Poor audio quality though Mac Pro

[SnagCleaver]

Are there any known issues (and if so, fixes) with the Mac Pro audio output?

I have iTunes 7.6.2 on a (late '07) Mac Pro (OS X 10.4.10) with JBL Creature II speakers. Nothing too high-end, but enough to expect consistent sound reproduction in a small office space.

Recently I've been experiencing some distortion and poor quality audio. I've tried switching the speaker connection from direct line out to USB via Griffin iMic, and reconfigured the MIDI settings, but still find that tracks which used to play fine (both on this machine and prior to that using same speaker set-up from a PowerBook G4) are sounding like somebody is messing with radio reception (while underwater!) - static interference, uneven volume, distorted frequencies etc. It's a little better with Soundcheck on but still noticable and annoying.

It seems the speakers are fine because I don't get the same problems if I connect them directly to an iPod. The same iTunes libray still plays ok through other machines.

Same issues when listening though headphones.

I also tried re-importing my library from a back-up I have on a remote HD but get the same result.

Seems to occur on various file types (MPEG, WAV, AAC) from various sources, imported CD, iTunes store purchases, downloads, converted vinyl, and age of the files doesn't seem to have any bearing on quality - files which have been in the library for a month are just as suspect as those which were imported by our old iMac back in the '90s, etc.


Any advice appreciated
Snag

 

[Mackilroy]

I also have JBL Creature IIs hooked up to my Mac Pro, but I get consistent audio quality. Is the audio cable running from your subwoofer to the Mac Pro in good condition?

 

[Julien]

I use S/PDIF and it works just like S/PDIF should. Not sure about the quality of the analog outs but computes sound cards (or chip sets) in general have cheep analog circuitry (except for cards from companies like M-Audio).

 

[smirk]

This is a long shot, but are there any high-priority processes sucking up all the CPU or thrashing the hard drive? I have a very old G3 Mac, and when it plays music under load the music stutters.

 

[SnagCleaver]

I also have JBL Creature IIs hooked up to my Mac Pro, but I get consistent audio quality. Is the audio cable running from your subwoofer to the Mac Pro in good condition?

The speakers and cabling seem to be fine as they operate ok when connected to other components (iPod, discman etc).

And headphones (I have a decent Senheiser set) also deliver poor quality from the Mac Pro, but are fone from other devices.

 

[SnagCleaver]

This is a long shot, but are there any high-priority processes sucking up all the CPU or thrashing the hard drive? I have a very old G3 Mac, and when it plays music under load the music stutters.

I generally run a few DTP apps but the problems manifest even when iTunes is the only thing running.

 

[SnagCleaver]

I use S/PDIF and it works just like S/PDIF should. Not sure about the quality of the analog outs but computes sound cards (or chip sets) in general have cheep analog circuitry (except for cards from companies like M-Audio).

Sorry Julien, you've lost me. Even though I spend my day using the thing, computing isn't really my first language .

Can you explain S/PDIF for me. I'm assuming it's some kind of plug-in or something? Am I looking at opening the side panel or anything scary like that ?

 

[smirk]

S/PDIF is just a way of transferring digital audio. For example, I have a fiber optic S/PDIF cable going from my DVD player to my receiver to transfer sound from the DVD to my home theater setup. Digital audio should be higher quality than analog audio (analog is what any standard computer speaker or headphone would use).

http://www.pcmag.com/encyclopedia_term/0,2542,t=SPDIF&i=50760,00.asp

Your Mac Pro has both digital and analog audio ports on it, so I think the other poster was saying that he uses digital and it sounds fine. But analog should sound fine, too.

If you've adjusted the Mac's overall volume via the Sound control panel so it's not too high, and you get this distortion even when using USB audio, and you get the distortion when listening to music through applications other than iTunes (Quicktime Player, maybe Cog.app or Play.app), then I can't think of what it could be. The USB audio rules out a hardware problem, and multiple music players rules out software (as long as they're not all using Quicktime to decode the audio).

Make sure the problems occur in other sound-producing applications. If they don't, try turning off iTunes' Sound Enhancer if it's not already, and make sure iTunes' equalizer isn't set crazy and that the EQ's pre-amp slider isn't way up. This is really mysterious.

 

[SnagCleaver]

S/PDIF is just a way of transferring digital audio. For example, I have a fiber optic S/PDIF cable going from my DVD player to my receiver to transfer sound from the DVD to my home theater setup. Digital audio should be higher quality than analog audio (analog is what any standard computer speaker or headphone would use).

http://www.pcmag.com/encyclopedia_term/0,2542,t=SPDIF&i=50760,00.asp

Your Mac Pro has both digital and analog audio ports on it, so I think the other poster was saying that he uses digital and it sounds fine. But analog should sound fine, too.

If you've adjusted the Mac's overall volume via the Sound control panel so it's not too high, and you get this distortion even when using USB audio, and you get the distortion when listening to music through applications other than iTunes (Quicktime Player, maybe Cog.app or Play.app), then I can't think of what it could be. The USB audio rules out a hardware problem, and multiple music players rules out software (as long as they're not all using Quicktime to decode the audio).

Make sure the problems occur in other sound-producing applications. If they don't, try turning off iTunes' Sound Enhancer if it's not already, and make sure iTunes' equalizer isn't set crazy and that the EQ's pre-amp slider isn't way up. This is really mysterious.

Thanks smirk. I've tried all the various analog options and other players/devices, and adjusting the settings in iTunes prefs/EQ as well as MIDI audio and the System Prefs>Sound. This is why I'm worried that it's something in the MacPro rather than the apps.

Unfortunately my IT guy works out of Prague and I'm in Sydney so he can't just come around and bang on the casing to fix it! And since technically it's my company's machine, I'm reluctant to start poking about looking for dodgy audio chipsets (if there is such a thing in there anyway?).

Might try to get the digital out hooked up and see how it goes...

 

[smirk]

Hmm. Well, if I understood you correctly, you have gotten the same distortion when using a USB audio card, right? So you plugged some sort of audio device into a USB port and then plugged your speakers into that device. If so, then that eliminates any bad audio circuitry or chips on your Mac.

So what does that leave, software? A bad OS component? What happens if you start up the Mac in Safe Mode (boot up the Mac while holding down the shift key)? I'm not sure if iTunes will run in that mode but maybe another audio app will. You probably don't want to reinstall OS X, but (and this is another long shot) you could always try creating a new user account, logging into that account and trying it from there. People sometimes try that when trying to eliminate corrupt preferences from the equation. Other than that, I don't know what to suggest.

 

[SCSnare]

I know this is sort of obvious, but make sure that you don't have any volume settings that are above 0db. One place I'd check is iTunes and if you have any EQ settings active, make sure the Preamp isn't set too high. Just check everywhere you can set the level of the audio along the signal path and make sure it's not set too high.

 

[rockinrocker]

hmmm, sounds like you've got your self a dilly of a pickle.

sounds like you've tried all the standard trouble shooting stuff.

safe mode/ different user are good things to try. i guess the next step would be to run the hardware test and see if that comes up with anything....

(it's on your install disc if you haven't used it)