The HD-Audio Challenge II

[David A]

 Are my ears up to it? Probably not. 

Hi res music has the technical capacity to produce frequencies above red book CD quality, which is about 22 kHz. That's the one and only difference between CD and Hi res. Anything above 20 kHz or so is beyond the scope of human hearing so to answer your question; nope, and neither are anyone else's.

Frequencies above 22.1 kHz are not the only difference between high res music and the red book standard. There's a higher bit rate as well, which translates into more discrete steps between peak volume at 0 dB and whatever the bottom of the dynamic range is set to.  

There's another possible difference and that is that the high res file is often the result of a separate mastering process, it isn't simply an upscaling of the CD quality data, and there is some evidence that they are sometimes mastered differently, with more attention being paid to producing a better quality master for the high res file on the assumption that anyone paying the extra for the high res file is interested in a better quality result.

I've just been rereading Floyd Toole's "Sound Reproduction" and he gives a passing mention to high res music vs CD quality. He makes the point that most people can't hear above 15 kHz (loss of high frequency hearing starts very early and many in their early 20's are no longer capable of hearing 20 kHz) and he completely dismisses the idea that anyone can hear the higher frequencies that may be present in a high res recording but he does say that there is evidence that people can distinguish between high res files and CD quality and suggest that it is probably due to differences in mastering. It's hard to argue that mastering differences aren't audible when there's a mountain of evidence that people routinely notice differences between remastered versions of the same recording in both CD format and on LP, and in both cases there's no difference in resolution. Mastering differences can and do make audible differences that have nothing to do with frequency bandwidth.

Basically, if the high resolution version is the result of a separate mastering process to the CD quality with greater care and attention being given to things like dynamic range and compression, then there could quite easily be audible differences between the versions. If, on the other hand, both versions come from the same master and especially if one version is simply a rescaling of the other, it's unlikely that there could be an audible difference. On my reading of the details of this test, the CD quality version was a simple rescale of the 96 kHz version, not the result of a separate mastering process in the studio, therefore there shouldn't be an audible difference and the results of this test say nothing about whether high res versions offer better sound quality than CD quality versions of the same music. If you want to test for that then you would need to compare the high res version with the CD quality release because that's the only way of hearing the result of any differences in mastering should the 2 versions have been mastered separately.