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Discussion Starter · #1 · (Edited)


After correcting for a 0.2 dB difference in level, the native 24/96 and SRC versions of the test files are again ready for downloading.

As many of you know, I'm conducting an informal experiment with the AVS community to investigate whether or not true high-resolution audio files—with information beyond what a Redbook CD can accommodate—can be reliably distinguished from the same files that have been downconverted to CD specs. The parameters of the experiment can be found here.

Shortly after I made the audio files available for download, several members reported that one of each pair of files was 0.2 dB lower in level than the other. This was determined to be the result of subjecting a copy of the native 24/96 file to two sample-rate conversions—first down to 16/44.1 and then back up to 24/96—in order to hide the fact that it has a lower resolution. It turns out that the sample-rate conversion software—Sonic Solutions Sonic Process in this case—lowers the level of the file being converted by 0.1 dB to provide some headroom so the calculations will not cause any clipping. (Most sample-rate converters do this, not just Sonic Process.) Because the "hidden" 16/44.1 version went through two conversions, it was 0.2 dB lower in level than the native 24/96 version, which is close enough to the just-noticeable difference (JND) that listeners might pick the native high-res version on that basis.

A number of solutions to this problem were proposed, including a couple of rather complicated, multistep conversion procedures. We also experimented with normalizing both files as well as simply increasing the level of the converted file by 0.2 dB and decreasing the level of the native file by 0.2 dB. In addition, we considered raising the level of the file that would be converted to CD specs by 0.2 dB before doing the conversion, but there wasn't enough headroom in two of the three files to do that without clipping.

In the end, neither Mark Waldrep (aka Dr. AIX), who provided the files, nor I believe that the procedure by which the levels are matched makes much difference for this experiment. Still, I wanted to process the files as little as possible, so I rejected the idea of normalizing all of them. Because I subscribe to the "cutting is better than boosting" school of thought, I decided that the best course of action was to decrease the level of the native 24/96 files by 0.2 dB rather than boost the level of the converted files. Yes, that decreases the dynamic range of the native file, but only by 0.2 dB, which still leaves it beyond what CD can handle in each case. I have checked all three pairs of files using foobar2000's ReplayGain Scan function, and each pair is now within 0.01 dB of each other, well below the JND of perceptibility.

Of course, some AVS members will object to this approach, but I seriously doubt there would be unanimous approval of any solution within the AVS community, so I made an executive decision to do it this way. Those who believe my solution is unreasonable are free to simply not participate and to argue their position in the comments here and in the other related threads; all I ask is that you keep it respectful and not personal. Just keep in mind that this is an informal—and, I hope, fun—exercise that invites AVS members to make their own determination about whether or not the extra information in a bona fide high-res audio file makes a perceptible difference over the same content that conforms to CD specs.

Some members have also suggested that the results of the experiment should not be limited to those with audio systems capable of reproducing the extra information in the native high-res files. It's fine with me if you want to submit your determination of which files are high-res regardless of your system's capabilities, but all submissions must include a complete list of all components used in the test, including makes and models, as well as how they are connected together. I will compile the results separately for those with truly high res-capable systems and those with systems that can reproduce no more than CDs can deliver.

The new audio files are now available by clicking on the links below. As before, we've zipped each file so all browsers will initiate a download rather than trying to play them, and we've combined all six files in a single zipped package. The "A" and "B" assignments are new, so they are labeled "A2" and "B2" to make sure there is no confusion with the previous files. To make the assignments, I used the random-number generator at random.org, which is based on atmospheric noise rather than a pseudo-random algorithm—hence, it is truly random. I set the range from 1 to 100 and let it generate a random number for each pair of files—if the number was odd, the native high-res version became A2; if it was even, the native high-res version became B2.

So let's try this again, shall we? If you have already submitted your determinations, please do so again with these new files, and be sure to include a complete description of your audio system. Remember, this is not an ABX test—simply listen to each pair of files as many times as you wish, at the same volume level for both files, and see if you can tell them apart. And please don't go poking around the files with audio software—just listen. If you can, decide which one is high-res, A2 or B2, and send me your determinations by PM with the subject "AVS AIX HRA Test 2."

Thanks to all who identified the level-difference problem and offered suggestions about how to correct it.

All in one:

AVS/AIX HRA Test Files 2

Individual files:

Mosaic A2
Mosaic B2
Just My Imagination A2
Just My Imagination B2
On The Street Where You Live A2
On The Street Where You Live B2

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downloading now, should be fun!
 

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I recall that in testing my own hearing of music files in the past, using automated ABX software, I could demonstrably perceive 0.2dB as a difference, but not 0.1dB. [I recall that the subjective difference I perceived was not of loudness, simply an extremely small uncharacterised "difference".] So indeed it seems quite important to have corrected the files for comparison to bring them to equal amplitude within a very close tolerance.

As for sample rate conversions causing slight amplitude differences, I have never noticed that with the open source product Audacity [excluding any possible effects from introduced dither].
 

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I could not tell any difference, but my system is not equipped for ultrasonic playback. I will say this, somewhere between 16,000 Hz and 17,000 Hz I lose the ability to hear a sine wave. I can't see how I'd be able to hear any recorded information at frequencies higher than that. just because it was recorded with music—not when an isolated tone is already completely inaudible to me at 20,000 Hz.
 

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As for me through my system, I could not discern any difference.

It would have been interesting to have listened to the same files through a few of the extreme high-end audio systems at the T.H.E. SHOW at Newport Beach this year. Would I have noticed any difference?? Who knows but it would have been fun.



m
 

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As for me through my system, I could not discern any difference.

It would have been interesting to have listened to the same files through a few of the extreme high-end audio systems at the T.H.E. SHOW at Newport Beach this year. Would I have noticed any difference?? Who know but it would have been fun.

m
I can reliably hear the difference on my laptop and headphone. No exotic system is needed. I hope everyone tries the files regardless of what system they have.
 

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I can reliably hear the difference on my laptop and headphone. No exotic system is needed. I hope everyone tries the files regardless of what system they have.
After I read your post, I became intrigued. I asked my wife to sit and listen. She was able to hear a difference in all three through my audio system.

Maybe I should have my ears checked out.
 

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Yes, but nothing you can do about its condition. ;) :D
You might be right but I will keep trying to convince my wife that this will do it for me...

 

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Age and Gender Selective Test!

For those under 30, are of the Female Gender under 60, but definitely not for those from the Construction Industry!

(May also exclude Younger Generation who like to listen with ear buds blasting out 110dB!)
 

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Apologies if this is the wrong thread, but is anyone using Genelec 8260A active monitors for this test? I know they're highly regarded, and the specs ( http://www.genelec.com/products/8260a/ ) state: 26 Hz - 40 kHz (-3 dB).
 

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Interesting test

Heard a difference in the sound-stage presentation but that's about it. Need to try with IEMs and laptop.
 

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I could easily determine the high res version for the Mosaic and On the Street Where You Live files. Just My Imagination was a toss up though and I guessed wrong on that one.

My set up was a Mac Pro Quad-Core Tower, a MusicStreamer II DAC, a Yamaha HTR-5550 receiver and Pioneer SP-B22 speakers.
 

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I could easily determine the high res version for the Mosaic and On the Street Where You Live files. Just My Imagination was a toss up though and I guessed wrong on that one.

My set up was a Mac Pro Quad-Core Tower, a MusicStreamer II DAC, a Yamaha HTR-5550 receiver and Pioneer SP-B22 speakers.
What were your ABX scores like?
 

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No sure what you meant by ABX scores but after I made my determination I opened the files and looked at the Spectrogram to see the difference.

That cut off at 22kHz isn't gradual either which makes me think what is noticeable is more a re-enforcment of the lower harmonics (those that are actually audible) and which is absent in the CD quality file. Like when we add a sub-woofer and experience a fuller overall sound.

High resolution files might actually justify those super tweeters that have been around for some time. I'm looking forward to the new Sony - Core Series bookshelf speakers, that have a frequency response of 53Hz - 50kHz.
 
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