A-B-X Test refers to that method of comparing a change in a component or sound quality when three audio sources are available. A and B are the original audio source and the original audio source with some modification to the signal path or sound quality. The third source, X, is the same as either A or B. An assistant selects among the sources while the listener attempts to determine which two are the same and which one is different. The test is repeated enough times to ensure non-random results.