[miceblue]

Hypothesis: If HD music sampling rates (> 48 kHz) make a difference in audio quality, then downsampling HD music with signals above maximum frequency obtained from the Nyquist frequency defined by the Red Book standard (22.05 kHz) would degrade the audio quality because the natural ultrasonic frequencies that only HD sampling rates could capture would be eliminated.

The problem with that theory is that tests by the AES indicate that frequencies outside the range of 16/44.1 recording add absolutely nothing to the perception of sound quality of music. If we can't hear them, they don't matter to anyone but bats.

However a high sampling rate can wreak havoc in some home audio components that aren't designed to deal with super audible frequencies, creating artifacting and distortion down in the audible spectrum. In these cases, having the super audible frequencies in the recording makes it poorer quality, not better.

So basically, it's a no win situation. If the inaudible frequencies are there, it can only hurt the sound quality. It can't improve it.

Yes, but the AES papers don't analyze the music in a spectrogram before testing, or if they did, none of the papers I have seen do so. For all we know, there could be zero ultrasonic frequencies to begin with, so higher sampling rates would be absolutely useless with regard to my hypothesis. I specifically did a test on that song exactly because it has natural ultrasonic frequencies from cymbal hits. Some percussion music, such as gamelan, are very well-known to naturally produce ultrasonic frequencies. There are a few published papers about this, and likewise for ultrasonic content being able to be detected by humans. I don't believe any of the AES papers specifically target this music, where higher sampling rates would capture those signals. Instead, most of the papers I've seen just use a DVD-A, or the SACD, and that adds an additional source of error, as in the transport, not to mention the unknown variable of how the audio was mastered for those formats.

As for playback, yes you are correct about home audio components not being designed to handle supersonic frequencies.

This paper suggests recording in HD formats produces sound that is more like the live recording, but playback on loudspeakers with ultrasonic frequencies is harmful to that.
http://www.aes.org/e-lib/browse.cfm?elib=13967

The papers published from AES, although they're scientific papers, they don't list their impact factor. Thus, I often don't take these papers very seriously since I don't know how useful it is to the scientific community.


On the other hand, that paper used speakers with supertweeters, which are not used in headphone assemblies (to my knowledge). The HiFiMAN HE-560, although a useless value without standard deviations, is rated to produce sounds up to 50 kHz. I'm assuming any decent headphone amplifier can handle ultrasonic frequencies with linearity as Tyll measured from Innerfidelity. Keep in mind that the maximum signal from a 96 kHz sampling rate is 48 kHz. Many amplifiers measured there showed a linear frequency response from that frequency area.

 

[bigshot]

The one I saw back when there was no paywall was about ultrasonic frequencies, not just sampling rate. It specifically tested music with super audible frequencies. These frequencies are far beyond human's ability to discern musical pitch, so if they can be detected at all, it's as sound pressure, not music, not even really sound.

 

[castleofargh]

hypotheses:
1/ unless you're a kid, you usually don't even hear 20khz so above that is a joke. it's admitted by any doctors and it's pretty easy to test your own limit at normal listening levels with test tones.
 
2/ controls tests trying to show if we perceived the ultrasounds in music, all showed that ultrasound didn't play a part and that at best we could physically sense ultrasounds but only at levels well above what we get while listening to a record. the only paper I saw telling otherwise was about a team who's trial could never be reproduced after, and the conclusion was the IMD from the ultrasonics came back into the audible range because of the gears used for the test.
 
3/ controlled tests trying to show if we perceived a difference between CD and higher resolutions showed no difference and here again those who showed differences were not blind tests, the masters were different, or the files were altered in a way that was more than a simple change of resolution, making the all test dubious at best(last test I've seen was like that).
 
from those information, my own conclusion is that if someone perceives clear audible differences between resolutions, then:
-maybe he dreamed those differences?
-maybe the file conversion didn't go as smoothly as it should have?
-maybe the masters weren't the same?
-maybe his sound system is responsible for the sound differences? if he used 2 different resolutions for the test instead of putting both files in a common format(like listening to original SACD file and then to original CD file). apparently the most common reasons in this case being IMD from the ultrasonic sounds appearing in the audible range(so CD version is actually better), or the high freqs being slightly rolled off by the low pass filter(something that shouldn't happen on most modern DACs as the DAC would oversample anyway for a better filter).
 
so mainly I would say different masters or failed conversion.
 
but I really can't find a reasonable explanation for audible superiority of higher res. theoretical why not, measurable often yes, sometimes it's worst depending on audio system. but audible because of the type of file or resolution...
 
 
 
 
now about the hifiman going up to 50khz, you should look at this kind of values with big skepticism. what does the given range means? that it's in a +3/-3db variation from 15hz to 50khz? that there is "something" at 50khz even if it's 130db below the same 1khz signal? what about distortion in the ultrasonic range? sony also like to boast with unrealistic frequency ranges for even the crappiest IEMs giving some 30khz max when I can hardly get anything past 13khz(my own ears stop at 17khz or is it the limit of my best headphone?). almost 100% of headphone have specs that show 20hz-20khz when almost all of them are badly rolled of on both ends, so I wouldn't care much for brands talking about even more than 20khz.