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Old 26th February 2011, 09:15 PM   #1
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Default Distortion blind test

Hi guys,

I've started a blind test on distortion over on head-fi that you can do. I would appreciate your feedback as you guys are probably more knowledgeable about this sort of thing.

To sum up things so far. (copy and paste from head-fi)

Here are the files

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I've done something to the files that will shed light on to something that is mentioned a lot but I have never seen any evidence on. I'm not going to tell you what the differences are but it's not compression related or any special effects etc. If you do the test I would like you to PM me which ones you think sound the best, in order too if you can. If you can't tell the difference say that too. Once I get 20 results or so I'll tell you what I've done.

The song is the first 25s of Chan Chan by the Buena Vista Social Club but if someone can suggest a good reference song for this test I can apply the same thing to that song too.

Thanks for your help.

Edit: Added first 35s of Evil Ways by Santana

Edit: Added the songs in zip files

Well I've got about 10 results now and they're fairly consistent so I'll tell you what I did. I have added 5% harmonic distortion in the different harmonics from 2nd to 5th plus there is the original. The general consensus so far in best to worst sounding is

original -> 3rd -> 2nd -> 5th -> 4th

about 25% can't distinguish any difference (I suspect it may be more because I've had a lot more downloads than results) 50% can distinguish only the 4th and 5th and 25% can just distinguish between the rest also.

This is how I did it, please tell me if it was wrong.

Took the original flac I had and upsampled to 24 bit wav.

Imported to matlab and added harmonic distortion by using the Chebyshev n polynomial of the original waveform to create nth order harmonic distortion.

multiplied the by 0.05 and added it to the original wave form.

converted to 24bit flac so I could use replay gain

downsampled to 16 bit wav applying replay gain and dithering.


So far the results seem to indicate that the odd harmonics are favoured to even ones isn't that the opposite of what we're told?
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Old 10th March 2011, 04:47 AM   #2
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I would not necessarily be surprised to learn people favour odd (or high order) harmonic distortion in a short passage such as your test.

Higher orders tend to introduce artifacts that often are interpreted as sounding "cleaner", brighter and/or more detailed by some, especially over the short term. Recording engineers have a vast arsenal, and they use it, to deliberately introduce distortions in music.

So, it's a fallacy to assume everyone naturally gravitates to the lowest order distortion version of a music recording. I would only expect a trained ear to immediately recognize the distortion signature in the files you've created.

Although it would be much harder, I think a better test would be to create two otherwise identical amplifiers with two different feedback loops, and match the gain. In this way you could create two devices that would always add mostly low order or mostly high order harmonic distortion while (hopefully) limiting each to the identical total harmonic distortion figure.

This would give an opportunity to introduce listener fatigue to counteract the preference for artificial detail added by the introduced higher order harmonics.
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Last edited by Johnny2Bad; 10th March 2011 at 04:54 AM.
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Old 10th March 2011, 07:47 AM   #3
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I listened to the first one and said "what happened to the high end' ? Then I pulled out my Santana from a CD and played it and mine is as I expected. So where did you get that copy? I'm not sure how to get you a copy of mine to compare but I think you'd be surprised. Mine was not any special version, just the Columbia Santana's Greatest Hits.

G
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Old 10th March 2011, 08:13 AM   #4
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Quote:
Originally Posted by stratus46 View Post
I listened to the first one and said "what happened to the high end' ? Then I pulled out my Santana from a CD and played it and mine is as I expected. So where did you get that copy? I'm not sure how to get you a copy of mine to compare but I think you'd be surprised. Mine was not any special version, just the Columbia Santana's Greatest Hits.

G
It should be very good it's an MFSL UDCD, Santana - Santana Ultradisc II™ 24 KT Gold CD - Mobile Fidelity Sound Lab, Inc.,

I downloaded it from the net though, (cough), so maybe it's not.

You can email me your version at jagduley at gmail.com if you like.

Cheers,
James

Last edited by porthillsbomber; 10th March 2011 at 08:13 AM. Reason: spelling
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Old 10th March 2011, 09:03 AM   #5
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Extremely clever test! And one that I'd generally encourage except for a major caveat: if this is illegally downloaded and distributed material, anyone participating is at risk, especially in the US. Many record companies are extremely aggressive about copyright enforcement and the penalties are very, very high. I won't touch it, much as I'm curious to give it a spin.
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Old 10th March 2011, 06:33 PM   #6
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Originally Posted by SY View Post
Extremely clever test! And one that I'd generally encourage except for a major caveat: if this is illegally downloaded and distributed material, anyone participating is at risk, especially in the US. Many record companies are extremely aggressive about copyright enforcement and the penalties are very, very high. I won't touch it, much as I'm curious to give it a spin.
Ok I never thought about like that. I could put up stuff that I've ripped from my own CDs but wouldn't you guys still be illegally downloading it?
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Old 10th March 2011, 06:37 PM   #7
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Yeah, the copyright laws are pretty restrictive. If it's a short excerpt from a legally obtained CD, and it's meant for research purposes (which it clearly is), I would guess (but IANAL) that Fair Use would apply.
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Old 10th March 2011, 08:32 PM   #8
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It's not the downloading that gets the record companies legal mavens excited, it's distribution. That's why the favorite victims of record company action are kids and non-computer-savvy people who 'share' their entire music collection to the P2P networks.

So, we're probably OK in downloading the files (downloading is still legal in Canada, not in USA) but the Portshill should check his situation in Oz about the legality of distributing.

I do think the Fair Use thing would apply in any case.

And with millions of illegal downloads every day, this would be a stupid target for action...not that that gives me any reassurance- just look around....
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Old 10th March 2011, 10:13 PM   #9
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Probably the best material for a test like this would be a well recorded solo performer - acoustic guitar and vocals.
No copyright worries either.
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Old 10th March 2011, 11:03 PM   #10
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How about this Masters From Their Day | Home
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