Headphones

Same amp with multiple DACs connected at the same time, volume matched. Just switch the source and can easily tell differences. Maybe a 1 second gap in doing so. Focus on specific aspects of sound like perhaps a guitar you hear at extremes of left and right. Evaluating 2 R2R DACs that way the lesser one almost eliminated the guitar and what there was of it was in the center. With other comparisons there can be big differences in clarity or even hearing portions of music suddenly gone. Generally a skeptic with a science background so well aware of placebo effects and such. The differences I've heard in DACs have ranged from minor to significant. Makes me wonder how others can't hear these obvious differences. Though if it was 30 seconds or more between switching sources I wouldn't trust my auditory memory.