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Authored by: pascalpp on Oct 22, '02 12:37:28PM

i'm using one of the new G4s as the center of an audio workstation using logic as the software and a fair amount of external hardware. the G4 sound out is running into my mackie mixer board and then out to my audio monitors (mackie HR824s). when i turn up the volume for the system sound on the mackie mixer, i hear a very strange staticy hum. is this the feedback sound you're talking about?

my setup is kind of complicated (the computer is actually in another room, with all the cables passed through a hole in the wall), but i didn't hear this static sound with my old G4 in the same setup. fortunately all my audio production is done using a MOTU 828 firewire I/O unit, so the static doesn't appear in my recordings, but it is annoying nonetheless when i'm listening to iTunes or playing quake or what have you.

could you provide a link to the tech article you mentioned?



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Authored by: DavidRavenMoon on Oct 22, '02 09:58:43PM

A scratchy sound is just interference from the radio producing parts inside the Mac. Or it can also be what's known as "DC offset," which is where there is a DC voltage along with the AC audio signal in the audio path. A ground loop, which is what Apple is referring to, sounds like a humming or buzzing noise.

You should never use the built in audio jacks for anything important. The Mac is filled with all sorts of interference inducing circuitry. I use an M-Audio Audiophile 2496 and it sounds great, nice and quiet.

Another way around ground loop problems is to make sure every piece of gear is plugged into the same outlets. If you have equipment with three pin grounded plugs, use adapters on the AC plug to "lift" the third pin, you know, the kind used to plug into the old 2 pin wall sockets. Only leave one power cord, the Mac, grounded.

Another strategy is to make new patch cords with the shield grounded only on one end, and plug that end into the Mac. This way you avoid the ground loop.

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Authored by: sly808 on Oct 24, '02 03:42:57AM

Just go to the Apple website and click on the support link. In the text window, type in "G4 Speaker Problem" and the article should come up. I just bought a new G4 last week and noticed this problem right away, even when using headphones connected to the jack up front. What bothers me is that Apple knows about this but to fix it you have to spend another $15 on top of the 2 or 3 grand that you spent for the machine in the first place. For that kind of money, this G4 should have zero problems.



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