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Electrical Noise...

RayDunzl

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I have a 25 foot cable from the analog outputs of my preamp to the PC for taking comparative measurements with the mic feed from the room.

Three baselines with no signal present below.

1) Noise floor internal to the on-board Realtek PC sound stuff :

upload_2016-11-12_18-39-37.png



2) The input from cable from the PC to the preamp:

upload_2016-11-12_18-40-32.png



3) The input from the cable from the PC to the preamp with a plasma TV turned on:

upload_2016-11-12_18-41-27.png



4) Noise floor of UMIK-1 (USB measurement mic). PC fan noise at 120/200 Hz area.

upload_2016-11-13_13-54-44.png
 
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RayDunzl

RayDunzl

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I am not quite clear what you are measuring.

In this case, just showing the noise floors associated with an analog cable from the PC to the preamp, with which I can monitor a source signal and compare it to the in-room signal.

There is a 25 foot cable but what does it plug into on the PC? Is it the analog to digital converter on the PC?

Yes. It is plugged into one of the reassignable 5.1 jacks on the motherboard, which can be selected as an input to REW.

upload_2016-11-12_20-54-13.png
 
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Vincent Kars

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I assume it is the cable picking up the noise.
Do you have one with a better shielding?
 

Speedskater

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Some good 'long' unbalanced interconnect cables are:
Canare LV-77S
Belden 1505F or 1695A
Blue Jeans Cable LC-1

**********************************
You might try turning on/off or unplugging (especially wall-worts) other:
a] audio components
b] appliances
c] high tech lighting systems
d] other entertainment systems
e] data (computer) systems

And see how that affects the noise.
 

Vincent Kars

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"You might try turning on/off or unplugging (especially wall-worts) other:
a] audio components"

a] indeed solves the problem :)
 

Keith_W

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Let me see if I have figured this out correctly?

1. Noise measured at the motherboard output?
2. Noise measured at the preamp input (i.e. motherboard output + 25 foot cable)
3. Noise measured at the preamp input but with plasma TV on

That 25 foot cable of yours certainly appears to be picking up a lot of stray noise.

Do you think that the added noise from the plasma TV comes from noise injected into the power supply (and thereby into your motherboard), or do you think it comes from poor shielding of the 25 foot cable, which is running too close to the TV or power lines? Out of curiosity, do you get less noise if you were to move the cable so that it is further away from the TV?
 

DonH56

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Is the cable's other end floating (unconnected) or attached to the preamp? If the latter, is the preamp on? Also if the latter, what happens if you move the preamp closer and use a short (e.g. 3') cable instead?
 
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RayDunzl

RayDunzl

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Is the cable's other end floating (unconnected) or attached to the preamp? If the latter, is the preamp on? Also if the latter, what happens if you move the preamp closer and use a short (e.g. 3') cable instead?

I won't be moving anything, at least until it comes time for a major cleanup... The cable has a couple of feet of slack, runs under the rug on top of the carpet along with a powered repeater USB cable (to the DAC), optical cable, another USB cable (no repeater, to the miniDSP), and maybe another unconnected analog cable.

Wow, looking now, there are 8 cables running under the rug PC to rack, I can only remember what 4 of them do, some must be superceded/disconnected.

---

The first "measurement" is made by selecting "Stereo Mix"

upload_2016-11-13_13-0-47.png


in REW as the input with nothing playing to or from or in the PC - whatever that really means. Amirm might remember. If I play a video on YouTube through the PC speakers the audio shows up on this internal "input".

The second measurement is with REW set to monitor "Line in at rear panel(Orange)"

upload_2016-11-13_12-56-58.png


into which is inserted the cable below from the Zone 2 output of the preamp with everything that is normally on, turned on, lacking only a spinning disc in the CD player, which would make an analog signal to the Source 2 input of the preamp, which would route that input to the Zone 2 preamp out. Also "powered on" are the HDRadio, DAC2, Behringer DEQ2496, Cable DVR Box, amplifers, Oppo (standby), niniDSP Open DRC-DI, an ethernet switch, and Audio Authority 1177A switch at the rack side, and PC, external drive caddy, idle Canon USB scanner, idle powered speakers, APC UPS, two flourescent LG monitors, Cable Modem, wifi router, Ooma telephone base, and an idle Brother Laser printer,

The third measurement is the same as 2, but with the TV turned on showing pictures of Big Brother glaring at me, no, wait, it was Election stuff.

---

The cable is a cheap (but heavy) twin RCA to stereo 1/8 that claimed shielding and cost $10 or so delivered...

Looks like this:

upload_2016-11-13_12-45-27.png


Do you think that the added noise from the plasma TV comes from noise injected into the power supply (and thereby into your motherboard), or do you think it comes from poor shielding of the 25 foot cable, which is running too close to the TV or power lines? Out of curiosity, do you get less noise if you were to move the cable so that it is further away from the TV?

The TV plugs into the Equitech (isolation, balanced AC power) along with everything else at the rack side, the PC is across the room and plugged into a UPS. It all comes off the same breaker, which is about 80 cable feet (25m) away on the wall in the Used Car Department.

As to what is interfering with what, since it's a big mess of wires and a big lump of gear, is pretty much anybody's guess. I just thought I'd show a picture of three idle measurements. There's no audible consequence that I can detect.
 
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amirm

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Thanks Ray. I will try to duplicate your results and see what I get.

For now, here is a great video on how noise can leak into sensitive devices from non-obvious sources. It is not too technical even though it is from Dave Jones and worth a watch:

 

fas42

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Noise, the final frontier ... worrying about issues like this is exactly what I do to get the jump in subjective quality that I talk of. The noise is not directly evident, as being audible, but the impact certainly is - it cripples the quality in subtle ways so that the replay sounds like hifi, not the "real thing". This is not "pop and crackle" stuff - this is, "boring, flat, uninteresting sound - I can't be bothered listening to it" impact.
 
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RayDunzl

RayDunzl

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here is a great video

I just took all that in.

I was hoping he'd have to figure out how to get the battery out of his wristwatch, or try and show us it was actually coming from the camera.

"Look! When I turn of the cam -------------------------------------------------------------- and there it is again!"
 
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