# FreeBSD Manual Pages

ABXTEST(1) MPEG Audio Decoder ABXTEST(1)NAMEabxtest - double-blind ABX comparison testing scriptSYNOPSISabxtest[-nmin] [-mmax] [-ggoal]A-cmdB-cmdDESCRIPTIONabxtestis a tool for conducting listening (or other subjective) tests to determine whether a listener can discern a difference between two subjects under test, denotedAandB. The listener conducts several trials in which an unknown subject,X, is randomly chosen to be eitherAorB. The probability thatXisAorBis the same. The listener must decide whetherXsounds the same asAor the same asB. The listener may repeatA,B, andXas many times as necessary before reaching a verdict. In order to prove the hypothesis that a difference can be discerned be- tweenAandB, the listener must disprove the null hypothesis thatAsounds the same asB. This is accomplished by correctly identifyingXoften enough that randomly guessing correctly the same number of times would be statistically improbable. TheAandBsubjects forabxtestare actually arbitrary shell commands. The normal mode of use would be to give commands which play two slightly different sounds. The standard output and standard error from each command are suppressed so as not to reveal the identity ofX. The listener may interrupt an executing command (usually by pressing^C) without terminating the test.OPTIONS-nminSet the minimum number of trials. Trials will continue after this number if the statistical probability goal has not yet been met. The default is 10.-mmaxSet the maximum number of trials. Trials will end after this number even if the statistical probability goal has not been met. The default is 20.-ggoalSet the minimum statistical probability goal. This is the proba- bility that the number of correct identifications is the same as random guesses. In order to disprove the null hypothesis, the result of the test must be a probability less than or equal to this goal. The default is 0.05.FILES/dev/randomBy default this file is read to generate a random sequence ofX.ENVIRONMENTRANDOM_FILE If set, the file named by this variable will be read instead of/dev/randomto generate a sequence ofX.NOTESabxtestuses the binomial distribution to accurately calculate the probability that the result is the same as random guesses.AUTHORRobert Leslie <rob@mars.org> MAD 16 November 2000 ABXTEST(1)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | FILES | ENVIRONMENT | NOTES | AUTHOR

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