QSC ABX Comparator User Manual page 3

ABX Listening Test Comparator
I. INTRODUCTION
The ABX Comparator is a signal routing and measuring device that permits simple and accurate comparative
listening tests of two or more power amplifiers or even line-level audio components. Using advanced
microcontrollers, the ABX Comparator's features and functions allow you to quickly set up and conduct sessions
of critical listening test trials for performance evaluations.
Key features include:
• A built-in test tone generator and digital AC voltmeter for fast calibration of amplifier levels.
• High-speed relays for fast switching between amplifiers under test.
• A single pair of speaker outputs, for true accuracy.
WHY USE AN ABX COMPARATOR?
Comparison tests between amplifiers are often plagued with these unintended but very real inconsistencies that
lead to inaccurate auditions:
Unequal input sensitivities This leads to one amplifier being louder than another. Even experienced
critical listeners often confuse differences in volume with differences in audio quality.
Different speakers used with each amplifier The difference in frequency response between two
loudspeakers, even of identical models, can often be several dB. This can easily mask differences in
amplifier audio quality.
Slow switching between amplifiers Your "audio memory" is short-lived. You won't catch small sonic
differences between amplifiers unless switching between them is quiet and fast (under 50 ms).
Unconscious bias Even when you try to be truly unbiased, your unconscious mind often leads your
conscious mind subliminally to bad conclusions, as in a "This is a Brand A amp, and this is a Brand B—
which sounds better to you?" type of test. The solution is to have the listener completely unaware of
which amp is which, even in the inital audition. This is called double-blind testing, and it's the only
way to get a truly unbiased result.
The ABX Comparator has been specifically designed to eliminate all these errors.
THE ABX TESTING PROCEDURE
The letters "ABX" describe the listening factors used in double-blind testing of two amps. One amp is "A" and
the other is "B," and the two have been set up so that they put out precisely the same output levels. "X" designates
the unknown factor—is it A or is it B? Thus, every time the ABX Comparator randomly selects "X," which could
be either A or B, the person judging the amps will compare it to amp A and amp B (all the while paying attention
to detect audible differences between the two). The challenge then is to identify X. And this is truly "double-
blind" testing, so the listening judge doesn't even know which amp being tested is A and which is B, but must
nevertheless decide whether X is A or B.
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