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Old 13 August 2016, 23:08   #1
Mrs Beanbag
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Eek A 5th Audio Channel on the Amiga

ok so someone plugged his Amiga's composite out signal into an amp and played samples over it by drawing on the screen

http://jmp.no/blog/a-5th-audio-channel-on-the-amiga
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Old 13 August 2016, 23:47   #2
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Yeah nice, this is possible with any machine that outputs composite.
Here's a C64 demo that did this a long while ago using VIC noise:

[ Show youtube player ]
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Old 14 August 2016, 12:04   #3
Retro1234
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Can you have anything on screen but static?
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Old 15 August 2016, 00:20   #4
Mrs Beanbag
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if you were clever perhaps you could put something else on the screen, maybe using colour, i don't know... the C64 video posted above also has a scroller across the middle. The problem is it's the pattern on the screen that produces the sound. Then again if you were using something like Indivision or the HDMI output of the Vampire accelerator you could still output this stuff to composite while displaying something else independently on the other output (?)
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Old 15 August 2016, 01:19   #5
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Maybe you can have something on both RTG and normal display?
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Old 15 August 2016, 18:34   #6
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I thought you couldn't have RTG and standard display at once.
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Old 15 August 2016, 19:46   #7
Thorham
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Interesting hack. Too bad it's not useful.
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Old 16 August 2016, 10:58   #8
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The OS doesn't support using both at once, but there's no technical reason I can think of that you can't bang the hardware directly to get output on the native screen.
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Old 16 August 2016, 19:53   #9
pandy71
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Quote:
Originally Posted by Mrs Beanbag View Post
ok so someone plugged his Amiga's composite out signal into an amp and played samples over it by drawing on the screen

http://jmp.no/blog/a-5th-audio-channel-on-the-amiga

I have better hack for you - use 4 bit TTL output from video port in same way as DCTV or HAM-E or similar.
Code PCM on video then collect data - you can realtively easy output 16 bit stereo PCM 48kHz even on naked A500 in such way - this can be done with simple state machine on few TTL circuits, on hires line (640 pixels) 320 bytes can be coded so single line can cary 16000 bytes per second to feed 48000 16 bit stereo you need 12 hires lines - this area can be masked in TTL logic to avoid visible garbage...
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Old 18 August 2016, 00:15   #10
Mrs Beanbag
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i did wonder today about using sprites instead of copper palette changes to achieve the effect. so one could render samples into sprites and play with 8 channels by putting the sprites in different places! (Maybe repeating them across the screen to increase the loudness)
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