I have bought quite a few HD albums from HD Tracks, some of which sound superb, some pretty dreadful. The very idea that 24/96 should sound much better than 16/44.1 has puzzled me though. Because our ears can't hear anything over 20k (probably not much over 12k for anyone in their 50's if the truth be known). And all the word length affects is the S/N ratio, nothing more. 16 bit is good enough to achieve around 100dB of S/N with proper noise shaping. i.e. more than good enough already.
So by rights, 24/96 files should sound no better in reality than 16/44.1 But all that logic goes out of the window when you listen to Elton John's Captain Fantastic and the Brown Dirt Cowboy in 24/96 and it sounds so much better than the 16/44.1 version. Maybe the improvement was the 24/96 format? Or maybe the mix? Or just better mastering. Who knows, but it is surely better.
But recently something changed all this.
My office PC broke, so my trusty music server - a Mac Mini - was returned to office duties. That meant it was back to AppleTV1 for music serving. The problem is, AppleTV1 will not play 24/96 tracks without downsampling. So what to do with my HD Tracks?
Being an owner of Pure Music, I decided to use its EXCELLENT sample rate conversion facilities to downsample all my 24/96 material to 24/48. At 24/48 the AppleTV doesn't resample and is bit perfect.
To my enormous pleasure the 24/48 HD Tracks resamples sound IDENTICAL to the original 24/96 versions. I mean IDENTICAL. I reinstalled my Mac Mini to do some A-B comparisons and I am unable to tell the difference between them. I have a pretty decent (if not outstanding) hifi with Benchmark DAC2 feeding Wyred4Sound SX1000 monoblocks and Wilson Benech Arc speakers. So not a Bose Sounddock.
I don't know whether other people could tell the difference. Maybe some people could. But I would strongly wager the VAST majority could not. Maybe even nobody could, in double blind testing.
My next test is to try downsampling to 16/44.1 and comparing again. I would not be surprised if these versions sound identical (to their 24/96 counterparts) as well. We will see.