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Topic: Dire Straits ABX test (Read 4179 times) previous topic - next topic
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Dire Straits ABX test

I've always thought the 80s original CD issue of "Brothers In Arms" was a spectacular recording.  I used it for years to demonstrate my stereo and still value it as a reference recording.  But I strongly wondered how good my lossy rips were, compared to the CD.    This also seemed like a good time to check my ears.  So I ripped several tracks from the disc at 128k, 192k, and 256K VBR AAC with iTunes.  Going right to the point, here is my ABX of the 128k rip of "So Far Away" against the CD track:

ABX log
ABC/HR for Java, Version 0.5b
March 15, 2009 3:02:17 PM

Sample A: 1_So_Far_Away.wav
Sample B: 1_So_Far_Away(128).wav

Playback Range: 00.708 to 01:24.752
    2:37:20 PM f 0/1 pval = 1.0
Playback Range: 25.514 to 01:24.752
    2:39:19 PM p 1/2 pval = 0.75
Playback Range: 01:27.883 to 03:14.549
    2:41:42 PM p 2/3 pval = 0.5
Playback Range: 04:20.461 to 05:12.200
    2:43:05 PM p 3/4 pval = 0.312
Playback Range: 04:38.180 to 05:12.200
    2:46:01 PM f 3/5 pval = 0.5
Playback Range: 02:13.951 to 04:19.044
    2:47:44 PM f 3/6 pval = 0.656
Playback Range: 03:15.612 to 04:19.044
    2:49:59 PM p 4/7 pval = 0.5
Playback Range: 01:09.456 to 04:19.044
    2:52:15 PM p 5/8 pval = 0.363
Playback Range: 01:36.743 to 04:19.044
    2:54:24 PM p 6/9 pval = 0.253
Playback Range: 02:46.908 to 04:19.044
    2:55:52 PM p 7/10 pval = 0.171
Playback Range: 04:39.597 to 05:12.200
    2:58:30 PM p 8/11 pval = 0.113
Playback Range: 00.354 to 36.854
    2:59:58 PM p 9/12 pval = 0.072
    3:01:56 PM p 10/13 pval = 0.046

---------
Total: 10 out of 13, p = 0.046

Incidentally, I couldn't get ABC/HR to play the AAC tracks directly, even though FAAD would decode them with no problem.  It must be a Mac issue, but I haven't been able to resolve it.  I ended up just using FAAD to convert them to WAV for the test.  Comments?

It was HARD to do this test; I'm not even sure I need to go to the 192k track, but I probably will just for completeness, as I hope to test a couple of other tracks from the CD too and the comparison will be useful to me.  The differences were almost impossible to describe; I finally focused on cymbals and bass, because I really failed badly with the vocals and guitar parts.  Even then, only the ABX results convinced me I was really hearing the differences, because they weren't blatant.  If pressed, I'd describe them as less "smearing" and more detail with the CD track.  The rip sounded very good, though.  I wonder what the percentage of distortion is with the 128k rip vs. the original?  Is there a sensible way to calculate this?

And, what do the rest of you think about this CD for the test?  Any particularly revealing tracks you would recommend?  I intend this to be an ongoing project, though I won't belabor the forum with details unless I come up with some spectacular results.

Dire Straits ABX test

Reply #1
Please correct me if I'm wrong, but maybe if you tried an ABX test with a poor recording, like any Muse album, or the new Metallica, it would be easier to tell the difference.

Dire Straits ABX test

Reply #2
That depends entirely on the nature of the distortion.

ABX test results are only generally valid if the number of trials is fixed beforehand. Running the test until you get under 0.05 skews the results.

It's really common to not be able to ABX anything much beyond 128k. You'll likely only do better with training for specific artifacts, specifically pre-echo and stereo imaging.

Dire Straits ABX test

Reply #3
Is your release pre-emphasized and if so did you do de-emphasis on it?  If not, the upper frequencies will be about +10dB too hot.  Probably wouldn't change ABX results but would make it pretty bright sounding.  I've used SoX to apply de-emphasis to my copy.
Was that a 1 or a 0?

Dire Straits ABX test

Reply #4
Is your release pre-emphasized and if so did you do de-emphasis on it?  If not, the upper frequencies will be about +10dB too hot.  Probably wouldn't change ABX results but would make it pretty bright sounding.  I've used SoX to apply de-emphasis to my copy.


Not sure how to tell.  iTunes doesn't seem to see it, and of course copying the file directly from the CD just treats it as a raw AIFF file.  Is there an OS X app that will let me look at the flags on CD data?

edit: apparently iTunes compensates for the pre-emphasis automatically when ripping?  So I should be OK in that regard.  Neither the AIFF/WAV nor the ripped encode has a different high end balance from what I hear in my CD player...  Surely I'd notice a 10dB rise. 

Dire Straits ABX test

Reply #5
edit: apparently iTunes compensates for the pre-emphasis automatically when ripping?


Correct, iTunes applies a deemphasis filter when playing back or ripping a CD which was mastered with preemphasis.

 
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