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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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JackAsser
Registered: Jun 2002
Posts: 1989 |
Quote: poke53265,0
Dunno if you're were trying to make a joke Oswald.. :D Anyways, that poke doesn't disable the horizontal syncs, hence the high pitched noise will remain. On my C64 where this noise was rather extreme I insulated the h-sync signal and copper taped the whole VIC-cage. This helped very much. IIRC my boss added some sort of filter as well + did something with the line-in on the SID-chip. I'll ask him when he comes back. |
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WVL
Registered: Mar 2002
Posts: 886 |
Quote: is it possible to disable the VIC without MMC64? if so, how to do it?
lda #$0b
sta $d011
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The 'noise' mainly comes from data flowing through the channels. But I'm wondering if this really helps? Isnt the design of the Vic such that it _must_ fetch a byte every cycle? I think the best would be to simply fill up a bank completely with 00's and let the vic display that, aswell as turning the screen off.
Then I'd let the 6502 do as little as possible by only doing lda #$a9 (or similar) when you don't have to jsr to the tune.. |
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Oswald
Registered: Apr 2002
Posts: 5017 |
jack, well if pressing space on the mmc64 equals turning the display enable bit 0, then my answer is correct I guess :) |
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aeeben
Registered: May 2002
Posts: 42 |
lda #$08
sta $d417
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JackAsser
Registered: Jun 2002
Posts: 1989 |
Quote: lda #$08
sta $d417
Ok... what noise are we talking about here? The high-pitched noise or some general white noise?
The high-pitched noise comes from the h-syncs for a fact, about 15625Hz. General white noise I dunno where that comes from.
Poking into $d011 with any value will NEVER change the hsync behavior (unless it's a C128).
@Oswald: Yeah, got your point now.. ;D |
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gregg
Account closed
Registered: Apr 2005
Posts: 56 |
I dunno why, but setting DEN=0 gets rid of a lot of low-pitched noise... they hsync noise doesn't matter much for me. It's probably possible to cutoff at 15Khz without any real side-effects anyway. |
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Devia
Registered: Oct 2004
Posts: 401 |
Actually, disabling DEN and setting $d020 to 0, will reduce the h-sync noise considerably. Setting $d020 and $d021 to 0 and clearing $0400 will do just about the same. The point is that there should be no pixel changes to the display. Adding random noise to the screen increases the noise and it seems the "lighter" the colour of the screen-noise, the louder the audible noise.
It's been a while since I did experiments on this, but please do correct me if I'm remembering something wrong here ;-)
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chancer
Registered: Apr 2003
Posts: 342 |
depends in what sense you mean exactly? to record to audio etc. or just generally.
if its audio as mason said before, you could just run an EQ cut on the sound.. and that will eliminate the frequencies.. e.g. anything under say 30-40hz or the high end.. so it gates the sound.
another way of doing that is running it thru a graphic eq, and boosting / muting certain frequencies.
as for the chips, hhm just before its going to audio.. it's either capacitors or resistors, i forget which, although i'm sure its capacitors.. but put them on the cable OUT of the c64.. again that acts like a gate. that techique i used with car audio, so although the cross over will seperate the signal in frequencies, the mid range, had a capacitor and the rest went to the tweeters.
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MagerValp
Registered: Dec 2001
Posts: 1055 |
Again, grounding the SID input line, preferably via a 100 Ohm resistor or so, makes a the SID a lot less susceptible to picking up noise. A blank, black screen makes the VIC produce less noise. Combine as needed.
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blinkenlichten
Account closed
Registered: Aug 2003
Posts: 4 |
Yes, bad grounding is most likely the reason for your high freq noise. This is from my experience with my record players, but the principle should apply to any audio equipment. |
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