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In Reply to: Fascinating stuff, thanks for your considered reply, and... posted by Djhymn on March 15, 2005 at 09:16:27:
>Can you briefly explain where the errors can arise in testing? I've long thought that there was an inherent flaw in DBT/ ABX, at least with regard to mindset, or opinion, or lack of either, on the part of the individual running or controlling the test.>All of those things you mention are variables which affect the results of a DBT which is why you need a lot of trials from a lot of people for the results to be statistically meaningful. A Swedish Audio Society DBT which was published a couple of years ago identified differences between two different CD players but found that experienced listeners (disc masterers and recording engineers) could identify the differences where the average audiophile couldn't. But there are more basic issues.
In actual science, no assumption can go untested. DBTs were designed for use in medicine for new drug trials and have been adapted to psychometric testing. In the latter application, a known test tone, noise or distortion artifact is introduced and the subjects are tested to see if they hear it, alone or added to a program, and in many cases these can be identified down to the threshold of hearing.
Since it is used in hearing tests like this, the ABX advocates assume that it is just as valid for comparing two audio components with unknown differences using music - a program which is dynamic and constantly changing. But this assumption has not been tested - i.e. forced choice ABX DBT compared to relaxed blind ABAB listening between two components of known and specified audible differences.
Part of the problem is correlating real audible differences to measurements because it's hit and miss (as you see from Stereophile's valiant atttempts), particularly when the differences are out of the frequency response domain - like imaging, tonal color or dynamic contrasts, for example. How do you creat two identical, say, amplifiers, but give one better dynamic contrasts and change nothing else for the test?
And then there's the theory of how the brain processes information. When you are relaxed, listening to music, your "right brain" (emotional, intuitive) is functioning. In an ABX-type DBT, you can listen to A and then switch to B. You are able to listen to each as long as you want switching back and forth. Now you switch to X. As your audible memory is quickly fading, you are forced to make a decision about whether X is A or B. Your brain switches to the "left side" (rational, logical) for the decision-making and you can no longer remember the differences you heard unless they are large, say about 2dB or greater, so you decide "no difference" and the results are null. DBT advocates scoff at this theory, but it has not been disproven by a validation test.
Most audio ABX DBT results are null. ABX-DBT proponents say most all equipment, except speakers, sound the same. Listen and decide for yourself.
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Follow Ups
- Here's the long version.... - mkuller 11:38:12 03/15/05 (7)
- Nice, thanks! - Djhymn 16:33:33 03/15/05 (0)
- Re: Here's the long version.... - Steve Eddy 12:20:30 03/15/05 (5)
- Is that really the way it works?.... - mkuller 14:58:16 03/15/05 (4)
- Re: Is that really the way it works?.... - David Aiken 16:57:13 03/15/05 (2)
- So there is still a need for a test to validate audio DBTs... - mkuller 10:45:47 03/16/05 (1)
- Not necessarily… - David Aiken 22:31:00 03/16/05 (0)
- Re: Is that really the way it works?.... - Steve Eddy 15:26:18 03/15/05 (0)
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