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ABXTEST(1)		       MPEG Audio Decoder		      ABXTEST(1)

NAME
     abxtest - double-blind ABX comparison testing script

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

DESCRIPTION
     abxtest  is  a tool for conducting listening (or other subjective) 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 statis-
     tically 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  dif-
     ferent sounds. The standard output and standard error from each command are
     suppressed  so as not to reveal the identity of X.  The listener may inter-
     rupt an executing command (usually by pressing ^C) without terminating  the
     test.

OPTIONS
     -n min
	    Set  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.

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

     -g goal
	    Set the minimum statistical probability goal. This is the  probabil-
	    ity 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 de-
	    fault is 0.05.

FILES
     /dev/random
	    By default this file is read to generate a random sequence of X.

ENVIRONMENT
     RANDOM_FILE
	    If set, the file named by this variable  will  be  read  instead  of
	    /dev/random to generate a sequence of X.

NOTES
     abxtest  uses  the binomial distribution to accurately calculate the proba-
     bility that the result is the same as random guesses.

AUTHOR
     Robert Leslie <rob@mars.org>

MAD				16 November 2000		      ABXTEST(1)
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