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ABXTEST(1)		      MPEG Audio Decoder		    ABXTEST(1)

       abxtest - double-blind ABX comparison testing script

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

       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 be-
       tween 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.

       -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.

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

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

       abxtest	uses  the  binomial  distribution  to accurately calculate the
       probability that	the result is the same as random guesses.

       Robert Leslie <>

MAD			       16 November 2000			    ABXTEST(1)


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