The following excerpt comes from The Conscious Ear by Dr. Alfred Tomatis, page 69-70. A French ear, nose and throat doctor who died in the early 2000’s, Tomatis  is considered the father of psycho-acoustics, the study of how the central nervous system processes sound.  This is a great book to understand more about how the ear is involved in our ability to learn, speak, express, sing, etc.

Below, what Tomatis is talking about is that he put special headphones on people that allowed him to filter out certain frequencies, narrowing the bandwidth. Depending on what frequencies he filtered out, people reacted or behaved differently. As well their posture changed.
The main way that .mp3 and other similar compression formats take out data is not exactly the same as what Tomatis was doing in his experiments,  but they are filtering out certain frequencies and in ways that are more difficult for us to consciously notice. However, some of the symptoms are the same, particularly over the long-term, A few hours of listening to .mp3 files is not going to make a difference. Over months and years the effect will be seen as is illustrated in the article, “Kids prefer poor quality MP3” also found on this website. For an in depth, technical description of .mp3 lossy compression from the magazine “SOS” (Sound On Sound) click here.

P 69-70 “…all that I discovered about the involvement of the body in vocal utterance I established that the physical behavior of my patients varied according to the frequency range they heard, that is, according to the type of listening which I imposed on them. Their attitudes and reactions to psychological stimuli of the same type and intensity were all modified when they passed from one mode of listening to another. I saw them collapse or puff out the torso, expand or retire within themselves, become enthusiastic or lose muscle tone………for example, a certain singer to whom I ‘gave the ear’ of Mario del Monaco [famous singer in the 1930’s and 40’s in France] gained, in a year, four or 5 inches in measurement around the thorax [chest]. It was as if learning to hear and applying their audio-vocal control differently actually transformed their way of breathing…In the case of other singers on whom I imposed different types of listening, various different phenomena appeared. Some changed their posture, holding themselves more and more upright with their head slightly bent forward. Others manifested a quickening or a slowing of their heartbeat. Their entire neurovegetative [autonomic nervous system] life was thus revolutionized.”

Summary: The effect, then, of listening to a reduced frequency spectrum over time will change the neurovegetative process in the body, affecting posture, attitude and behavior, learning, expression and the quality of the voice.