So I decided to do a comparison between uncompressed audio files and the best way encoded mp3. I'm sorry if something like that was already posted or analysed here before, I just thought I'll share, since it was quite fun to experiment.
I did this experiment with several different types of uncompressed audio music files, but what you see here is “S. Rachmaninov’s - O come and worship” choir, one frame sample. Choir is usually quite sensitive to compressions.
I must admit I could not actually here any difference between flac and mp3-320kbps with my sennheiser hd595 on 0 eq even in a completely silent room. However I’ve noticed some minor difference between highest VBR mp3 and uncompressed source, so at least it says something. With better equipment (...good amp, hd 650 maybe or better) I believe you could here a difference even on 320kbps.
Anyway hope this helps for someone who is interested in this as I've noticed people discuss a lot about quality of FLAC or APE vs mp3.