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FDP Forum / Performer's Corner / Low level hum on signal out of computer...

Tony Wright
Contributing Member

Stillwater, OK

I never met a calorie I didn't like.
May 24th, 2017 02:29 AM   Edit   Profile  

Offered as many of Roly's post, just bringing something to your attention that might help in the future...

Sometimes you don't have to be smarter than the other guy...sometimes, you simply evaluate what they did and did not try to resolve a problem and ask the stupid question about "did you try..."

We have had a low level hum on the signal coming out of the computer in the sound booth and into our mixer. To be honest, most all of our techs had just ignored that noise, including me...it is cramped and dark on the back side of the main house rack (DriveRackPA, graphic EQ, computer, CD/DVD player, A/C power source,and many other toys I forget.

We had an important client as they were paying quite a bit to get our 710 seat theater (with tech support crew) and dressing rooms for four days for their annual recital.

Shawn was working away on getting the system set up like he wanted the day before the event. I walked in to watch and ask a couple of questions on another project. I noticed the hum so I politely asked about the noise, thinking it was probably something he was causing while changing the configuration of the system.

He replied, "That is the hum that has been in it for several shows..." He went on to tell me all his efforts to kill that noise. He tried four brand new 3.5mm/TRS male to dual T/S 1/4 male plugs...he tried converting the 3.5mm into an XLR signal...and he tried a new AC power cable.

He went on working and I started going thru some of the other "out of the box" solutions....

"Hey, Shawn, I know you have probably already thought of this but...what about a couple of DI Boxes, one for each side of the stereo signal?"

Obviously, I would not have mentioned that if it did not work...it sounded fine and went thru the week end event with no problems.

Sometimes we are so close to the problem, we don't see the forest...or however that saying goes. Shawn was working on a different cable problem, so the hum (just a ground loop) was perceived as something he was already working on. In this case, it was a separate problem. Shawn stopped, thought and looked at me, "Can't hurt to try..." Worked like a charm.

SHOULD YOU find a buzz or hum coming from using a computer into your PA (cell phone; iPad; notepad; notebook, laptop?) Consider splitting your stereo out of the TRS 3.5mm into two sides of the signal (the stereo signal split to left and split to right) INTO a stereo DI Box or two mono DI boxes. It would be really nice if you had a ground switch on the DI's.

I will probably need to consider a couple more DI boxes for my own gear box. (Note to self, Ground Lift, Pad switch) I could wait for a sale and buy two more Whirlwind IMP2 DI. Cake and eat it too.

FDP Data Goon

We all want

our time in hell
May 24th, 2017 04:06 AM   Edit   Profile  

If computer, I'd just get a dedicated interface with actual monitor outs.

Juice Nichols
Contributing Member

Panama City, FL

I'm just a dude, playing a dude...
May 24th, 2017 07:13 AM   Edit   Profile  

Good info Tony!

Tony Wright
Contributing Member

Stillwater, OK

I never met a calorie I didn't like.
May 24th, 2017 08:53 AM   Edit   Profile  

Rev: I am not very "computer savvy"...I was born in the first half of the last century. I can guess what a dedicated interface is...when you talk about monitors...as in PA monitor speakers? Beyond that you lost me.

However, I suspect that I am not the only person on the FDP that was happy to learn that there is a way to "lift the ground" on a digital source at a gig where there is no tech support available from the IT guys. If there is a better way, fine. Maybe we need to look into that as a long term solution for the sound booth.

At work...we do lots of "talent shows." (Think frat and sorority doing fund raisers for Meals on Wheels and Big Brother and the Humane Society.)

University students who grew up in the "tech savvy era" will show up with songs recorded onto their cell phone from a band they heard in the club...or one recorded from the TV into their cell phone or notepad via a mic...

But for ME (my small sound for hire company) doing sound at a small wedding reception in the clearing in the wooded arbor running sound on a generator and a six channel small mixer with 2 wireless mics and a mp3 player that the client provided with their personally selected songs including the "specials" for the wedding march and during the ceremony and the recessional...I am surprised it took me this long to figure it out.

Contributing Member

Whitehorse Canada

I don't get out much
May 24th, 2017 03:22 PM   Edit   Profile  

We have four of these things.

Work great but the 1/8" TRS connectors are junk.
Replaced all of them before they were used.

laptop interface

FDP Data Goon

We all want

our time in hell
May 24th, 2017 04:15 PM   Edit   Profile  

No, as in an audio interface. Typically USB (Firewire on some Macs), they replace the junker computer soundcard.

You're using a tool that's going to have hum and issues for the wrong thing - it's a "Nobody uses built-in sound on a computer for serious things".

The audio interface will have X in, Y out, although you can just get a specific "out only" one for audiophiles as well. They'll have dedicated TS, TRS, XLR, and/or SPDIF outs.

Contributing Member

I've got my own

double-cross to bear
May 25th, 2017 09:12 AM   Edit   Profile  

GREAT info. A truly non-technical solution to a technical problem.

Thanks Tony!

FDP Forum / Performer's Corner / Low level hum on signal out of computer...

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