They’ll know the difference. But they won’t necessarily care about it anywhere near as much as some of us might
You can fake an upright-ish sound in a variety of ways. One of the easiest and most effective ways to get it is to just approach and play the bass line like a string bass player rather than a bass guitar player would.
The upright vibe is as much a matter of convention and style as it is the sound itself. Most times it’s better to hint at or imply an upright bass and let the listeners connect the dots rather than try to duplicate the actual sound. (Which you can’t anyway.)
If you want to have some fun, keep a stool nearby if you’re going to do the upright thing. When you go into upright mode just park the tail of your bass on the stool, hold it vertically and play it like you would an upright while copping as much of an upright style as you can manage. It almost always (except around serious jazzers) goes over well.
I used to do that occasionally when I finally stopped playing an upright. People would tell me it “sounded just like an upright bass.” Amazing what a close enough sound, the correct style, and a blatant visual cue can do to encourage someone’s imagination to fill in the missing pieces and turn a blind eye to what’s not quite right.
Ain’t gestalt psychology a grand thing?
‘Cuz here’s the thing…I played upright almost exclusively for the first five years I played bass and in varying amounts for several more years after that. So I’m intimately familiar with the timbre and presence you get with the real deal. And because of that, no emulation is ever likely to completely satisfy my ear.
However…and here’s the important part…the less exposed to and familiar people are with the sound of an actual upright bass (which is most people these days) the easier it is to convincingly emulate one
for them.
So it might be best to take the advice of some of the earlier posts that suggested forgoing verisimilitude and concentrating primarily on the vibe and feel and shoot for something “close enough for everyday use” instead.
Because in this case it really is mostly in the hands.
Luck!
