iTunes4 messes up dynamic range

[David Crandon]

On several of the big Mac web site (Macintouch and MacFixit), they've
been talking about the decreased sound quality with iTunes4 that was
just released.

What they are all describing seems to be related to a decreased dynamic
range, but as usual, when non-audio people try to describe what they are
hearing it's not making much sense.

I was wondering if any of the techies on this list could take their ears
and instruments and tell us what happened between iTunes3 and iTunes4.

Below are some comments from MacFixit that I copied.

Thanks,

David Crandon

> Muffled Music We continue to track the widespread "muffled music" problem appearing on a broad variety of Macs after updating to iTunes 4. 
> 
> Comparing the sound levels using the graduated volume adjustment on the Equalizer dialog, there is a degradation of some 6-9 db (decibels) in the sound intensity  for many upgraders, which is quite significant. The best way to describe the change in audible perception is that a part of the frequency response has been lowered (perhaps mid-range) thus making the overall sound brighter and lacking in weight. 
> 
> The cause of the issue is as of yet unclear, but may be related to the implementation of a volume limiter (which is intended to reduce blaring and distortion at high sound levels) with a narrow dynamic range. 
> 
> Users with third-party sound cards are not exempt from the bug. One reader with an M-Audio Revolution 7.1 PCI card describes his experience with the problem: 
> 
> "I have an M-Audio Revolution 7.1 card installed in my Dual 1 GHz Power Macintosh G4. The sound card comes with software to change speaker configurations as well as basic input/output levels.  Prior to installing iTunes 4.0, I would generally need to keep the itunes volume slide at about 80 percent to keep the VUs from going into the red and never used the equalizer. Now, I can turn all output levels up full, less the equalizer preamp, without coming anywhere near red." 
> 
> Workarounds for this bug are inconsistent from machine to machine, but here is what has worked for some readers: 
> 
> In the iTunes preferences pane, under the "effects" section, there is an option called "Sound Enhancer." Turning this option off has resulted in an improvement for some users. In fact, some readers report that they are able to turn the Sound Enhancer back on without the muffled effect re-appearing. Likewise, the "Sound Check" 
> 
> Playing the same "muffled" files in QuickTime Player, or another MP3-capable application results in normal, clear audio for most users experiencing this problem.