Diagnosing Distortion in PC Based System

I am experimenting with a new desktop system:

* iTunes, Apple Lossless, and WAV ripped through iTunes
* WAV files ripped from EAC and Foobar
* Sony Vaio laptop with Windows XP
* Cheapo USB interface by Creative Labs
* Optical output to Behringer Ultracurve Pro 2496
* Also, RCA output to Musical Fidelity tube buffer
* Balanced output to 2 Behringer amps, bridged as monoblocks
* ATC SCM 7 monitors in "nearfield" configuration

At first, I was really thrilled with this little system and stayed up late into the night listening and having fun with both music and movies.

After a weeks break, however, I tried it out last night with less success.

Although the mid bass and midrange are still warm and surprisingly full, and the treble on the ATCs is mostly smooth and non fatiguing, I noticed a very audible, very brittle distortion somewhere in the treble.

This distortion was was particuarly noticeable on piano attack. As the ATCs are supposed to be unusually adept at piano, this was disappointing and quickly become very irritating.

At $199 each, I shouldn't expect miracles from the amps, but they are claimed to have low distortion and with 500 watts each while operating as monoblocks, I can't imagine I am hearing clipping?

The EQ, although also bargain priced, has been praised and claimed as quiet by other users on Audiogon.

Is is possible this could relate to the Apple WAV rips vs the EAC WAV rips?

And God forbid my Chinese amps damaged my tweeters as someone suggested in another thread? (Have not been cranking heavy metal on them or anything.)

How would you diagnose and isolate this distortion, without schlepping my Levinson amp on top of my desk and rewiring everything?

Thanks for any thoughts.
Don't have any idea if you're having the same problem I once had with iTunes but it sounds similar.

Here's a link to my original thread describing the problem and the fix recommended by Jayboard, deleting a corrupted iTunes equalization file. The problem hasn't returned and I was assuming it was because of upgrades to the iTunes software but it's worth a shot since the recommended fix is cheap and painless.
I'd check the speaker with the same source music (CD) on another system and then work your way backwards to the source of the problem by adding components (eventually replacing the CD player source with your PC if all the other components check out).

Thank you - the evil of iTunes is revealing itself to me...

I have just listened to a few tracks ripped in EAC and played back through Foobar and they sound great.

I thought I was fishing for answers with iTunes vs Foobar, but never would have really believed that iTunes or Apple lossless or in particular WAV files ripped through iTunes might be the culprit here.

Which of course makes all the debate on MP3 vs WAV vs Apple Lossless seem even more ridiculous.

Do you think a lot of Apple employees invent usernames for Audiogon?

I am going to stop using iTunes completely, and will also report back on other developments.
I found distortion came through at times on my Sony VAIO using XP when the enhancements were activated and EQ selected. It didn't happen all the time but it was noticeable when it did.
I didn't mean my offer of a suggested fix as an indictment of iTunes. I think it's one of the best, most useful applications ever written. There isn't an application out there that doesn't have peculiarities that you have to learn about and deal with, whether it's iTunes or Oracle.
I have not noticed problems with iTunes. In fact the conversion of Apple ITunes lossy files to a CD Redbook produces remarkably good sound.

Thanks - yes, I realized you were not condemning iTunes.

I love the interface, too, and find it very useful.

But the propietary compression irritates me, and I am not yet convinced it ever sounds as good as WAV and Foobar.

In the meantime, two things have helped:

* I replaced cheap Monster Cable with Signal Cable biwires. The chunkier spade lugs and cables seem to have made a huge improvement.

* It seems the input gain was set too high on the Behringer EQ. Toning this down has helped too.

All in all, an impressive little system which makes working and web surfing much more enjoyable.
Cwlondon, I agree that any compression scheme is a compromise of convenience over fidelity and Apple's proprietary compression scheme has more to do with Apple's profit than with the stated goal of maintaining digital property rights.

However, there's no requirement with iTunes that you use any form of compression or Apple's format. It will import standard WAV or AIFF files just as easily.
Hi Sfar

Yes, I have also experimented with WAV files in iTunes and again, I do confess I love the interface and browsing around.

Somehow I have more confidence in my EAC "rips" to WAV however.