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Dr. 8 Bit
Account closed
Registered: Sep 2006
Posts: 25 |
reduce the audio-noise
How can I reduce the audio-noise from c64?? some ideas?? a capcitor...mmm.. |
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MagerValp
Registered: Dec 2001
Posts: 1055 |
On your average C64 the SID input is unconnected and floating, and basically acting as an antenna. Not good.
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chatGPZ
Registered: Dec 2001
Posts: 11107 |
depending where you live, you can stick a capacitor in there and listen to AM radio =) |
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uneksija
Registered: Jan 2002
Posts: 44 |
I've tried the "ground the input"-trick. I didn't use any resistor, I simply used a shorted plug (so basically, I wasn't even hacking the hardware). The results were amazing. Almost all of the noise disappeared. No need for any other tricks... |
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gregg
Account closed
Registered: Apr 2005
Posts: 56 |
As long as you don't short-cut the internal capacitor that is in the audio-in line, it should be safe.
I simply soldered both pins in the DIN-plug together, they are right next to each other.
So, put audio-in to ground, lda #0 sta $d011 sta $d020 and no noise whatsoever anymore for me. :) |
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Hate Bush
Registered: Jul 2002
Posts: 453 |
uneksija, gregg: how to _exactly_ modify the plug? care to tell me in details? sadly, i'm an idiot when it comes to any modding. |
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dalezy
Registered: Apr 2002
Posts: 475 |
has anyone ever tried to plug a separator filter between the c64 and the recording target? i used such a thing before to filter out the noise in my amp that was caused by my screen, time to search for that cable and try it out =) |
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Devia
Registered: Oct 2004
Posts: 401 |
Randall: Just open up the DIN plug and short the two pins labeled 2 and 5
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Frantic
Registered: Mar 2003
Posts: 1627 |
I guess this is in accordance (somehow?) with what me and Twoflower found while doing some sid tests once. We found that reading voice 3 when playing combined waveform 5 had slightly different results on different 8580-machines. Some produced more high values (above $80) than others. We didn't do it very carefully (i.e. "sampling" each cycle with a REU) but bascially just did some non timed polling, but the results were consistent at least. Machines known as "skärmtjutare" in swedish (made in Hong Kong or something?) = machines that produce a lot of audio noise (a "hissing noise") when the screen is bright, also produced more "high values" in voice three. I guess it was basically some kind of noise, rather than the waveform actually being different in these chips.
We dealed with this when investigating SID chip detection, but since then I learned better ways of detecting the sid anyway, and never cared much about checking it further.
However, I guess someone might have some ideas about this. I suck at hardware, so I don't really have any theories.
Perhaps this "feature" can be used to detect wheter a digital android is using the machine (i.e. Iopop and others'), rather than a analogue human (which wouldn't cause any interrrferrrence with the digital equipment)? ;) |
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uneksija
Registered: Jan 2002
Posts: 44 |
...Or do it like me: I've got an adapter cable that has the DIN plug on the other end and four female RCA's on the other end. One of the RCA's is the audio output and one is the audio input. I made a special plug for grounding the audio input. The plug is simply a male RCA plug, which I had shorted by soldering a little wire (a piece of a component leg actually) between the signal and ground of the plug. I'd send a picture which would really give you the idea, but I don't have my plug here at the moment. This special plug I insert to the audio input (while C64 is turned OFF!) and ta dah! Noise is gone! I've heard this might also boost digis on an 8580 (don't know if it's true), but I haven't tried it, because my old C64C has probelms with its TV-signal (Will fix this soon). |
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ready.
Registered: Feb 2003
Posts: 441 |
No, this will not boost any digis on 8580 model. In fact the right way to implement this is to ground the actual SID pin via a resistor to ground. Remeber that between AUDIO IN pin on SID and AUDIO IN on connector on the rear side of the C64c, there is a capacitor to ground.
You have to put the resistor between sid pin and capacitor, otherwise you will not get $d814-digi replay.
Anyways this modification has to be done on the C64 board (I actually soldered on the 8580 pin) and it works great. Except you loose the feature that 8580 does not produce click when changing the volume $d814.
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