2007
Posts: 110
White Screen Bleeding Into Audio

This topic has come up a few times now with people I've spoken to ... but Google isn't helping me out here so I just want to make sure that I'm not totally mis-remembering history...

It's my belief that on C64, full-white screens and even screens with large blocks of white should be avoided due to some sort of audio distortion (on a REAL c64).

Was this an actual problem? (I believe it was.. I certainly saw/heard the problem on my C64 back in the day)

Was it particular to certain models of C64?

Was it particular to certain cables? I always used composite or aerial lead...

IIRC, Amiga didn't have this problem at all.



This would then lead into some follow questions... eg:-

- how much white is too much?

- will other bright colours cause this problem? Eg. light green? Off white? Yellow?
 
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2018-10-08 18:34
Oswald

Registered: Apr 2002
Posts: 4291
white screens were generally a big no no on the real thing. you got more noise from tv, and you got your eyes bleed and you couldnt see a thing. led display white is totally different light gray at best.
2018-10-10 00:25
STE'86

Registered: Jul 2009
Posts: 272
ha. yes it was a well known feature of c64s on tvs of the day :)

I always wondered, at one point the crt emu of Vice would buzz like hell and warp the screen slightly when too much white was displayed :)
2018-10-10 00:32
Groepaz

Registered: Dec 2001
Posts: 8842
the buzz is there, enable "video to audio leak" :)
2018-10-10 03:53
STE'86

Registered: Jul 2009
Posts: 272
:D
2018-10-10 13:07
Golara

Registered: Jan 2018
Posts: 87
This is semi related I guess...
My TV (and I tried 2 different CRT TVs) get warped when there's a lot of white on the screen. Not just on C64 but also on Amiga500.
2018-10-10 13:55
Krill

Registered: Apr 2002
Posts: 1063
"On some monitors the image expands in bright areas and contracts in dimmer areas. This happens because the monitor has a poor high-voltage regulation. This effect is more or less visible in all monitors, but normally more so in very cheap monitor models, as it is not inexpensive to design and manufacture a very good high-voltage regulation system. If your monitor has a very bad screen regulation, the picture "zooms" when you adjust the brightness control."
2018-10-11 12:01
enthusi

Registered: May 2004
Posts: 651
There is a full screen upscroller by Graham (Comalight12 or something?) to the music of 'sweet dreams' and it flashes white. That had a very cool zoom effect on my old big TV ;-)
2018-10-11 12:04
Groepaz

Registered: Dec 2001
Posts: 8842
the intro of cucumber juice 2 flashes white for the same reason :)
2018-10-11 16:37
Taskmaster

Registered: Feb 2018
Posts: 2
Bizarrely, I actually remember that. I would avoid using a white border in my programs because I hated the way the screen would distort.

Funny the things you'll just accept when you're young and not question... Nowadays, I'd devote at least 2 hours into internet sleuthing trying to figure out why it's doing that and how to stop it.
2018-10-12 08:56
Grue

Registered: Dec 2001
Posts: 100
Audio bleeding also happens inside c64 voltage rails. SID-chip spec sheet states that separate voltage and gnd-lines should be used but Commodore shared them with VIC-II. This results very noisy +12v and +5v voltage lines to SID.

This is easily heard if you do in basic:

poke 53280,1:poke 53281,0

and turn up the volume. You can shut down display if you use line-out for audio to hear this same :)

It seems that in 8580's there's better insulation what comes into noisy voltages bleeding into audio output, but it can be heard there too, but not as loud as on 6581's
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