Originally Posted by xnor
I'm still not convinced because for example if you play the recording at a 20 dB lower level you want a 20 dB difference loudness correction curve (as described above) regardless of the recording's level. For example, when there are silent (e.g. 30 dB softer) passages you don't want a 50 dB difference loudness correction curve.
Playing a recording 20dB lower doesn't result in a 20dB difference in the correction, even at the extremes. Studying the curves, if you assume a reference at 85dB SPL mid-band, then drop 20dB, the correction at 20Hz is about 10dB, and progressively less as you move to the mid band. The correct never comes close to 50dB at any practical listening volume level, in fact, probably maxes at 20dB at 20Hz at 40dB SPL mid-band re: mix reference. Now, 20dB is not small, but considering that play level is skewed 45dB from mix level, and averaging at 40dB SPL, and the correction lets you hear the entire mix spectrally balanced, it's a significant advantage.
But no amount of discussion of the principles will ever beat just listening. If you have an iOS device, try the Songza app for free, or spend a buck on "amp". All in all, very little lost if things don't go well. But if you do like what you hear, you've found a great app, and may actually want to try the same processing in your AVR some day. The audition would be to listen at a reference level, like around 80dB SPL or so, then with Dynamic EQ on, drop the play level 20dB or so and listen for spectral balance. Then, without touching the volume, turn the processing off. You'll get the idea pretty quickly.
Personally, the only reason I don't use it all the time is my favorite player is a 160gig iPod with my entire library on it, and "amp" won't run on an iPod. So to use "amp" I have to load up a selection of tracks to my iPhone or iPad, and listen to that little library with "amp".
I'm not a big fan of Songza, I guess I'm too old.