Bernard, a basic requirement for a blind listening test of electronic equipment is that the levels be matched to within 0.1dB. The reason for this is that in some tests using test tones an overall difference of as little as 0.2dB has on occasion been detectable, not as a loudness difference as such, but possibly perceived as more clarity, better imaging, etc. This also explains some differences reported in casual non-blind listening where the listening levels weren't carefully matched.

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Enjoy the music, not the equipment.