> It happened more than once to me that some instrument had been detuned a semitone up or down and I noticed because the resulting music felt different. I susp

> It happened more than once to me that some instrument had been detuned a semitone up or down and I noticed because the resulting music felt different. I suspect this is you having some amount of absolute pitch? It's pretty common! What's rare is reliably and quickly identifying pitches without a reference, though even this can often be learned with practice.