Audio playback problem on Mac Pro 2010

[powerless]

I am having audio playback distortion on my 2010 Mac Pro. When I am listening to (mostly) music there is a very subtle but noticeable distortion in the playback. The distortion does not last even a second but it can happen at least once every five minutes. Playback is of audio (mp3, m4a) through iTunes. I have tried with VLC and the distortion is still present.

I say mostly music as I do listen to podcasts, movies etc and if it is happening with these then I cannot hear it.

To try and solve this I have tried the following...

• Installed original Apple RAM.
• Reset NVRAM and PRAM.
• Re-installed ML (10.8.2) - with no other software installed.
• The Audio files have been on different hard drives - maybe it was a HDD on its way out, but I doubt all four of them are.
• Removed all internal cards, HDD and ran with only the boot drive.
• As above but with another drive.
• Plugged the Mac into a different mains socket.
• Unplugged my monitor - not sure why it just seemed a good thing to do.
• Unplugged all peripheral devices.
• Re-downloaded songs via iCloud - maybe I had a problem with the actual files. However as the files are from iTunes, Amazon, Play.com, CD rips etc I ruled this out.
• Plugged my headphones and speakers into the front audio jack (I usually have it plugged in the rear).
• As above but with another set of known working headphones.

Needless to say none of the above worked.

Then comes AppleCare - who didn't actually get me to do a lot. As I have tried all the above they only had me remove two plist files from Boot Drive/Library/Preferences/Audio but it didn't work. The files were not recreated on a reboot and with the files missing iTunes always froze.

The Mac Pro was sent away for repair where it had its logic board replaced which didn't make one bit of difference.

A few days later it was sent away for another repair where it had the PSU, GFX Card, processor tray, (I think CPU) replaced. It once again did not make one bit of difference - within fifteen or so minutes I could hear the audio playback problem. It was actually returned to me today.

In total the Mac Pro has been away for repair for one whole month.

Before I phone AppleCare yet again am I missing something obvious?

Any ideas?

 

[Tesselator]

Wow, I would have guessed a bad cable 1st. Then maybe a cold solder somewhere, Then lastly a faulty chip. But you say:

• Plugged my headphones and speakers into the front audio jack (I usually have it plugged in the rear).
• As above but with another set of known working headphones.

The Mac Pro was sent away for repair where it had its logic board replaced which didn't make one bit of difference.

A few days later it was sent away for another repair where it had the PSU, GFX Card, processor tray, (I think CPU) replaced. It once again did not make one bit of difference - within fifteen or so minutes I could hear the audio playback problem. It was actually returned to me today.

So that's not it - unless they lied about the repairs of course. So I'm stumped. Damn, tough one...

LOL I wonder if it's possible that RF or MW could be the cause and it's actually location based. Know how to create a faraday cage?

 

[powerless]

LOL I wonder if it's possible that RF or MW could be the cause and it's actually location based. Know how to create a faraday cage?

I have moved it to the opposite side of the room - different power socket, no Ethernet as well with doing this. Still the same. Do they make big bird cages ?

It's been located in its current position for 2.5 years with no trouble. I cannot think of anything new in this house at least.

 

[Tesselator]

I have moved it to the opposite side of the room - different power socket, no Ethernet as well with doing this. Still the same. Do they make big bird cages ?

It's been located in its current position for 2.5 years with no trouble. I cannot think of anything new in this house at least.

Well let me preference by saying this is highly unlikely in the first place but... If it was something like MW bursts causing the trouble it would probably be from someplace a ways away and not too near or inside your house. I have read about strange cases... but again; what are the chances... Pretty close to nill I would think. Repositioning the machine within the same house may or may not affect such a problem. Pretty easy to find out I guess. Bring the machine over to a friends house or something and give it a try there (the further away the better). Leave your cell phone at home when/if you try this.

 

[MacProFreak]

I would try to troubleshoot this doing the following, using a headphone you know works fine tested somewhere else:

1) Put an audio CD in and play it using your favorite player. Don't rip it. Make sure the volume setting is half way up. Don't put it to max. If you don't hear distortion from playing a CD, this means your core audio is working fine.

2) Rip one song from the CD (iTunes is ok) but have it do it saving the file as WAVE audio, 44.1KHZ, Stereo, 16 bit.

3) Listen to that ripped audio file using your favorite player. If it doesn't distort, it's one more sign that your core audio is fine, and the player software is also fine.

If you're still getting distortions, how do they sound? Digital distortion sound horrible, it's like a screeching sound. (Analog distortion usually sounds like compression before it becomes raspy.)

I'm assuming you don't have any audio outboard gear connected to your Mac Pro audio output(s). Under system preferences I'm also assuming your output selection under 'sound' is what you need it to be.

 

[Tucom]

So the Mac Pro had the logic board replaced and the problem still exists? Two things: Either the replacement logic board has the same problem as the original one, or there's some sort of signal or something interfering with the Mac Pro where it's located when playing back the audio.


Any cell phones near by? Maybe look to see if there's any ground loops or grounding problems where the Mac Pro is plugged in?

 

[DPUser]

Could be as simple as overdriving the headphone amp in the Mac... or severely limited source material that is overdriving the Mac's digital to analog converter.

Is the distortion present regardless of Mac Pro volume?
Does the character of the distortion change when Mac volume is adjusted?

Look for gain adjustments in your software and OS. Many audio programs give you the power to add a lot of gain. Don't push anything above zero.

 

[Macsonic]

Try playing the audio file to a different player to isolate the problem and see if there is still a distortion. If the problem is in the Mac Pro most likely all audio files will have distortion.