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Filtering PC "processor" noise through speakers
Filtering PC "processor" noise through speakers
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Old 28th September 2017, 11:43 AM   #1
italie is offline italie
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Default Filtering PC "processor" noise through speakers

Looking for tips in tracing down and eliminating "Processor" noise coming through the speakers. A bit hard to explain, but it's the high pitched "modem-like" noises when GFX are in motion on a screen or the processor is busy.

I've heard old remedies like turning off inputs and BOIS tweaks, but I'm not hearing much on what actually causes it on any given motherboard. Is it often the audio chip? Bleed on the 12V from the video line?

Putting a scope on it this afternoon, but wanted to gather advice.


Thanks.
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Old 28th September 2017, 12:29 PM   #2
abraxalito is offline abraxalito  United Kingdom
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Ground noise is the usual culprit - you'll probably gain some relief through isolating the computer audio output via transformers. No need to shell out on 'audiophile' grade ones, cheap iron core ones do the trick. This kind of thing - 10K:10K Z11矽钢片音频隔离变压器 平衡和非平衡转换 音频隔离器-淘宝网全球站
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Old 28th September 2017, 12:33 PM   #3
Kjeldsen is offline Kjeldsen  Denmark
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I also experience this, with and external soundcard via USB. I guess USB by natur is isolated?
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Old 28th September 2017, 12:47 PM   #4
abraxalito is offline abraxalito  United Kingdom
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No, USB isn't isolated by nature. If you're not going beyond 96kHz sample rate, the isolation can be incorporated fairly cheaply as there are single chip solutions (e.g. Analog Devices). For higher rates there is one single chip solution available (Silanna) but its fairly pricey.
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Old 28th September 2017, 01:13 PM   #5
djoffe is offline djoffe  United States
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I agree...ground noise is the usual culprit. As an experiment, simplify the system as much as possible...just the PC and the amp...then, as an experiment, use a ground lifter to disconnect GWG (green wire ground) from the amp. Doing so will usually quiet things down a lot. Important: As to lifted GWG/safety, some folks would complain.

However, if it fixes your problem, you could build a ground lifter that maintains the safety connection while improving the audio noise situation.
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Old 28th September 2017, 02:42 PM   #6
italie is offline italie
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Tried a standard ground loop isolator, it lessens the noise, but doesn't eliminate it. Digging in further in a few hours.
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Old 29th September 2017, 02:42 AM   #7
dangus is offline dangus  Canada
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Filtering PC "processor" noise through speakers
About the best you can do is turn the volume up on the computer and reduce it as necessary on the powered speakers or headphones. That maximizes the signal to noise ratio. I assume it's caused by a failure to provide the DAC chip with clean power.

The best is to use an internal or external sound card or device. Decent PCI cards are dirt cheap at computer recyclers. At least, if your computer still has a PCI slot... Or if it has s/pdif output, use an outboard DAC or AV receiver.

Last edited by dangus; 29th September 2017 at 02:47 AM.
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Old 29th September 2017, 06:08 AM   #8
xx3stksm is offline xx3stksm  Japan
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There are many posts about "modem-like" noise " on youtube. It usually comes from ground loop and USB. An isolating transformer for ground loop and USB isolator for USB are usually effective. Many countries use three terminals power; two is for power, one is for earth ground. Earth ground is for safety. That's why a ground lifter is not recommended. But some countries use two terminals power e.g.japan. I don't know many people get an electric shock in Japan. I have doubts about that, IMHO.
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Old 29th September 2017, 07:48 AM   #9
Kjeldsen is offline Kjeldsen  Denmark
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With two terminals only it's important that the electronic devices are designet for this (dual insulation). It might be illegal in your country to connect a three terminal device in a two pin socket.
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Old 29th September 2017, 11:00 PM   #10
dangus is offline dangus  Canada
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Filtering PC "processor" noise through speakers
I think the problem is digital engineers who don't know that codecs require clean regulated power to achieve the performance numbers on the data sheet. If you're lucky, they'll copy the reference design, and then the numbers they've copied off the data sheet will actually be real.
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