Well I can't speak to what is done in actual firmware in specific gear, nor in third-party commercial or free software packages (I guess I could read the code for those packages in the public domain; I haven't) but I do know my math. Exact decimation is much easier than interpolation, since you know the exact readings at the to-be-converted-to-sample points. Zero error. No filter at all. Again, this is on paper. I don't know what is actually done, but I know what I can do. With time-aligned signals.
You may be right in common practice, indeed, but that doesn't stop me from doing my own exact sub-sample.
When I go from 96 to 48 I am degrading the signal exactly as much as I have to, no more. And --- again the math is simple -- to go from 44.1 to 48 you have a choice, and my way -- 44.1 to 96 then decimate -- may in fact be better than someone else's direct interpolation from 44.1 to 48. Indeed there must be one filter involved. This is a kind of oversampling, really it is -- I didn't mean to imply it is like Wadia's or others that go way way up. You have a good point though -- I should really go from 44.1 to some HUGE multiple of 48, then decimate. That's better on paper.
I assume the Wolfson DACs are best at 48. I don't know this. All guess work. But I do know that lots of people react (yes, I realize this is not rigorous DBT, but still sample-size-one biased experiments when replicated do tell us something, contrary to popular opinion in the Sound Science forum, and I really do know what I am talking about when it comesto statistics, trust me, I won the Journal of American Statistical Assoication's Theory and Methods award ... alas, a long time ago, but I haven't lost much ... the memory is the second thing to go .. I hope) quite remarkably to these tracks on my iMod + iCube.
Having said that, I really should do a blind test. The same track, from a redbook CD, also available on a DVD-A version, where the liner notes indicate it really is hi res. Then give people 4 tracks:
- 44.1 ALAC (redbook)
- 48 ALAC via 44.1 to 96 to 48 (redbook)
- 48 ALAC via 96 tp 48 (DVD-A) -- the two-track version (when there is one on the DVD-A)
- 48 ALAC via 96 to 48 (DVD-A) -- the 5.1 version from the DVD-A mixed down by me to two-track
In my non-rigorous tests I observe that people order these 4 > 2 > 3 > 1.
I would have thought 4 > 3 > 2 > 1 ... but it seems a lot of the 2-track mixdowns on DVD-A's were rush jobs. Honestly the 2, 3 order probablyy varies a lot. I know a lot of people say that even 96 is a joke, and would expect all 4 of these to be the same ... maybe the mastering is better on the DVD-A's who knows.
All I know is that with Wolfson and 5.5 Gen iPods converted to iMods by Vinnie, and a good amp, I am happiest with the DVD-A 96 5.1 downmixed and downsampled by me, then next happiest with 44.1 converted my way to 48, not directly. Over and over. I'm not hurting anyone, I am not denying global warming, so I plan to continue.
Edited by wavoman - 9/8/12 at 11:07am