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I think I've discovered a new listening test method, Please help me validate
2Bdecided
post Mar 7 2011, 10:28
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QUOTE (greynol @ Mar 5 2011, 07:54) *
The more I consider my previous reply the more I am absolutely sure you need to cross-fade the transition!
If you were testing the audibility of inverting the signal, that would pretty much destroy the test. You'd get brief silence cross fading original>inverted, but not original>original, or inverted>inverted.


I think ABX is fine - with the choice of doing a cross fade, an instantaneous-but-glitch-free switch, or a glitchy/stopped transition. The tester should know the pros and cons of each, and the log should report which was used.

Cheers,
David.
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NullC
post Mar 7 2011, 16:53
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QUOTE (2Bdecided @ Mar 4 2011, 07:17) *
I agree it would be nice to have an ABX tool with inaudible switching like this.
However, I don't use ABX like that (I always play from start for each click), so haven't tried advanced ABX to see if it works.


Squishyball does glitchless switching: http://svn.xiph.org/trunk/squishyball/

It's not hidden from the useró you tell it which file to play, but you can flip back and forth without any discontinuity (or, if you like, it can insert silence or a beep in the switch).

I use a patched up version for codec development which can play the difference signal. (Handy when the files are almost identical except for a few pointsó I'll use difference mode to set a loop around a difference then blind A/B as normal)
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googlebot
post Mar 7 2011, 17:15
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Squishyball implements "glitchlessness" by just inserting silence into the transition. This can still add correlated pops. A short cross-fade can deliver much better results. I have implemented a tool for all kind of advanced transitions once. But partly due to the choice of Java it wasn't easily integrable into the existing playback ecosystems. It never found that much interest, so I moved on.

This post has been edited by googlebot: Mar 7 2011, 17:43
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greynol
post Mar 7 2011, 18:27
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QUOTE (2Bdecided @ Mar 7 2011, 01:28) *
If you were testing the audibility of inverting the signal, that would pretty much destroy the test. You'd get brief silence cross fading original>inverted, but not original>original, or inverted>inverted.

If one is trying to invert the signal by mixing an error signal it better be done in 32-bit float.


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2Bdecided
post Mar 7 2011, 20:31
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QUOTE (greynol @ Mar 7 2011, 17:27) *
QUOTE (2Bdecided @ Mar 7 2011, 01:28) *
If you were testing the audibility of inverting the signal, that would pretty much destroy the test. You'd get brief silence cross fading original>inverted, but not original>original, or inverted>inverted.

If one is trying to invert the signal by mixing an error signal it better be done in 32-bit float.
Really? Apart from the fact that digital full scale +ve is one less than digital full scale -ve, inversion is lossless with 16-bit integers.

As for the cross fade - pass!

Cheers,
David.
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greynol
post Mar 7 2011, 20:35
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Simple example:
-0.6 requires summing 1.2 in order to get 0.6.

Is is not clear to everyone that the OP is interested in summing an error signal in order to swap versions?

But you're right though, David, a single method of seamless switching will not always be possible depending on the samples being tested. As I said earlier, if the transition itself poses an audible difference and can be used to determine which is which, clearly we no longer have a blind comparison.

This post has been edited by greynol: Mar 7 2011, 21:22


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NullC
post Mar 7 2011, 21:38
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QUOTE (googlebot @ Mar 7 2011, 08:15) *
Squishyball implements "glitchlessness" by just inserting silence into the transition. This can still add correlated pops. A short cross-fade can deliver much better results. I have implemented a tool for all kind of advanced transitions once. But partly due to the choice of Java it wasn't easily integrable into the existing playback ecosystems. It never found that much interest, so I moved on.


Er. It has three modes:

-B --beep-flip : Mark transitions between samples with a short beep
-M --mark-flip : Mark transitions between samples with a short period of silence
-S --seamless-flip : Do not mark transitions between samples; flip with a seamless crossfade (default)

(of course, these can be switched at runtime too)

The seamless is as it says, its a crossfade using a power complementary window.

I toyed around with nudging the transition point to the position with the least difference but couldn't find any realistic samples where it made a difference.

For ABX the seamless option has the risk of making it possible to distinguish X from A/B based on transition artifacts, so the beep/mark options are probably better there.


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googlebot
post Mar 7 2011, 21:53
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Oh, ok. I only knew -B and -M.
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