Ah, now I understand - it all comes clear: you genuinely think "properly built DACs" all sound alike. Clearly you very, very badly need to get your hearing checked, and soon.
perceiving a difference is easy. to the point where you don't even need a difference to perceive one. but it's important to properly qualify which perceived differences count and which do not. that in turn will form the basic criteria for your listening test:
- it can feel silly, but when you see 2 different DACs clearly looking different, that has been demonstrated to be more than enough to feel like the sound is different. it might not happen for everybody the same way, and what we were told about both DACs can certainly increase the belief that they are very different, and the expectation bias resulting from that. because that is a possibility and it has been clearly demonstrated to be one so many times with so many people, a listening test requires that the listener doesn't know what he's listening to during the test. if not, we can never be sure that we didn't "hear" with our eyes. and to be plainly clear, those who think they're not concerned by this are wrong.
- DACs very often have audible difference in the output volume level. does that qualify as audible difference? it's a difference in sound and it's audible so I guess yes, but should we purchase a DAC because it was 2 or 3dB louder than another one? doesn't seem like a very good reason to me. so I would suggest to always make sure the levels are very closely matched when we do a listening test between DACs.
- another side effect of the potential difference in output voltage for the DAC, could on occasion be that the voltage exceeds or is far below nominal values for the amplifier's input. most of the time I wouldn't expect a difference, but on occasion that results in distortions more or less noticeable, or if the gain needs to be drastically increased, sometimes it will be the difference between having noticeable background hiss or not. in the context of a given playback system, that could be very important, but when judging DACs on their own for their fidelity, it would be utterly unfair to blame what happens to the amp on the DAC. so once again, proper volume matching between the DACs tested seems like a pretty important step. at least for those who wish to avoid spitting on a DAC because of their own errors when picking the amp or gain settings to pair them with.
now in practice, once you start testing DACs while paying attention to what are really just 2 obvious requirements(avoiding subjective bias to ruin the test, and checking that we output the same volume level), suddenly the number of DACs clearly sounding different drops like a stone. to the point where many people haven't experienced 2 DACs sounding noticeably different to them. it could obviously be that those who don't meet such situations simply lack in experience, hearing skills, or simply have purchasing criteria that will eliminate the weird DACs, massively limiting the opportunity to listen to one. so them not noticing differences doesn't mean DACs with a unique sound don't exist. also if their idea of a properly built DAC is that it will sound like another properly build DAC, then the condition is self fulfilling and they're technically right, but that doesn't mean much for DACs in general ^_^.
but on the other hand, anybody ignorant about gears, himself, or how to conduct a controlled listening test, would naturally be tricked by his own impressions from time to time, and as a result, would become convinced that they often and easily notice differences between DACs(and really between anything and anything else). it's one of those typical situations where being less qualified results in feeling like we're doing better. so for us to trust you're not just fooling yourself, we could really do with some supporting evidence.
