Over years of evaluating differences in audio equipment, one accumulates an audible library of sonic cues from which to judge differences. Cues such as harmonic overtones, extended decay, room modes in the recording, placement, soundstage dimensions. The list is actually quite long.
For those of us with big libraries in our heads, it may not be easy to remember how overwhelming it can be for newcomers evaluating differences in equipment. I can certainly recall hearing so many differences that singling out one from the many felt impossible—like picking a single face out of a crowd of thousands.
When asked for advice on how to get comfortable with the evaluation process, my go-to answer is to keep it simple and easily identifiable, like a singer and acoustic guitar, two easily recognizable instruments.
Often, the mistake newcomers make is to jump feet first into the big and complex pieces of music, hoping the expected improvements will wash over them like a tsunami. This often leads to disappointment.
Better to keep it simple.