mystran wrote:Personally I'm not a huge fan of noise-shaping 44.1kHz/48kHz audio anyway (ie. I played around with it at some point and concluded that as far as my ears are concerned it's just waste of time), so I admit I haven't really tried to optimise the dither.
Agreed...not trying to start a fracas, just adding observations...no exhaustive study, just some thoughts through the course of past experiments...
1. Noise-shaped dither sounds crappy on some sources. Don't assume it's always better than TPDF.
2. TPDF dither always sounds fine, as expected.
3. Often (likely, for most multi-instrument songs, single instrument polyphonic songs...er, and even just most instruments), no dither at all sounds just as good as TPDF.
Ground rules for these observations:
I'm talking primarily about 16-bit. (It's silly to talk about dithered 24-bit—if you think otherwise, let's discuss physics—and we rarely use other sizes. If you need 8- or 12-bit, do what you want, I don't care, I'm just talking about formats that most people deal with as an end product.)
I left "golden ears" out of the equation by nulling with the original in the digital domain and adding enough gain to easily savor the quality of the error. The sound of the error is all that matters (the amplitude is a given)—it either sounds bothersome or it doesn't.
Some might submit that #3 is only true when there is sufficient noise already in the recording ("self dither"). Yes, that's often the case, but not what I'm getting at. I found that normal music (even without drums and cymbals) seemed to be chaotic enough, using the cleanest of sources, that the error lacked enough correlation to be perceived as anything other than unmodulated white noise throughout the song—nothing that stood out, even at artificially high levels. (I wanted to test this more, using mixes from big-time pros, but found they get cold feet about having their stuff looked at that closely, even if you promise that no one else will ever know, and the meaning of the test has no implications about the quality of the sources.)
(A reminder for anyone wanting to experiment: Don't fall into the trap of, say, dithering to 8-bit so the error is loud enough to hear easily, and making the assumption that dithering to 16-bit is the same thing, but 48 dB quieter—this is not a linear process, you can only determine the effects for 16-bit by doing 16-bit. Then null and add gain to examine the error qualities.)