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An ABX is not required.

Posted by Pat D (A) on January 9, 2007 at 14:07:33

In Reply to: Why Is An ABX Box Required? A Proposed Solution! posted by thetubeguy1954 on January 8, 2007 at 13:30:39:

TG54
"This is an honest question, so hopefully someone who's a proponent will take the time to explain why this is so, but first a "brief" explination of why it's being asked. It seems that everytime the the subject of DBTs is raised the proponents of DBTs demand that an ABX be added or else in their opinion it's not a valid DBT!"

MY COMMENTS
An ABX box is not required to do a DBT. Neither is fast switching, although fast switching increases the sensitivity of the test.

The ABX box provides a convenient way to do fast switching.
It also provides a convenient way to set the levels so that they are matched closely enough not to affect the outcome of the test.

It also can randomly pick what the unknown X of each trial is and record it and the answer chosen by the participant. So, one can do a double blind test without needing a third party--unless to witness that the procedures were carried out correctly. The participant can listen to A and B as many times and as long as desired before saying which he/she thinks X is.

(Parenthetically, the audiophile bias to decide that two things sound different [illustrated in the Stereophile amp DBT] would have no affect since one cannot choose "different" but only A or B.)

TG54
"My question is this: Why would using a person whose both unseen and unaware of why he's switching the wires manuelly, be any less of a valid form of a DBT?"

MY COMMENTS
It would be a DBT, only it would be less sensitive than one done with fast switching times between the alternatives. Richard Greene has done SBTs of interconnects with someone manually switching them, as I understand it.

TG54
"I believe if the proponents of DBTs were to accept this method of performing the tests it would alienate a lot less of the opponents of DBTs who object to the insertion of an ABX box and a second set of interconnects! In addition it would strengthen the DBT's proponents arguement that the validity of DBTs have been proven via it's many trials in the medical field. For it would make audio DBTs more like medical DBTs."

MY COMMENT
Actually, this has been tried. In the June 1998 issue of Stereo Review, as I recall, there is a report of just such a slow, manually switched DBT. I don't want to reopen discussion on that article but you can look it up if you want.

A CDP with an analog and a digital output was switched between two systems, one with good but not prestigious components fed from the analog output of the CDP, and one more expensive and prestigious with a DAC fed from the digital output of the CDP. At the other end, the cheaper system had inexpensive wires of rather different lengths, whereas the more prestigious system had expensive speaker cables, not to mention interconnects. The speakers were PSB Stratus Minis.

Level matching was done solely by adusting the controls of the preamp for the cheaper system. IOW, the cheaper system was adjusted to match the more expensive one.

In order to switch between them, the test administrator had to unhook the CDP and speakers from the one system and attach them to the other system, which took less than a minute.

No one was able to achieve a statistically significant result in this test.

Now, what about the controversy? Did it is satisfy those inclined toward subjectivist views? No sirree!! They didn't like the speakers, they weren't sure about the CDP, etc.

Did it satisfy those who like to see DBTs before pronouncng on audible differences? No sirree! While it was valid under the conditions of the test, it would have been more sensitive with fast switching--a few milliseconds at most.

So, past experience does not indicate the controversy would go away or become less acrimonious.

TG54
As it stands there's no equivalent of adding an ABX box and a second set of interconnects in medicial DBTs, like there is in audio. From my admittedly limited understanding of medical DBTs. I believe in medical DBTs adding 2 substances of unknown inertness (which would be like adding the ABX box and the additional interconnects and their unkown additional "inertness" i.e., the addition of their sonic attributes or lack of them) would automatically invalidate the medical DBT in and of itself!"

MY COMMENT
This adds some detail to your concern about the insertion of a switcher and interconnects (or speaker cables) besides the DUTs (devices under test). Well, the switch can be tested and the extra wires can be tested, also, if desired.

TG54
"I could be wrong, but acceptance of manuel switching by an unseen person who doesn't know why they're switching the wires would go a looooonnggg way towards bridging the gap between opponents and the proponents of DBTs...."

COMMENT
As I say, when you give up fast switching, you give up sensitivity, and if you do fast switching (unless a signal generator is used!), then you need a switcher and some extra wire.

The basics are covered in the Rules.

http://www.audioasylum.com/audio/dbt.html

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