Anybody's sound quality get WORSE when upgrading to Snow Leopard?

Coverto, this happened to me when I did a clean install of Snow Leopard and I felt pretty dumb after I figured out what happened. I realized that my Itunes was a fresh install and there the problem was. When you install Itunes for the first time without having any previous versions there are two settings enabled by default that have a negative impact on the sound in a big way. Go into your Itunes preferences and make sure "Sound Check" and "Sound Enhancer" are both UNCHECKED. Make sure these two features are disabled and it should remove the harshness you are experiencing. This is what happened to me. I hope this is your problem as well. An easy fix.

"Sound Check" and "Sound Enhancer" are already unchecked... I tried fiddling with them, checking them and unchecking them, and am still getting sound that's headache-inducing! I'm wondering whether the output signal of Snow Leopard is too strong for my DAC to handle. At any rate, very curious and grateful for any other thoughts on possible fixes before I have to go find a copy of the old Leopard operating system to reload...

Also - in addition to a clean install of Snow Leopard, I moved all my music files from the internal drive of the MBP to an external drive, which is now feeding it via a wireless connection - I don't suppose that could be a factor here?

Have you tried using the external drive wired to your MBP? Try this to eliminate that variable. Many people have reported a cleaner more forward sound with Snow Leopard, it very well may be revealing more about your setup and showcasing weaknesses in a more "magnified" way, whereas with Leopard that was masked. I went through the same thing when I upgraded and changed my setup a little bit, now it sounds better than it ever has. I still have Leopard 10.5.8 installed on another disk and if I boot into that drive and play music it sounds like a blanket is over my speakers. I won't ever go back because in my opinion that is going backwards in sound. What is your full setup?

David, I just did some more fiddling with iTunes and discovered that for some reason it was reverting to "Sound Check" - at maximum level, no less - repeatedly after I switched it off. That appears to be fixed now, and the sound appears to have smoothed out! It's a little hard to tell definitively, because my ears have been so traumatized from all of this. I just popped a couple of Advil and I'll wait a few hours for the headache to subside then report back!

Also, per your good points, I've got an inexpensive DAC and a consumer-grade receiver coupled with a pair of extremely revealing speakers that I just bought as a cornerstone for a new, high-end system - a pair of Green Mountain Pico Executive HDs. I'm thinking that maybe the budget front end coupled with the high-end speakers is exacerbating this whole issue - although before the Snow Leopard upgrade it had been sounding pretty sweet!

Well, I finally was able to do a little more experimenting tonight and the preliminary indication is that it's the wireless hard drive setup rather than Snow Leopard that's causing the issue. Although I do feel a bit sheepish, this answers a separate question I had about wireless hard drive connections and sound quality that I previously had trouble getting any definitive answers on. So at this point, I suppose I'm wondering if there are any other folks out there who have confronted this problem successfully without resorting to wiring up their external drives? But I suppose that's for another thread.

Thanks again, David, for the input, and apologies for the wild goose chase!

coverto, I'm glad you found your goose! This whole computer audiophile thing seems to be one big goose chase at times, thanks for joining in on the hunt.

Would the Streaming Buffer Size have any effect? Mine is set to Medium (rather than Small or Large).