With the exception of instances where you would already have a good idea what the answer is, for instance few John Williams scores contain any form of electronic instruments. I know from interviews that all of Mass Effect 2's soundtrack was done electronically, with the exception of cello samples in certain songs. But can you tell if a track is completely synthesized, or partially synthesized, and single out specific instruments that weren't performed by live orchestra versus those that were? A soundtrack having high production value doesn't mean that it isn't a live recording that was edited to death in post. Obviously with movies, if there exists a recording session then everything you're hearing is live orchestra, right? Or do they integrate synthesizer soundboards into the recording process itself? But mostly I'm asking about scores where a recording session isn't readily available, like video game scores.

tl:dr basically just read the title

Yes, I think i can hear the difference. If you compare the Star Wars Main Title from episode 4 and 7 the newer version sounds like crap :( I think the recording of the trupets etc. are live recordings but they used a ton of auto tune...
If you listen to Hans Zimmer, nearly everything is synthesized

It's very easy to tell if you're listening to sampled brass. It lacks vitality, punch.

The Force Awakens was not synthesized. It may not be as good a performance but that has nothing to do with real vs synth.

I've always wondered whether Thomas Newman was using real strings or not, especially on Road to Perdition. The orchestra sounds so mellow and soft, I hear absolutely no ambience sounds. It almost sounds too perfect for a real-life recording.

i certainly do know when i hear f**** audiomachine :v

Most musicians will have this ability after some time playing their instrument, which one would expect from a musician after they spend years honing their abilities as well as learning theory.

This trained 'pitch perception' is something that musicians can acquire over time.

Some people however can for some reason start off having a good ear for pitch. I'm not sure what the science of this is but I've seen some children who can learn to play an instrument relatively quickly and can transcribe easily.

I was one of those kids. I would ask my teacher what the names of songs were by playing them on the piano to him and started improving piano duet fairly early on too. So I consider myself quite lucky, unfortunately I wasn't blessed with the psyche to become a performer so much and thus never really worked as hard as I should have playing piano - I'm still working on that :D

I looked musical aptitude up on wikipedia which lead me to some studies by Carl Seashore who done extensive tests on the 'Measurement of Musical Talent' which I guess should be taken lightly since it is related to IQ which in itself is a disputed field.

You could always read this article on wikipedia and it might have some good links to studies or writings in this field. It's quite extensive, hence why I decided to link you up instead of copying the same information across.

I wouldn't be able to tell unless it was percussion or synth-like (like beep boop noises) instruments... like, the Batman Arkham franchise, the soundtracks actually sound like a real-orchestra but I'm sure they were synthesized. Hopefully someone who's listened to those soundtracks can confirm.

Kind of a 'Catch 22' question. If you can't tell, then how do you know if it is or isn't?

Certainly sometimes you can hear something is off. Perhaps that every note is separate, rather than flowing together.

Every musician also has a unique style, while a machine plays how it is programmed to.