9
THE TEST SESSION BEGINS
NOTE: To preserve objectivity in the test, don’t tell the listening judge before or during the trials
which amplifier is A and which is B. Otherwise, if he or she has even a slight prejudice toward or
against one amp, they may try to pay attention to “does Amp X sound like Brand Z” instead of to
whether the amps sound alike or different.
Instruct the listening judge:
1.
Each trial starts with the X, or unknown, amplifier, which could be either Amp A or Amp B. Compare
its sound with that of Amp A, by pressing the
A
button, and to Amp B, by pressing the
B
button. You
can switch to X by pressing the
X
button. You may freely switch back and forth among Amp A, Amp
B, and Amp X as much as you’d like before you enter your choice. Listen carefully. Does X sound like
A, or like B?
2.
To register your choice with the ABX Comparator, press the button—either
A
or
B
—of the amplifier
that you believe is X, the unknown. Then press
ENTER
.
3.
The ABX will not tell you if you were right or wrong; instead, it will immediately go on to the next trial,
randomly selecting which amp will now be X. In the this new trial, X might be the same ampilfier as
in the preceding trial, or it might be the other amp. Don’t let your previous evaluations influence your
current one.
Repeat this procedure for each trial.
The ABX unit switches only the amplifier outputs to the speakers, and not the audio signal to the amps. This
prevents the listener from getting visual cues from the amplifiers’ front panel LEDs or meters.
ENDING AND REVIEWING THE TEST SESSION
You can end the test session at any time by pressing the
REVIEW
button on the front panel of the ABX, or you
can just have the evaluator perform all 25 trials. Remember, the more trials you conduct, the more statistically
significant your results will be.
If you press the
REVIEW
button, the ABX will ask you whether you want to enter review mode. Press
A
if you
do, but if you want to continue with more listening trials, press
B
, then go ahead and do some more trials.
In review mode, the LCD display will show how many times the listening evaluator identified X correctly, out
of how many trials, and the percentage. To view the result of each trial,
press the
SCROLL
button. Each time you press the
SCROLL
button, the
display will step to the result of the next trial.
OBTAINING STATISTICALLY SIGNIFICANT RESULTS
Given only two possibilities in each trial, a random selection of A and B, such as each selection being based on
coin toss—or even just selecting the same one every time—would tend to yield correct results about 50% of
the time. In a small sample, i.e., a small number of trials, the actual results may be wildly different from 50%,
Summary of Contents for ABX Comparator
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