ABX test

An ABX test is a method of comparing two choices of sensory stimuli to identify detectable differences between them.

ABX tests can be used to audition input, processing, and output components as well as cabling: virtually any audio product or prototype design.

This extraneous cue was removed by inserting a fixed length dropout time when any change was made.

The dropout time was selected to be 50 ms which produces a slight consistent click while allowing subjectively instant comparison.The ABX company is now defunct and hardware comparators in general as commercial offerings extinct.

Myriad of software tools exist such as Foobar ABX plug-in for performing file comparisons.

If only one ABX trial were performed, random guessing would incur a 50% chance of choosing the correct answer, the same as flipping a coin.

By increasing the number of trials, the likelihood of statistically asserting a person's ability to distinguish A and B is enhanced for a given confidence level.

[2] The company QSC, in the ABX Comparator user manual, recommended a minimum of ten listening trials in each round of tests.

[3] QSC recommended that no more than 25 trials be performed, as subject fatigue can set in, making the test less sensitive (less likely to reveal one's actual ability to discern the difference between A and B).

Important decisions are normally based on a higher level of confidence, since an erroneous significant result would be claimed in one of 20 such tests simply by chance.

The foobar2000 and the Amarok audio players support software-based ABX testing, the latter using a third-party script.

Simply looking at the outcome totals of the test (m out of n answers correct) cannot reveal occurrences of this problem.

In this regard, forced-choice tests such as ABX tend to favor negative outcomes when differences are small if proper protocols are not used to guard against this problem.

Typically, control conditions include the presentation of unimpaired audio materials, introduced in ways that are unpredictable to the subjects.

It is the differences between judgement of these control stimuli and the potentially impaired ones that allows one to conclude that the grades are actual assessments of the impairments.3.2.2 Post-screening of subjects Post-screening methods can be roughly separated into at least two classes; one is based on inconsistencies compared with the mean result and another relies on the ability of the subject to make correct identifications.

However, bearing in mind the variability of subjects’ sensitivities to different artefacts, caution should be exercised.

Since ABX testing requires human beings for evaluation of lossy audio codecs, it is time-consuming and costly.