QSC ABX Comparator User Manual page 4

One trial is not enough; even flipping a coin to decide which amp is X would yield the right result about half the
time. No, it takes repeated trials, with X randomly selected each time, to get a statistically significant test. If
the listening judge answers correctly in only about 50% of the trials, he or she didn't hear any audible difference
between the amps. But if far more than 50% of the answers are correct, the listener clearly discerned some audible
difference.
Notice that the decision made in each trial isn't "which amp sounds better?" Instead, the goal is to identify whether
the amps sound totally alike or different; deciding which is better sounding is a job best left for later. You can't
judge whether one amp sounds better than another unless you determine that they actually sound different!
The ABX Comparator not only automatically and randomly selects the amplifiers, but also tracks the choices the
listening judge makes in each trial. After a sequence of trials, the ABX will report how many trials and how many
correct answers the judge made.
II. DESCRIPTION
THE ABX COMPARATOR
Calibration
Power switch voltmeter display
O N
P O W E R
Front panel
The front panel features a power switch, a digital voltmeter display (for calibration), an alphanumeric LCD display,
eight input and control buttons, and a female 8-pin DIN connector. During operation, menus, instructions, and
data appear on the LCD display.
Binding post signal terminals
B CH1
A
INPUT
M
P
B CH2
Rear panel
The rear panel has input and output connectors, a 9-pin RS-232 port for connecting to an optional computer,
and an additional RS-232 port for slaving one or more additional ABX units.
4
LCD display UNIT A button UNIT X button UNIT B button ENTER button
D A T A
CALIBRATE button
"Combo"signal connectors
CH2—LINE OUT—CH1
CH1 A
A
OUTPUT INPUT
M
P
CH2 A
P 1=G
P 2=+
P 3=-
U N I T A X U N I T B E N T E R
C A L I B R A T E T R I A L R E V I E W S C R O L L
TRIAL button REVIEW button SCROLL button Infrared sensor
CH2—LINE IN—CH1 CH2—LINE OUT—CH1
B
A B X 1
A B X C O M P A R A T O R
(for remote)
RS232 to optional AC power
computer connection
A
RS232
REPLACE
FUSE WITH
QSC AUDIO
SAME TYPE.
PRODUCTS INC.
SEE USER'S
MANUAL FOR
SLAVE
RATING.
MADE IN
U.S.A.
RS232 output
to slave ABX
R C