What is the normal pitch acuity for melodic steps?
Ah, this is a vexed question. Almost guaranteed to start a heated discussion in some circles. It is far greater for notes played in chords since you can listen out for the beats. If it is a nice rich harmonic timbre with many partials then some of the higher partials may beat rapidly and be fairly easy to hear (or learn to hear), at least as a sort of roughness in the texture, or indeed as beats. But here we are talking about melodic steps rather than chords. One may not be able to hear the distinctions between the various interval sizes as melodic steps necessarily as that depends on ones pitch acuity – the distinction between the pure and tempered major third for instance is only 14 cents, and some find that quite a small interval to distinguish. One can learn to distinguish finer pitch distinctions with practice. A fine analogy here I feel is with night vision. When you first look through a telescope at a faint galaxy you may not see anything in the field of view at all, but if told
