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
probability 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)