I am a member of several audiophile FB groups and regularly post comments when I think I have something to offer. Recently, someone asked whether high-resolution was really worth it? Several others chimed in taking a variety of positions. But there was one comment from a well known audio expert, that contained a link to an article that he had written about high-resolution audio. He takes the position that it’s unnecessary and that “repeated studies” have shown that listeners cannot tell standard-res from high-res audio. I clicked on the link and read his brief article. I disagree with his conclusions that ultrasonic frequencies have no effect on “in band” frequencies and that 24-bits is virtually identical to 16-bit audio, but that’s not what triggered this post.
To reinforce his position, he prepared a group of four audio files so that readers could compare standard-res vs. high-res for themselves. He got a hold of a couple of “HD recordings” — one a pop tune and the other a classical track — and processed them to standard-res and then placed the down converted file in a 96 kHz bit container. This results in two files that are exactly the same size. Those wishing to participate in his casual survey can listen repeatedly to the files on their own system and then report back what they think are the standard-res versions and which are the high-res versions. So I downloaded the zipped file and set about to make my own comparisons.
Wouldn’t you think that a test of this sort would require that the source recordings actually be high-resolution? The original 96 Khz/24-bit bit files have to “have content out to the upper limit of a 96 kHz sample rate”, which means there would be partials up to the Nyquist frequency of 48 kHz. So the first thing that I did was analyze the files using Adobe Audition. I wanted to confirm that the examples sere worthy of comparing. Well, I wasn’t surprised to discover that there was virtually no difference between the A and B version of the files! Take a look at the spectra of the classical example from the download.
The “so-called” high-resolution track is on the right hand side and the downconverted 44.1 kHz track is on the left. The standard-res version should have a sharp upper limit at around 22 kHz but it shows some phantom ultrasonic stuff. The right hand spectra does extend slightly higher — maybe to 24 kHz but there’s not a lot of ultrasonic material there.
I know what a real high-resolution spectra looks like. There are lots of them in previous posts and lots of them in the Music and Audio book. I have included the spectra of one of my high-res classical tracks below for comparison.
The right half of the spectra shows a huge amount of ultrasonic audio — well past 35 kHz. This is the finale of Stravinsky’s Firebird Suite and is a particularly loud section. The left hand spectra is much quieter and doesn’t actually pass above normal CD frequencies but does have a sharp cutoff at 22 kHz.
A better way to illustrate the amount of content provided by high-res sample rates is to scan the entire file and plot the amplitude vs frequency of the entire selection. The plot below is the classical piece I downloaded. Notice that the standard-res converted file actually contains more ultrasonic content than the original! That’s not supposed to happen. Now maybe this is the result of the software that was used to make the conversion but it definitely shows lots of content above 24 kHz (I converted down to 48 Khz). The red line should drop straight down — and it doesn’t.
Take a look at the conversion that I did on my file. It shows the proper relationship between a real high-resolution track and a CD version. The red line does drop immediately at 22 kHz.
So I wonder what kind of results the author of the comment has received from his survey. It would be absolutely impossible for anyone on the planet to perceive any differences between the two files he provided. I’m not going to claim that listeners would be able to perceive differences between my A and B versions, but at least I know that substantial differences do exist. As I said, I wasn’t surprised that the audio he acquired didn’t measure up. There isn’t a lot of really good high-resolution content available from any label. I’m in a unique position because my entire catalog boasts fidelity greater than vinyl LPs, analog tapes, and CDs. But that’s not the reason I advocate for real high-resolution tracks. There are other “non audible” reasons why the world should adopt 96 kHz/24-bits as the minimum AND the maximum specifications. We’ll talk more about that in Part II.