1101:
Many many years back , the BBC did double blind tests and found that slightly DEGRADING the sound quality gave a seemingly perceived improvement .
I did a double blind test (I think there's an page on US NPR which randomises the order of sample tracks on each page refresh). On a couple of tracks I repeatedly chose the 128mbps Mp3 as best over 256mbps mp3 and lossless flac or wav.
The DAC (external sound card) I've got reads/decodes DSD format, I've d/l music files sampled at double SACD rate (IIRC). The 44k / 16 bit PCM flac version of the file is about 48MB. The DSD file is 765MB. I still can't hear a difference - though to be fair I've got no way of randomly/blind switching.
I believe Amar Bose showed that in controlled tests, humans can't tell the difference between a square wave and sine wave at > 8khz. Great news - but then he went and made Bose 901s and other similarly horrible stuff.