How are we able to distinguish different types of instruments playing together in a concert?

I recently heard about the idea of biophony In one article, it said that the sounds made by different species were like the instruments in an orchestra. In order to get a handle on this, I would like to know how we can recognize the different instruments that are playing at the same time. Do they have different frequencies? I thought they were playing the same notes. Why is it that, for example, we can make out a piano, cello and horn playing together? On the other hand, why is it that a lawn mower or jackhammer seems to blot out all other sounds?