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Digital Audio, The Cure for Noise?

Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=52972
Printed Date: October 31, 2024 at 5:51 PM


Topic: Digital Audio, The Cure for Noise?

Posted By: SiDogg
Subject: Digital Audio, The Cure for Noise?
Date Posted: March 31, 2005 at 11:20 PM

Forget about WHERE a noise is coming from for a moment, let's say it is there and there is nothing you can do about it.

How do you get rid of it?

Can you get rid of it by reading digital music, such as MP3s or a CD, into a device which has digital output (S/PDIF), to a Digital DSP (5.1 decoder) to the amplifier via RCA cables?

Does this make sense? Noise comes from an echo or extra voltage on the wire, right? So if the source is clean and the device reading the source reads digital format and does no ADC conversion, and outputs digitally to a non-noise-infected source, such as a high-end digital DSP, then there is no way for noise to get into the system, right??



Replies:

Posted By: deocder
Date Posted: April 01, 2005 at 2:05 AM
Damn dude! You think to much!

Actually you got me thinking....

Lets try to figure this out.....

Crap, I cant do it.....too tired..posted_image

But I am curious...

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Posted By: kfr01
Date Posted: April 01, 2005 at 2:54 AM
A coax digital connection will still carry current. Ground loops are still possible. Noise can enter the system this way. An optical digital connection would not have this problem. However, neither are always perfect because of jitter issues.

At some point a DA conversion must be made. Unless this conversion is done in the amplifier itself, there will be interconnects carrying an analog signal.

But yes, other people have thought of this too. Check out this Optical Digital Reference line by Pioneer UK: https://www.pioneer.co.uk/files/brochures/04_CE_ODR/04_CE_ODR_EN.pdf

McIntosh Labs also sells an outboard car audio DAC.

To me this sort of upgrade should be far down the list of priorities if you're operating on a budget. It should be a choice made to improve sound quality - not as the most expensive noise band-aid known to man. :-)

If you convince yourself you need something like this I'd first suggest making your front stage near perfect so you'll actually be able to appreciate the sonic upgrade.

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New Project: 2003 Pathfinder




Posted By: DYohn
Date Posted: April 01, 2005 at 9:16 AM

The answer to your question is yes and no.  Yes, it is possible for a DSP to remove specific types of noise from the signal path.  It can just as easily introduce other types of noise (like digital artifacts.)  And No, audio that you can hear has to be analog (speakers and the amplifier that drives them.)  The power from your vehicle's alternator (or your home power system) is analog and seperate from the signal path.  So any noise being introduced after the DSP (in the amp or the speakers) or that is not affected by the DSP (in the power chain) cannot be controled by this sort of digital signal manipulation.

Digital is a great way to easily manipulate and transport audio files, and it can achieve excellent sound quality more cheaply than can analog equipment.  But it is not a cure for all ills.



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Posted By: SiDogg
Date Posted: April 01, 2005 at 10:33 AM
Right, I understand that any noise interference in my amp or the piece doing the DA conversion (the DSP itself) is still susceptible to noise. But most car audio devices are built in a way to avoid noise.

The source here, if you are wondering, is a computer playing DVD and MP3 files.

It is probably a great home to noise; however, I can avoid all noise if I unplug the LCD (VGA port). So the LCD is allowing noise to go through it, into the VGA port on the motherboard, and thus resonating out into the RCA cables to the amp. I figure inserting optical and digital DSP between the motherboard and amp, I will no longer have this noise issue, since it cannot resonate into the amp any longer. And the PC should not have noisy digital music, because it wouldn't be doing any ADC conversion since the DVD (IDE) and MP3 (binary data) are all digitally accessed.

Or am I on crack?   :)






Posted By: DYohn
Date Posted: April 01, 2005 at 10:44 AM

OK, so now we move from theory to application.  You're telling me you have a computer music source and a noise problem.  Is this in your car or in your home?  What kind of noise are you hearing?

The two most likely culprits are your sound card and the system ground plane.  What sound card are you using?  How is the system grounded?

And by the way, a DSP (digital signal processor) is not the device that provides the digital to analog conversion.  That is the DAC (digital-analog converter) and in a computer is your sound card.



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Posted By: Drewt
Date Posted: April 01, 2005 at 11:50 AM
what you can do is get a card that will give you an optical output from your computer, then take that to a flying cow DAC in the back, and have your amp pretty close to that. The noise verry well may be comming from the other stuff in the computer, interacting with the sound card.

-Drew

Edit: for the very best sound quality, you'd want analog throught, no digital whatsoever. But, since the audio industry has made us think that CD quality is "perfect", no one else knows that....

It would be slick if you could get an amp like the Alpine MRD-M501, and pull out the ADC in that, and push the digital signal straight to the DSP...

-Drew

-Drew




Posted By: SiDogg
Date Posted: April 01, 2005 at 7:28 PM
DYohn: It is not my PC. You are not listening to me. If I unplug the LCD VGA cable to the PC, the noise is gone. Maybe because my PC is not grounded, I am letting the noise go through to the RCA cables, but it is not my PC making the noise. The noise is about 200Hz and it is a buzz like "line noise". It is not "white noise" though. The amp can filter it out, but it's too high for me to keep the filter on as it kills my mids.

By the way, I did try another sound card -- one certified with THX and is 7.1 capable and has an HD codec of some sort as well. It is the Audigy 2ZS from Creative. But it installs by screwing into the PC case, because it's a PCI card, and it made the sound even worse, by making the noise come from the PC case as well as from the LCD VGA cable. I tried grounding the case all over and even extra grounds for the motherboard. No luck.

Only ground thing I haven't changed yet is the ground distro block in my trunk... *sigh* Maybe I will just to see if that helps.

Drew: That is what I'm planning on doing. My motherboard has native S/PDIF out. :)




Posted By: DYohn
Date Posted: April 01, 2005 at 8:12 PM

What you are describing are textbook symptoms of a ground loop probably caused by trying to integrate a PC into an automobile.  What are you using for a power supply?



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Posted By: customsuburb
Date Posted: April 01, 2005 at 8:16 PM

Drewt] wrote:

br>
...It would be slick if you could get an amp like the Alpine MRD-M501, and pull out the ADC in that, and push the digital signal straight to the DSP...

-Drew

-Drew

Whoa, this Alpine amp has two optical inputs and what looks like a built in dobly digital and DTS processor... https://iweb.alpine-usa.com/pls/admn/item_info?p_item_name=MRA-D550&p_category=40&p_subcategory=130&p_main=10 That would be cool if you ran the optical output from your soundcard to the input on that.



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Posted By: SiDogg
Date Posted: April 01, 2005 at 9:01 PM
The carputer has 12v input. It is a DC-DC power supply.




Posted By: Drewt
Date Posted: April 02, 2005 at 12:20 AM
check and see the difference (voltage) and resistance between the ground from the computer PS and the ground on your car...




Posted By: SiDogg
Date Posted: April 02, 2005 at 9:51 AM
you mean measure resitance between battery and car chassis and then between battery and PC ground?




Posted By: haemphyst
Date Posted: April 02, 2005 at 9:56 AM
DYohn hit it on the head. You have a classic ground-loop situation. The only way you can get rid of it is to use all digital, as you have suggested, or a ground loop isolator. The way you are describing your situation, and plaese correct me if I am wrong, is that there is no noise when your LCD is not plugged in. Is this right? When you plug it in, the noise returns? If this is the case, neither of the above solutions will be solutions in your case. Where is your monitor? Is it in the front of the car, and the PC in the back? Are they powered from the same place? If the power for one is coming from a distro in the back, and the power for the other is coming from the fuse block in the front, and they are not using the same point of ground, THIS is where your ground loop is happening. It will be extra work, but run power and ground for both devices to the same point in the car. See if this helps. The ground loop is not CAUSING the noise, the noise is an EFFECT OF the groung loop. By introducing noise to the ground plane of the PC, the soundcard is amplifying the noise present. It, in and of itself, is probably NOT CAUSING the noise. Are your PC outputs short, and connected directly to the amp in the back, and you are using your media player and/or Windows volume control in the PC to control the volume of your music? If this answer is yes, I will assume that your PC is, in fact, NOT causing the noise, but amplifying noise already there...

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."




Posted By: SiDogg
Date Posted: April 02, 2005 at 9:44 PM
Fair enough haemphyst, I do tend to agree, I am just at my whit's end with this.. :( I have literally spent the last 6 months trying to fix it. I keep thinking I make breakthroughs, then nothing. Let me share some additional (gory) details of the wiring:

It all starts at the front. Plugged into the battery I have a 4awg wire. That goes to the trunk to a "platinum" distro block (I wonder how good these really are or if they're just hype btw). The distro block powers EVERYTHING now.. This includes the AMP and an ITPS device. The ITPS is design to regulate voltage to <~12vdc and also provide a startup/shutdown signal to the motherboard to boot the car and give the pc 45 seconds to cleanly shutdown after the car is shut-off. I've tried w/out this device, no luck, so I doubt it is this device.

Off the ITPS I have the LCD and the PC. The PC has native 12vdc input as does the LCD. I used to have the LCD wired to the cigarette lighter (came with the plug) but it didn't make a difference.

The LCD has a VGA cable going to the back to the carputer for video. I have also added a 12v noise filter from radio shack. This didn't help a bit and actually buzzed itself for the first few minutes. I grounded it to the chassis and powered it from the ITPS for the LCD. The LCD still works by getting it's filtered power, but I don't think it made a bit of difference on my system.

The PC is grounded to a gnd distro block (same type) and that to the sanded part of the chassis. I've tried adding extra wires straight from the amp, computer, lcd, itps, and distro block, to increase the quality of the ground -- again, no dice.

The PC had a PC sound card which outputted using 1/8" stereo jacks. I got 1/8" to dual RCA jacks and put my high-quality RCA cables inline (I tried cheapies too btw). These go to my amp. When they are unplugged from the computer, my amp is dead quiet (duh). I never did do the muting plug test.

Even if the PC is off, the noise persists. I removed the sound card and it stopped! I was thrilled. That means the sound resonated from the case, since the PCI card is grounded to the case, the motherboard is not.

Then I plugged my LCD VGA back in -- doh, noise is still there.

So now I realize I need to separate VGA and motherboard, but that is near impossible. Maybe I need to ground my VGA? Will that screw up my video card though? Hmmmm.

Oh, I've even unplugged all of the wiring in my computer, even the power supply itself one time.. Still I get the noise, so it IS coming into the VGA cable.. I also tested the usb and keyboard cables.. Nope, it's DEFINITELY coming in from the VGA cable..

So that points to the LCD.. So maybe it needs to be grounded to the ground distro block or the ITPS?

Hmmmmm... maybe this is my problem... what do you think?


Hmmm, writing this out in the last 10 minutes really has helped me put things in perspective. I bet it's that friggin LCD ground point!! GRRRR!!   *take screwdriver to LCD*

I'll post more after I move the LCD ground....





Posted By: kfr01
Date Posted: April 02, 2005 at 11:45 PM
Yes. You have it. Move the LCD ground to the same point as the others. You need to eliminate differing ground points.

https://www.epanorama.net/documents/groundloop/basics.html

Here's an explanation of your problem.

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Posted By: SiDogg
Date Posted: April 03, 2005 at 5:28 PM
Aaargh.. OK, so I tried grounding the LCD to the amp ground point, and to the computer ground point and to the chassis. No dice! :(

Then, I unplugged the LCD power. It was still buzzing.. That was odd, I thought, so I looked and only the VGA cable was plugged in. So I unplugged that, and the noise was still there. My PC was the only thing plugged in. So I unplugged that and it went away. Same if I would have unplugged the RCA cables.

So I have one ground consolitation cluster and then those ground to the same place the amp is grounded to. So they're all really grounded to the same place.

*sigh*

Anyone in NOR*CAL feel like helping me troubleshoot? :)
FREE BEER!! :D :D





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