Thanks @djones51 , I will try that. I'm not sure if the variation is "big" or not. I am very sensitive to tonal imbalances, so it could in fact be very small. Although my wife can immediately hear it as well.
Also, while it is blatantly noticeable on many tracks/artists/recordings, especially if there is not a lot of reverb in the recording, mostly being apparent in upper ranges of vocals (singers sound "fleshed out" in the upper ranges on the left but not the right), on many tracks the effect is very, very subtle.
@djones51 I will try your suggested "imperfect" test. But I'm curious, what would the perfect test be?