Is it possible to 'denormailze' an audio file?

Normalization is just a volume change.
 
But I think you're really talking about the ridiculously overzealous compression/limiting that's become common in recent years and there's no good way to reverse that.

bruckner2
these days CDs are maxed out with very low dynamic range. Is there a way in sound Forge 10 or Sonar to restore these files to their 'non-blasting loud' original form?

As already stated, that's not normalizing - that is brickwall limiting. Once that is in place I don't believe there is any logical way to remove it.
 
I find that Commercial CD's aren't nearly as bad as the same songs available through online music services - even iTunes. I'm not sure if the mastering engineer is providing different "loudness" levels to different mediums, or if certain music services compress even further - but quite often they are ridiculously over done. I find it similar to the treatment that FM radio adds in an attempt to get a loudness edge over their competitors.

Kamikaze

davdud101
like decompression?

 
That's expansion isn't it. I'm not saying it possible, just referring to the terminology

Actually a little more complicated - both compression and expansion can be either upward or downward.
 
The overwhelming amount of the time when compression is used it's downward compression, which means stuff above the threshold is turned down. 
 
Upward compression is rare, but there are a few plugs that do it - it means stuff below the threshold is turned up. It's effect is somewhat similar to, but not quite the same as parallel compression - it turns up the quiet stuff like room sound and noise but leaves the top of the signal alone. The noise issue is likely why it's so rarely used.
 
 
Similarly, expansion is also usually downward, meaning stuff below the threshold is turned down. The much rarer upward expansion means stuff above the threshold is turned up.
 
In theory, one could try upward expansion to counter downward compression. But the problem, as others have stated, is that the processor has no way of knowing what part of the signal was compressed and exactly how and how much it was compressed.

The short answer is NO.   Once you put the compression on something and apply it.... saving that file with the effects.... nope.... it's printed.  Using software to try to guess what it was like before the compression likely will not give you good results.