Mac DVI/VGA adapter interfering with sound?

[Soovey]

Right now we're using my MacBook Pro, as our PC died, but I have an iMac on the way. Only one problem. We're also trying to set it up so we can play sound from the comp to the soundboard, but we keep getting a buzz. When we unhook the DVI/VGA adapter the buzz disappears. Anyone got a clue what to do? Also, what cable would you suggest to hook the comp to the soundboard? It needs to be about 20-25 feet.

[Nathan J]

Laptops often have lots of sound interference and noise issues with sound systems -- try unplugging the power supply on the Mac (letting it run on battery) and seeing if the buzz goes away.

I use an external USB sound interface to connect our Macbook to the mixer -- not only does it eliminate noise, it gives pro level outputs instead of 1/8". Might be a good solution for your iMac too.

[zactommo]

Sounds like the projector, or whatever your using for a display isn't on the same earth as the PA, or has dodgy earthing. Running the sound feed to the PA through an audio ISO transformer, or connecting your projector to the same power source as the PA would probably fix your issue.

[cmchamp]

I've been using Macs since '86. The only time I have issues with interference is when the Earth Ground is messed up on another circuit or another device.
For instance, I recently moved my PA at school to another circuit. Now, the local AM station bleeds in and it's even more prevalent when I attach the Cat5 network cable.
This is power adaptor independent.
In general, Mac hardware has exceptional RF rejection.
On that note, when you do experience hum, noise, RF bleed when introducing any computer or other device to your system, is assure proper ground, proper interconnect cables.

[petereit]

Though it would require a D/A converter at your board, you could connect a standard Toslink cable with a Toslink mini-plug adapter to your MacBook and get a digital optical out. Should be pristine signal with absolutely no noise.

[JoshGuerette]

Personally, I've never been able to get audio/video to work well simultaneously on my MBP. I don't know the specifics, but I've heard that the audio board is to blame. At the very least, it has a noticeable hiss.

[macjunkie]

I am using a radial multi-media DI box it has 1/4", RCA, and 1/8" inputs and stereo XLR outputs. I have to lift the ground and it removes the buzz. I think its a great solution to the problem.

[benwilhelm]

Originally Posted by macjunkie

I am using a radial multi-media DI box it has 1/4", RCA, and 1/8" inputs and stereo XLR outputs. I have to lift the ground and it removes the buzz. I think its a great solution to the problem.

I've found that sometimes a ground lift on a DI isn't enough and an isolation transformer is needed, as others have mentioned. I too concur that it's a power/ground related issue. Haven't seen any bad advice in this thread yet!

Ben

[Soovey]

Using a RCA to 1/8" cord, the sound works perfect with our new iMac, and now we have sound to work with our new shiny Pro Presenter 4, that leaves one very happy techie who no longer has the dreaded blue screen while switching between computer and video to play DVDs or clips. ^_^

Thanks for everyone's help! I'll probably have more questions later, as we need a new light system and probably work on our horrible sound system. :/