My MBP hisses when I connect it to my TV. Why?

October 9, 2006 8:17 PM

Why does my MacBook Pro hiss/bubble when I connect it to the TV (not the logic board thing, I've done that)?

So I use my (2gig ram, 2.16 processor) MBP to watch films, dvds etc through my TV. I use the DVI-S-Video doohickey and a standard 3.5mm Y cable from the headphones socket.

Whenever I connect the system up, there is a constant hissing/bubbling sound through the TV's speakers.

It is incredibly annoying and sounds like the Logic Board problem did (through the right speaker), before I got that fixed. Was kind of hoping it was the same problem and all would be well when I got a new logic board. Ah well.

The sound is worse when the processor is doing lots of work and is realtively quiet when it isn't so busy. What is causing it, can I solve the problem?

I wonder if it's something to do with completing a circuit or something (sorry for the crappy terminology!). When I detach the audio cable, if I touch more than one of the posts on the plug with my fingers, I get audio feedback through the TV's speakers. Is that connected?

posted by tonylord to computers & internet (4 comments total)

Does it make the sound when you've got headphones plugged into the same jack? If not, try a different cable to the TV.
posted by jjg at 10:18 PM on October 9, 2006

It sounds like a grounding issue. Some things to try:

1) Make sure the macbook and TV are plugged into the same AC outlet as the stereo system.

2) Buy a ground loop isolator from Radio Shack ( I think they're about $20), and place it between the macbook's audio out and the input on the stereo.

3) Try maximizing the volume on the macbook and turning down the volume on the stereo. If you can't get rid of the noise, this will at least minimize it.

Also, I believe that Macbooks have optical out (you have to buy an optional adapter from the Apple store). If your stereo has optical input, then using the optical connection will solve your problem.
posted by helios at 10:21 PM on October 9, 2006

You could also try picking up a Griffin iMic, which is a USB audio out/in adapter thingy. It works with OS X without any drivers and you can grab one on eBay for about fifteen bucks. Since the sound wouldn't be routed through the regular audio system it wouldn't pick up any of that noise.

(Not that the system should be making that noise in the first place...but I couldn't even begin to diagnose what's wrong with it)
posted by bcwinters at 6:48 AM on October 10, 2006

I have this problem with an MBP out to some high powered amps through the analog minijack. To get around it, I turn off one of my cores and it goes away. (You can turn off a single core dynamically using the "CHUD" tools, which come with the Developer Tools. It creates a Processor prefpane in SysPrefs.)

This is not a real solution, but it works in a pinch. My real answer is more like the guys above, it's an issue with impedance or a ground issue or something else. I am guessing this because other amp/speaker systems I hook my MBP up to do not have the awful noise.
posted by neustile at 7:17 AM on October 10, 2006