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Brian Sahlin
Audio white noise issues.
on Sep 15, 2014 at 1:18:18 pm

I recently started a new job as audio technician for a company that contracts with a federal government facility. Essentially the project is live streaming training/educational videos through wirecast and into an Amazon cloud environment. I am using a PreSonus StudioLive 16.4.2 audio mixer. We are still in the testing phase and haven't began the live events yet.

I have come across two audio issues.

1. We have 2 laptops connected for video playback/music/skype. The audio comes from a 1/8" stereo jack out of the laptop into a RapcoHorizon LTIBLOX adapter into an XLR cable and into the audio mixer. With the gain set a unity and the main mix fader up, i am getting a -80-60dB signal. When I turn the monitors up there is what sounds like an electronic buzz that I would like to get rid of.

2. The other issue is during the live feed. If we start a broadcast with all the channels on my audio board muted then it is completely silent. If I unmute a channel, even if there is no lav mic turned on, there is a fuzzy sound. It is different than the sound in issue 1. The best way I can describe it is like on old VHS tape sound. It is not at all present in the audio monitors nor if I listen through headphones on the audio mixer. Nobody involved in the testing as mentioned it, as it's nearly negligible as long as someone is talking, but I personally know it can be better/cleaner.


I should mention that this is not at all a professional studio setup. They basically converted an office full of cubicles into a "control room" that is much more cramped than it should be. Supposedly, they are looking to move into a building 10 times the size of this one and have 3 actual studios designed/set up, but that wouldn't be until June. This was all set up by a previous contractor.

I appreciate any advice and help.


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Bill Davis
Re: Audio white noise issues.
on Sep 15, 2014 at 5:48:49 pm

Without hearing these noise issues it's harder to diagnose them.

Presuming that the cable buzz in 1 is some kind of inducted hum, then I'd try dumping the cheap Rapco thing and just use one of these: http://tinyurl.com/ma9yxhv. I've taken feeds from my laptop, iPads, iPods and all manner of things with 3.5mm headphone jacks and its simple and works great.

If the problems is an RF issue in the space or a bad ground somewhere, then it's not going to work. But it's cheap enough to try and these cables are smart to have around since so many things have only headphone jacks as an output port.

Same issue with the second question. Without hearing it, it's hard to know where to begin.

Know someone who teaches video editing in elementary school, high school or college? Tell them to check out http://www.StartEditingNow.com - video editing curriculum complete with licensed practice content.


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John Fishback
Re: Audio white noise issues.
on Sep 17, 2014 at 8:44:28 pm

This could be a result of ground loops. If any of the devices have 3-pin ac plugs try ground lifts and then run a ground wire between all devices. Another trick is to lift the shield from one end of a cable. The shield needs only be grounded at one end to work, but when you do this, it's important to have each device grounded independently. In professional audio rooms "star grounding" is used. That means all cables have lifted shields, but all devices have a dedicated ground wire that's run to a common "star point" ground.

John

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Brian Reynolds
Re: Audio white noise issues.
on Sep 15, 2014 at 10:49:10 pm

Problem 1 is often caused by the laptop power supply, switch mode supplies often cause this problem, Try running the mixer + laptop power supply, or try different ways of outputting the audio like USB interfaces, if all else fails run it on batteries. Apple laptops often have the worst problems.

Problem 2 sounds like a 'gain staging' problem in the audio chain. ALL the levels in each stage must be correct to achieve good results.


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