A new study by the Audio Engineering Library has found MP3s and other forms of compression have a serious impact on the "timbral and emotional characteristics" of music.
As reported by What Hi-Fi, the research tested a range of compressed files against 10 emotional characteristics and found negative ones such as sad, shy and scary were increased, while positive characteristics such as happy, calm, comic and romantic were reduced.
Interestingly, the study — titled The Effects of MP3 Compression on Perceived Emotional Characteristics in Musical Instruments — found that anger was relatively unaffected.
As to why MP3s boost negative characteristics, the study suggested the cause is background "growl" added by compression.
Apparently the instrument most affected is the trumpt, while that least affected is the horn. All the more reason to listen to full-quality audio then, not that we needed convincing...