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Raistlin
Registered: Mar 2007
Posts: 680 |
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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JackAsser
Registered: Jun 2002
Posts: 2014 |
Exploited by Vicious Sid and emulated by VICE |
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chatGPZ
Registered: Dec 2001
Posts: 11386 |
there are two things that happen:
a) crosstalk between audio and video. this happens inside the C64, in the cables, in the monitor... and it may vary wildly between individual setups. this results in part of the videosignal ending up in the audio signal, which then results in typical buzz
b) electromagnetic interference. this happens in the monitor. since there is a rather strong magnetic field around the tube, it interacts with the audio amplifier circuits in a way that you can then hear it. in this case you can even disconnect the audio-input from the monitor, you will still get this side effect (eg with my 1701 i can still hear the vicious sid sample when i do this)
[c) crosstalk due to RF encoding of the signal. lets ignore this =P]
the problem exists with all colors, and will get worse the higher the contrast against black is. that is because in every line there is first black level, then the picture.
i wouldnt worry too much though :) |
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Raistlin
Registered: Mar 2007
Posts: 680 |
So... the concensus in the 21st century is that this isn’t a problem any more..? As in, demos and games can happily use all the colours without worrying about audio and video banding? |
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chatGPZ
Registered: Dec 2001
Posts: 11386 |
not sure if that was ever a problem at all =P |
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Raistlin
Registered: Mar 2007
Posts: 680 |
Oh. I must've had a cheap TV back in the 80s then ... I'll blame my parents. |
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chatGPZ
Registered: Dec 2001
Posts: 11386 |
what i ment is: noone considered it a real problem. just turn up the volume. or something :) |
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Oswald
Registered: Apr 2002
Posts: 5094 |
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. |
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STE'86
Registered: Jul 2009
Posts: 274 |
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 :) |
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chatGPZ
Registered: Dec 2001
Posts: 11386 |
the buzz is there, enable "video to audio leak" :) |
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STE'86
Registered: Jul 2009
Posts: 274 |
:D |
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Golara
Account closed
Registered: Jan 2018
Posts: 212 |
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. |
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Krill
Registered: Apr 2002
Posts: 2980 |
"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." |
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enthusi
Registered: May 2004
Posts: 677 |
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 ;-) |
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chatGPZ
Registered: Dec 2001
Posts: 11386 |
the intro of cucumber juice 2 flashes white for the same reason :) |
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Taskmaster
Account closed
Registered: Feb 2018
Posts: 22 |
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. |
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Grue
Registered: Dec 2001
Posts: 162 |
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 |
