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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 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  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 default is 20.

       -g goal
	      Set 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/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
       probability 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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