Audio static noise

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kell_vern
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Audio static noise

Post by kell_vern » Tue Mar 22, 2016 4:19 am

We have this noise issue for months now in our booth, everything had grounded already but this noise keeps appearing.
This came from our audio source (PC), but if we put the PC into UPS mode, the noise disappears.
Can somebody help me what to do? Is this AC lines related? (PC uses servo type AVR)
TIA

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Dale H. Cook
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Re: Audio static noise

Post by Dale H. Cook » Tue Mar 22, 2016 6:10 am

kell_vern wrote:... everything had grounded already ...
Is it correctly grounded? Are you using star grounding with a good (low impedance) ground reference? Are shields grounded only at one end?
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kell_vern
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Re: Audio static noise

Post by kell_vern » Tue Mar 22, 2016 7:19 am

Dale H. Cook wrote:
kell_vern wrote:... everything had grounded already ...
Is it correctly grounded? Are you using star grounding with a good (low impedance) ground reference? Are shields grounded only at one end?
-Is it correctly grounded? >yes
-Are you using star grounding with a good (low impedance) ground reference? >star grounding yes
-Are shields grounded only at one end? > what does it mean?

while in UPS mode, noise disappears, what happened in this situation? can u explain sir? thanks

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Deep Thought
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Re: Audio static noise

Post by Deep Thought » Tue Mar 22, 2016 7:48 am

You'll have to explain what you mean by "UPS Mode". Is the entire studio on backup power then? Or just the computer? What is powering the system in "UPS Mode"?
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kell_vern
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Re: Audio static noise

Post by kell_vern » Tue Mar 22, 2016 8:17 am

Deep Thought wrote:You'll have to explain what you mean by "UPS Mode". Is the entire studio on backup power then? Or just the computer? What is powering the system in "UPS Mode"?
-if i use the UPS (Uninterruptible power supply) for the PCs for a few seconds, the noise disappears.
-no.
-just the PCs.
-the UPS..

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Dale H. Cook
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Re: Audio static noise

Post by Dale H. Cook » Tue Mar 22, 2016 9:03 am

kell_vern wrote:-Are shields grounded only at one end? > what does it mean?
As a rule the shields on the audio cables should be grounded at only one end of each shield. The common method is to connect the shield drain wires to signal ground at the load ends, and to leave the other ends of the shields floating. That prevents ground loops. As a rule you do not want to ground both ends of a shield unless experimentation shows that it is needed to minimize noise.

Are all of your audio cables balanced, truly balanced? Some equipment has inputs or outputs labeled + and -, but the - terminal is actually ground. Some studio equipment was made that way, such as the original Orban 622 parametric equalizer. The output terminals were labeled "Hi, Lo, Gnd." The "Gnd" terminal was chassis ground, and the "Lo" terminal was signal ground.

This may all be moot. Following up on Marc's response, what make and model of UPS are you using? If it is not a true uninterruptible power supply, but is actually a standby power supply, it could be that the battery charger is putting out hash.
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kell_vern
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Re: Audio static noise

Post by kell_vern » Tue Mar 22, 2016 9:14 am

Dale H. Cook wrote:
kell_vern wrote:-Are shields grounded only at one end? > what does it mean?
As a rule the shields on the audio cables should be grounded at only one end of each shield. The common method is to connect the shield drain wires to signal ground at the load ends, and to leave the other ends of the shields floating. That prevents ground loops. As a rule you do not want to ground both ends of a shield unless experimentation shows that it is needed to minimize noise.

Are all of your audio cables balanced, truly balanced? Some equipment has inputs or outputs labeled + and -, but the - terminal is actually ground. Some studio equipment was made that way, such as the original Orban 622 parametric equalizer. The output terminals were labeled "Hi, Lo, Gnd." The "Gnd" terminal was chassis ground, and the "Lo" terminal was signal ground.

This may all be moot. Following up on Marc's response, what make and model of UPS are you using? If it is not a true uninterruptible power supply, but is actually a standby power supply, it could be that the battery charger is putting out hash.
the pc sound card was a digigram with XLR outputs to the inputs of 12000 Arrakis console.
other pc was just on board soundcard to a 3.5mm audio jack > RCA jacks to the inputs of 12000 arrakis console.
the UPS was an APC,i forgot the model.
is this not related to the AC lines? because sometimes, this wont appear..

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Dale H. Cook
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Re: Audio static noise

Post by Dale H. Cook » Tue Mar 22, 2016 9:56 am

kell_vern wrote:the pc sound card was a digigram with XLR outputs to the inputs of 12000 Arrakis console.
That should be okay. Although I don't much care for Arrakis consoles the inputs are active balanced.
kell_vern wrote:other pc was just on board soundcard to a 3.5mm audio jack > RCA jacks to the inputs of 12000 arrakis console.
That is an unbalanced source feeding a balanced load. Is the shield tied to both the - input and ground at the Arrakis input?
kell_vern wrote:the UPS was an APC,i forgot the model.
I do not recall ever seeing an APC that was an actual UPS. It is almost certainly a standby power supply, where the load is fed by the battery through the inverter only when mains power is off.
kell_vern wrote:is this not related to the AC lines? because sometimes, this wont appear..
It may well be. The APC disconnects the load from the mains when it is online, so you may well have mains-conducted noise. If you have multi-phase mains service, is all of the studio equipment fed from the same phase of the mains?

You could have something like an HVAC blower that is putting out hash. Potential noise makers, if possible, should not share a mains phase with studio equipment. When you experience the noise try walking around the physical plant with a portable AM radio. Sniff around the physical plant with it, rotating the receiver for strongest noise, to try to see where the hash is strongest. I would use my portable Sangean receiver with a tunable loop antenna to try to get a null bearing on the noise, but I suspect that you don't have anything that sophisticated on hand.
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kell_vern
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Re: Audio static noise

Post by kell_vern » Tue Mar 22, 2016 10:14 am

yes UPS, just a standby power. and i dont have that tools.
we use single phase. can this be resolve with hum eliminator?

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Re: Audio static noise

Post by Dale H. Cook » Tue Mar 22, 2016 11:28 am

kell_vern wrote:can this be resolve with hum eliminator?
Perhaps, but first you need to determine where the interference is coming from.
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Re: Audio static noise

Post by TPT » Tue Mar 22, 2016 5:07 pm

We had a similar problem with a kind of "hash" noise showing up on the input to our STL transmitter. As best as could be determined, the noise was "RF like" coming in on the power lines (you could hear it on FM on a car radio out in the parking lot by the power pole--but not on AM). More frustrating--it would appear for a week or so, then vanish for months.

First problem found: No RFI filtering on the STL (Armstrong) AC input. Chopped a power cord in half and ran it through a Corecom filter mounted in a metal box. Cut down but did not eliminate the noise.

Next we put in a power conditioner (Tripp Lite LC1800) to feed most of the critical equipment in the rack. Also helped. Then we found a refurbed UPS that was active--that is, the device used an inverter that was always on, while the AC input kept the batteries charged. Bingo--noise gone.

Never did find the source of the noise. We're in a mixed commercial/residential area--best guess, something in the HVAC plant of a large church near us.

In this case, I would try the power line conditioner first to see if it helps. Also--follow the power conditioner with a plug-in surge suppressor (such as in a small outlet strip)--this sometimes helps to eliminate hash on the AC line. Run both the computer and monitor off the same AC feed--if you use a an unbalanced to balanced "direct box"on the audio output power that off the same AC feed.

kell_vern
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Re: Audio static noise

Post by kell_vern » Tue Mar 22, 2016 7:56 pm

thanks for the input sir(s)...
i'll let you know the results with these solutions.. :D

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Re: Audio static noise

Post by ChuckG » Wed Mar 23, 2016 8:10 pm

Dale H. Cook wrote: what make and model of UPS are you using? If it is not a true uninterruptible power supply, but is actually a standby power supply, it could be that the battery charger is putting out hash.
That would be the absolute first thing I'd try. Take the UPS out of the circuit, unplug it and shut it off. Plug the computer in directly. I've had the internal battery charger in a UPS do what you are saying. (it was a Tripp LIte AVR type unit)
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