Research undertaken by Hong Kong University of Science and Technology and initially published by the AES (Audio Engineering Society) has found that using a compressed audio format (such as MP3), introduces subtle perceptual differences between recordings of various musical instruments.
It was noticed that increased compression led to a change in the “emotional characteristics” of various instruments. The research showed that motions considered neutral and negative (mysterious, shy, scary and sad) tended to be heightened, whilst more positive emotions (including happy and romantic) appeared to be diminished.
So unless you really want your recordings to induce an air or despondency, perhaps avoid using these formats!