And how do I know that I'm good/decent/bad at ear?

[caick1000]

And how to practice to be good at ear?

So I'm kinda new to piano (don't have much time to play everyday..) but I saw a lot of people like hearing a piece and just play it without using a piano sheet and all.
That means that those people that are good at ear can differ all different instruments in a concert? Say like "Oh I can hear that this piece use this this and this instrument"

I for example can't really differ much the intruments if they're "similar" like the viola and violin or the horn and the euphonium. But I can ofc if it's a violin and a trumpet or piano because it's kinda obvious.
Any way to improve this or I just need to keep hearing many pieces/concerts until I'm confortable with it?

[mishamalchik]

It really is just practice. Honestly. I think almost every kind of ear training is just practice with the possible exception of perfect pitch. Having said that, I had no real piano training until I was 19 and discovered only after a few months of religious practicing that I have gained perfect pitch. I actually realized I had it from playing by ear because my sight reading ability is atrocious and I actually didn't confirm it until my first music theory class, in which I couldn't distinguish an oboe and an English horn, but I could tell you what notes they were playing.

Ear is just a matter of getting familiar with timbre, tone and pitch.