The secret of an upright (and it cannot be replicated on a bass guitar) is the sluggishness of its attack and how the percussive aspects of the instrument's sound almost drown out the tonal ones in the low registers. I saw Neil Diamond some months back and he had about a dozen musicians including a bassist who insisted playing upright for most of the set. Without looking up, you could always hear when he played the electric bass guitar, there was just so much more tonally identifiable note to latch onto. The upright was neither not loud enough nor mixed badly, but to discern whether he was playing a root, a fifth or a third always took some concentration for his bass lines.
