# Buzz when outputting to VGA projector



## StradivariusBone (Apr 24, 2015)

Trying to eliminate a buzz when I run audio from a laptop that is also connected to our projector (movies, slide shows, etc.). It's different than 60Hz hum that normally comes through ground loop issues, but I suspect the cause is similar. It goes away when the video cable is removed from the laptop. Is there a way to isolate he ground from the video line? The audio feed goes through a DI already, would an external sound card help?

Sorry if this has been covered elsewhere, I did search but couldn't find any best practices for this type of situation.


----------



## derekleffew (Apr 24, 2015)

Does the "buzz" happen when 
a) the source laptop is plugged into AC, 
b) when running on its battery, or 
c) both?
Does the laptop PSU have a polarized NEMA 1-15, or NEMA 5-15 male?


StradivariusBone said:


> The audio feed goes through a DI already


A "normal" DI won't solve anything. 

This http://whirlwindusa.com/catalog/black-boxes-effects-and-dis/direct-boxes/pcdi might. 
An external sound card via Firewire or whatever Apple's newest flavor this month would likely help.
I suspect this http://whirlwindusa.com/catalog/black-boxes-effects-and-dis/specialty-interface-solutions/iso-1 or http://www.sescom.com/product.asp?item=IL-19 will for sure.

An IL-19 and video humbucker should be in every AV technician's arsenal. An AC Ground Lift should never be.


----------



## StradivariusBone (Apr 24, 2015)

derekleffew said:


> Does the "buzz" happen when
> a) the source laptop is plugged into AC,
> b) when running on its battery, or
> c) both?



C- Both


derekleffew said:


> Does the laptop PSU have a polarized NEMA 1-15, or NEMA 5-15 male?



Both again. 

The laptop of choice today was a MacBook Pro with it's fancy (read: expensive) PSU with the NEMA 5-15 male and the other one frequently used is a NEMA 1-15 on an IBM ThinkPad. The ThinkPad is much nastier in terms of buzz, but that may be because it's old and crotchety. I've also experienced this buzz in another venue using a Mac desktop running a bunch of displays through ProPresenter. It's a weird buzz, not entirely unlike a ground hum, but definitely not your normal "garage-band-twenty-pedals-patched-into-a-Fender-amp" ground hum.

I have a DI that is similar in nature to the PCDI, but it only softens the hum. I've never seen a VGA video humbucker, I've heard of the type used to filter 75 Ohm composite. In any event I think I'll drop some bread on the IL-19 and the iso box, the video comes through clear with no interference.

To assuage your concerns with regard to ground isolation I refer only to signal ground, not AC ground. No one's getting zapped on my watch!

Thanks for the tips, Derek!


----------



## JD (Apr 24, 2015)

StradivariusBone said:


> It's different than 60Hz hum that normally comes through ground loop issues, but I suspect the cause is similar.


Maybe, but I think you have a bleed-over of the video/sync signal into your audio. Do the cables travel a distance together? The square-wave nature of the vertical sync signal means it has great capabilities of inducing signals in other cables. Try pulling the VGA connector from the laptop but allowing the shell to still be in contact. Chances are the buzz is not there even though the ground paths are being maintained.


----------



## auralpaz (Jun 26, 2015)

StradivariusBone said:


> Trying to eliminate a buzz when I run audio from a laptop that is also connected to our projector (movies, slide shows, etc.). It's different than 60Hz hum that normally comes through ground loop issues, but I suspect the cause is similar. It goes away when the video cable is removed from the laptop. Is there a way to isolate he ground from the video line? The audio feed goes through a DI already, would an external sound card help?
> 
> Sorry if this has been covered elsewhere, I did search but couldn't find any best practices for this type of situation.


Have you plugged the power of the laptop directly into a power conditioner as well as make sure your projection and sound have clean power as well? You might have already tried this but it seems to take care of 90% of the issues you're mentioning for m.


----------



## ruinexplorer (Jun 28, 2015)

Does the cable you are using have all 15 pins? You will see that many cables will be missing pin 9. This is an option to pass +5 volts, which you generally don't want. Otherwise, I completely agree that either using the video humbucker or the external sound card will be your best bet. Since you get the noise both when running on AC and on battery, my guess is that the noise is coming down the video line. Conditioning the power for the projector may work, but you will get best results with isolation (humbucker or external sound card).


----------



## rwhealey (Jun 29, 2015)

StradivariusBone said:


> Trying to eliminate a buzz when I run audio from a laptop that is also connected to our projector (movies, slide shows, etc.). It's different than 60Hz hum that normally comes through ground loop issues, but I suspect the cause is similar. It goes away when the video cable is removed from the laptop. Is there a way to isolate he ground from the video line? The audio feed goes through a DI already, would an external sound card help?
> 
> Sorry if this has been covered elsewhere, I did search but couldn't find any best practices for this type of situation.



Try picking up a Peavey USB-P - basically a rugged, driverless external sound card with XLRs out. I am thinking that the noise is probably poor shielding in the laptop instead of a ground problem.


----------



## StradivariusBone (Jul 28, 2015)

Update- Bought an IL-19 and was unfortunately disappointed in it. It did a little bit to reduce the noise, but did not eliminate it. Going the Peavey USB-P route and investigating the power situation at the projector next. The VGA cable is indeed missing pin 9 btw.


----------



## rsmentele (Jul 29, 2015)

I Really like the PCUSB from Whirlwind. I find that I often get a buzz from the headphone jack, even when I use a PCDI, but with the USB connection, the signal is much cleaner. The only thing is that it's not always plug and play. On some computers you have to go into your preferences and select it as an audio device.

http://www.fullcompass.com/prod/261592-Whirlwind-PC-USB


----------



## StradivariusBone (Sep 21, 2015)

Just wanted to update this thread to finish up. I ended up getting the Peavey USB-P and was incredibly pleased with the result. It syncs up quickly with the laptop and outputs super clean with very little noise. I haven't tried it with OSX yet, my work macbook has some dumb issue with the USB Audio Codec not working. It has a demo version installed and will beep every 30 seconds. But I think the Peavey uses another route to output. 

It also outputs balanced line level. Which is nice.


----------



## TCJ (Sep 21, 2015)

Might be a little late to this thread, but regarding the DI you tried... I am curious... did it have a "ground lift" (or "ground isolator" or "ground disconnect") switch? (If not, the only alternative for eliminating ground noise is to use a balanced audio cable wired so the ground/shield remains "floating" at one end.)

Though from what I read, I too suspect the noise was not a ground problem. Sounds more like the analog circuitry in the laptop's onboard audio system was picking up noise from the video signal / video cable. I think outboard audio peripheral is the only way to go in that case.

Curiosity #2: What exactly is beeping every 30 seconds? The _drivers_ for this thing?? Or some separate audio processing application? (Assuming the latter, wouldn't it beep then no matter what audio device you use, be it the computer's built-in, or the Peavey unit?)
I'm far more familiar with Windows than Mac, but from my experience with a few outboard audio devices, they install drivers with pretty much the same APIs as the computer's onboard audio. So you can keep using all your same programs/applications as before... but with the outboard device now.


----------



## StradivariusBone (Sep 21, 2015)

The several DI's I tried did have ground lifts, one was a powered DI. The projector is plugged in on the catwalk, so it's possible that there is a potential between the audio system ground and the regular outlets. Tried a Pin 1 lift, nothing. 

Switching laptops didn't help either. Had a Lenovo and a MacBook, both noisy (the older Lenovo much more so). I bought this box- http://www.amazon.com/dp/B000BBGCCI/?tag=controlbooth-20 hoping that it would help, but it proved incompatible with my MacBook. Very long story short-

It runs using a piece of software called USB Audio Codec. Apparently it's stock with 99% of all OS's in the world. My MacBook however has a demo version of it installed and so every 30" it will beep on the output channel. I tried finding a replacement, but the only source I could find is a super old website that wants me to buy the codec that should be on my machine already. I've found many people online dealing with this issue but of course no solutions from Apple. If anyone could share some insight I would be ecstatic. 

The Peavey uses a different audio engine so it should be fine.


----------



## dbaxter (Sep 21, 2015)

Did you take a look at ffmpeg for audio codecs? If it was Windows, I could help you directly, but that site says there is an OSX version available.


----------



## StradivariusBone (Sep 22, 2015)

I just tried fiddling with that, but it wants to run a bunch of command line stuff, and on Mac/UNIX I'm very green. The big difference (and the issue I'm having) is in my understanding of how Windows uses drivers and codecs and how Mac uses them. Macs don't use drivers in the same way (or from what I can tell at all) and I can't explain it, but it was where I was hitting the brick wall in my Google-Fu on this one.


----------



## dbaxter (Sep 23, 2015)

You might get better descriptions of codec usage on a Linux wiki of the subject. Those folks divulge everything and OSX is, afterall, a variant of Linux. I poked around a bit, just for my own knowledge, and came up with this: http://m.download.cnet.com/Digidesign-CoreAudio-Driver/3000-2120_4-43417.html. From what I read, Macs use this CoreAudio interface. But you probably already know all this. Sorry if this is all deja vu.


----------

