Buzz or Hum in Audio Port

Update -- it quit.

I was taking my MBPro in to an Authorized Repair Shop for an unrelated problem, and I thought I'd mention this there, so I tested with headphones to be sure I could demonstrate the problem. I couldn't. It all worked fine. I didn't do nuttin'.

Well, actually, I did run Repair Permissions sometime in the past. David Anderson17 on another thread said that might've been what worked for him:

Thanks for your comments. I solved this buzzing problem as a result of one or more of the following procedures:

Runing the Onyx cache cleaner on default list plus system.cache.

Deleting the iDVD.plist

Running the permissions repair utility (DiskUtility)

Then again, it could have been one of those Software Updates. Someone prolly knows.

--Gil

Thanks for the comment, Poikkeus. The buzz does sound indeed like like a ground loop, but does not change when I plug in the power supply via the Magsafe adapter, nor does it change when I move the headphone wires around, or move the computer around, as you would expect for incidental electrical noise.

Now, this hiss you're talking about, that I do not hear. There are a couple of seconds after I plug in the headphones before the computer detects them. During this period the sound continues to come out the little built-in speakers. But the headphones are silent during this period; no hiss for me.

Evidently that either-input-or-output-but-just-one-at-a-time audio jack has some curious quirks. Not too surprising, when you try to imagine what must be going on behind that little hole in the case.

--Gil

Hi, fane_j--

What MBP are you talking about?

Well, System Profiler puts it this way:

Model Name:	MacBook Pro
Model Identifier:	MacBookPro5,5
Processor Name:	Intel Core 2 Duo
Processor Speed:	2.53 GHz
Number Of Processors:	1
Total Number Of Cores:	2
L2 Cache:	3 MB
Memory:	4 GB
Bus Speed:	1.07 GHz
Boot ROM Version:	MBP55.00AC.B03
SMC Version (system):	1.47f2

It has just one 3.5mm + S/PDIF audio port, called "Combination Output" by System Profiler, used for either input or output, depending...

Intel High Definition Audio:

Audio ID: 77

Headphone:

Connection: Combination Output

Speaker:

Connection: Internal

Line Input:

Connection: Combination Input

Internal Microphone:

Connection: Internal

S/PDIF Optical Digital Audio Output:

Connection: Combination Output

External Microphone / iPhone Headset:

Connection: Combination Output

Headphone:

Connection: Combination Output

Speaker:

Connection: Internal

Line Input:

Connection: Combination Input

Internal Microphone:

Connection: Internal

S/PDIF Optical Digital Audio Output:

Connection: Combination Output

External Microphone / iPhone Headset:

Connection: Combination Output

Does this answer your question?

--Gil

I hear the buzz in analog out mode. I have not yet figured out how to determine what's coming out of the digital out port, although that's a very good question. Perhaps I can figure out a way to test that.

--Gil

Hi, Helene.

I decomissioned the Hi-Fi loudspeaker connection to my MacBook Pro. I use only headphones now with that port, and I do not hear the hum. I guess you could say that I gave up or gave in.

Incidentally, I do use the sound output port on my Mini in the living room to connect to the living room's Hi-Fi system. On that setup I do not hear the hum, even though I often have the volume turned up while watching a movie. I think that Mini has separate "earphone" and "microphone" ports, so it's not the same setup.

The hum seems to me to be an artifact of that wondrous jack on the MacBook Pro. I have used it with a 4-conductor plug to carry both headphone and microphone signals in full duplex with, e.g., Skype. Amazing flexibility, very ingenious, but produces a hum on the Hi-Fi. Ah, well.

--Gil

I'll just finally break down and get a proper DAC.

When you do, do let us know which one you chose.

--Gil