SYNOPSIS

       abxtest [-n min] [-m max] [-g goal] A-cmd B-cmd


DESCRIPTION

       abxtest  is a tool for conducting listening (or other sub­
       jective) tests to determine whether a listener can discern
       a  difference  between  two subjects under test, denoted A
       and B.

       The listener conducts several trials in which  an  unknown
       subject,  X,  is randomly chosen to be either A or B.  The
       probability that X is A or B is  the  same.  The  listener
       must  decide whether X sounds the same as A or the same as
       B.  The listener may repeat A, B, and X as many  times  as
       necessary before reaching a verdict.

       In  order to prove the hypothesis that a difference can be
       discerned between A and B, the listener must disprove  the
       null  hypothesis  that  A  sounds  the same as B.  This is
       accomplished by correctly identifying X often enough  that
       randomly guessing correctly the same number of times would
       be statistically improbable.

       The A and B subjects for abxtest  are  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  of  X.   The
       listener  may  interrupt  an executing command (usually by
       pressing ^C) without terminating the test.


OPTIONS

       -n min Set the minimum number of trials. Trials will  con­
              tinue  after  this number if the statistical proba­
              bility goal has not yet been met.  The  default  is
              10.

       -m max Set  the  maximum number of trials. Trials will end
              after this number even if the statistical probabil­
              ity goal has not been met. The default is 20.

       -g goal
              Set  the minimum statistical probability goal. This
              is the probability that the number of correct iden­
              tifications 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/random
              By default this file is read to generate  a  random

       Robert Leslie <rob@mars.org>



MAD                      16 November 2000              ABXTEST(1)

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