I have to say the difference between no dither and dither, with or without noise shaping, is quite noticeable. Especially when listening to the "bells" at the start of YYZ. With dithering, they sounded clearer and more open than without dither. The guitars in Limelight sounded better, hard to describe, but definitely better. I could not really hear any difference between dither without noise shaping and with light noise shaping. Dynamics also seemed slightly improved on the dithered tracks.
It can be unhelpful to use noise-shaped dither when you're going to lossy encode the file. The extra high frequency noise can waste bits. (Speeking from a theoretical stand-point, rather than practical experience!).Normal dither, at the correct level, is a good choice.
Next, I WaveGained the files using:- 16 bit, no dither- 16 bit, dither, no noise shaping- 16 bit, dither, light noise shaping...I have to say the difference between no dither and dither, with or without noise shaping, is quite noticeable.
But, I noticed a strange thing when I checked the file sizes of all the test tracks; the 3 versions of each track were identical in size after encoding in AAC. Strange, I had expected to have some variation in file size.