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line noise in the system, After 5 years, ready to go...problem.
w1L50n23
post Sep 26 2013, 02:57
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For over 5 years I've been waiting for time to commit my vinyl to pc...now I'm ready to go and there seems to be a problem already.
I have an EMU 1820 sound card and dock. I bought this a long time ago specifically because it had phono ports on the dock. I have an old school Marantz with RCA jacks (not USB) that will jack into the dock.
Now, when I went to do my first test recording, I noticed some line noise bouncing the meters on the virtual soundboard (with no turntable connected yet).
Here is what I have done to track down the problem:
I took the whole computer and turntable down to my shop. This shop is on a totally separate transformer from my house...so this is like taking to to another guy's house. I set it up, and grounded the computer chassis and dock (it has a grounding screw) to a dedicated ground rod I had existing just outside the shop. I shut off all the breakers except the one that powered the computer. No change. I plugged in the turn table and grounded it...same. I put in my headphones and cranked them to max and can hear a hiss, then I shut off the monitor....no change. I have done everything possible to eliminate any external source of interference...so this must be internal to the pc; or maybe a problem with the card/dock?.
What 'this' is, is the meters on the phono strip of the virtual sound board show a signal, on both channels, that don't move together, bouncing from about -47 to -42 (db?) all the time....it doesn't change. As I said, at max. volume on headphones there is a sort of hissing or some sort of sound at least....sort of white noise-ish.

Now my question is...is this 'normal' for pc audio stuff?? Is there always some signal that is inherently there? and...what else can I do to minimize it?
I didn't pay close attention at the house, but it seemed a bit less at the shop with the grounding and isolating and all.
Thanks in advance for advice. I'd like to get going on this...ahem....5 year waiting project.
Wilsen
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Arnold B. Kruege...
post Sep 26 2013, 03:54
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QUOTE (w1L50n23 @ Sep 25 2013, 21:57) *
Now my question is...is this 'normal' for pc audio stuff?? Is there always some signal that is inherently there? and...what else can I do to minimize it?
I didn't pay close attention at the house, but it seemed a bit less at the shop with the grounding and isolating and all.
Thanks in advance for advice. I'd like to get going on this...ahem....5 year waiting project.
Wilsen


You seem confused. PC's aren't inherently noisy, but some of the stuff we attach to them is prone to grounding problems and noise. Case in point would be analog playback devices.

Basic trouble isolation procedures include building the simplest possible system, checking it out, and adding more components one at a time to determine where the noise is coming from.
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cliveb
post Sep 26 2013, 08:15
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QUOTE (w1L50n23 @ Sep 26 2013, 02:57) *
What 'this' is, is the meters on the phono strip of the virtual sound board show a signal, on both channels, that don't move together, bouncing from about -47 to -42 (db?) all the time....it doesn't change. As I said, at max. volume on headphones there is a sort of hissing or some sort of sound at least....sort of white noise-ish.

I'm not familiar with the EMU 1820, but a quick google indicates it has a built-in phono preamp. Assuming this is the input you've selected, then it could simply be that the phono preamp on the 1820 is noisy. (-47 to -42dB is pretty poor, but believable - especially if that's a peak rather than RMS level).

One thing you could try would be to select the line input instead of the phono on the 1820 and see what noise levels you get then. If the noise drops dramatically, that's a good indication the problem is in the 1820's phono preamp. If that turns out to be the problem, and if you feel the noise level is too high, then the obvious solution is to get a dedicated phono preamp and feed it into the 1820's line input.
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Juha
post Sep 26 2013, 08:39
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Are you sure it's not low hum there on background? Try if shielding the turntable into GND of RCA socket instead of 1820 GND helps anything.

Thouhg, once I had this similar hissing problem w/ Creative soundcard on a turntable setup. Noise was related to some other available input ports which were left fully open (MME/DS/WDM picked that port). Closing the ports helped but as well, problem become fixed by using ASIO.

Juha

This post has been edited by Juha: Sep 26 2013, 09:01
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2Bdecided
post Sep 26 2013, 09:17
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Connect the turntable, play some vinyl, and see/hear how the background noise you're currently worrying about compares with the background noise of vinyl. Then decide whether you need to do anything.

While you should do the best you can anyway, when everything is connected and the levels are set correctly, you might not be able to detect this noise due to some other noise!

Cheers,
David.
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Juha
post Sep 26 2013, 10:03
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QUOTE (2Bdecided @ Sep 26 2013, 11:17) *
Connect the turntable, play some vinyl, and see/hear how the background noise you're currently worrying about compares with the background noise of vinyl. Then decide whether you need to do anything.

While you should do the best you can anyway, when everything is connected and the levels are set correctly, you might not be able to detect this noise due to some other noise!

Cheers,
David.


Rumble and some other low frequency noises (of vinyl and setup related noises) can be removed afterwards by using a steep enough HP filter (try 36dB-48dB/oct @30Hz-50Hz).

Juha

This post has been edited by Juha: Sep 26 2013, 10:07
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Arnold B. Kruege...
post Sep 26 2013, 12:41
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QUOTE (Juha @ Sep 26 2013, 05:03) *
QUOTE (2Bdecided @ Sep 26 2013, 11:17) *
Connect the turntable, play some vinyl, and see/hear how the background noise you're currently worrying about compares with the background noise of vinyl. Then decide whether you need to do anything.

While you should do the best you can anyway, when everything is connected and the levels are set correctly, you might not be able to detect this noise due to some other noise!


Rumble and some other low frequency noises (of vinyl and setup related noises) can be removed afterwards by using a steep enough HP filter (try 36dB-48dB/oct @30Hz-50Hz).



Agreed. The problem is to remove the noise without removing the music, and also without creating a noise floor that has detrimental audible coloration.

Noise gates and dynamics compression/expansion including multiband dynamics modification can also help.

Noises related to power line hum can be easily removed with the DTMF filters in Cool Edit Pro and some if not all releases of Audition. I don't know if there is a DTMF filter plug in that could be used with Audacity, etc. but it would be worth looking for it.

Generally speaking fairly inexpensive LP playback gear can achieve needle-up SNR in excess of 70 dB. But it may take some messing with grounding and sources of radiated hum (such as wall warts with line transformers) to get there.

This post has been edited by Arnold B. Krueger: Sep 26 2013, 12:43
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uart
post Sep 26 2013, 13:23
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QUOTE (w1L50n23 @ Sep 25 2013, 18:57) *
Now, when I went to do my first test recording, I noticed some line noise bouncing the meters on the virtual soundboard (with no turntable connected yet).


Having nothing connected to those high impedance inputs is probably what's causing the noise. Try connecting shorting plugs across the inputs and then check it again.

A general purpose phono-in needs to have a combination of both high impedance and high gain, and that implies an inherent amount of thermal noise that is physically unavoidable (as in an actual physical limit that is unrelated to any implementation details or limitations of the circuitry itself).

For example if you have a 100k input impedance, a gain of 100 and a bandwidth of 30 kHz, then the (physically unavoidable) thermal noise is 100 sqrt(4 * 1.38E-23*298*100E3*30E3), which comes to about 0.8mV. Compared to a typical line level signal of 200mV this is about -48dB.

Even though this is a "physical limitation" with high input impedance, it doesn't mean it cant be overcome. You just need to connect the inputs to something of lower impedance, rather than leaving them floating.

This post has been edited by uart: Sep 26 2013, 13:24
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w1L50n23
post Oct 1 2013, 17:49
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Thanks all for the input (no pun intended).
I also switched PCI slots and nothing changed. Then I found this from Creative:
Inputs 3L/3R of the AudioDock and inputs 2L/2R of the MicroDock share with the RCA phono
inputs and have slightly more gain than other inputs. This means they are more sensitive to
noise than the other inputs on your external dock.
They therefore will show a little noise on the input meters because the meters are calibrated for
all the other inputs and not compensated for on the shared RCA inputs.
Mute them or delete the strip if you are not using those inputs.


This was mentioned by a couple of people.

I also had the phone strip created at 192,000kHz and rejigging to a more reasonable 96,000 made a dramatic difference.
So I didn't really solve it, but it looks as if there really wasn't anything to solve. I include this note for any that search and may find similar issues.
Thanks all.
Wilsen
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uart
post Oct 3 2013, 12:12
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QUOTE (w1L50n23 @ Oct 1 2013, 09:49) *
So I didn't really solve it, but it looks as if there really wasn't anything to solve. I include this note for any that search and may find similar issues.
Thanks all.
Wilsen

Have you measured the noise level with the turntable actually connected yet?
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