Perhaps it would be helpful to know a bit about how the original mp3 codec was developed.
Fraunhofer used groups of people in listening panels as they tweaked the compression algorithm. The goal was to create a format that people could not discern a difference between compressed audio and uncompressed sources.
They eventually developed a comp format that most people in the groups could not tell the difference beyond the random rate. mp3 is not simply applying computing power to some form of lossy data format.
After they had felt they had a codec that was appropriate, they tested it a final time in public forums. In this final test, the subjects were in the order of 18,000 listeners, who were not made aware that they were listening to compressed lossy audio. The contract was between Fraunhofer and the National Hockey League (NHL) who used mp3s as the source for in-game music interludes, for two years.
Only then did the mp3 codec become available to computer software audio via a licensing agreement.
So, if you can't tell much difference between mp3 and uncompressed audio, don't fret. It was designed in such a way that it would be the outcome when played in average quality reproduction.
The areas where mp3 differs from uncompressed audio are precisely the same areas where above average Sound Quality (SQ) audio systems excel versus more mundane reproduction. So, if you want to hear the differences, you must start with an above average sound system. The least expensive route would be via a quality headphone amplifier and an excellent pair of 'phones.
AAC, developed a decade later, improves on mp3's ability to "hide" the fact it's a lossy compression format. So, it's even more difficult to hear the differences unless you are using above average gear in in-home audio systems or a deliberate SQ-oriented amp & 'phones combination.
There are a small minority of people who can readily identify mp3 or AAC versus lossless beyond the random rate. For most people, that is ordinary listeners without trained ears, it is difficult.
"Trained Ears" would refer to people who can, for example, hear low levels of harmonic distortion below the average listener's level.
There is one other thing worth mentioning. Once you employ lossy compression on a song, you have changed it forever. The bits thrown out cannot be reconstructed, ever.
In our current world, hard drive space is inexpensive and of massive storage capacity. So, there is little penalty to storing lossless files, or both lossless originals and AAC or mp3 copies, each to be used as appropriate for the listening equipment.
In this way you can be assured that as computing power increases (say, a new lossy format is released at some future date that is even more difficult to discern) you could always create the "better" lossy file for your listening pleasure.
For this reason I suggest you consider using FLAC or actual disks as your source of music files. You can always create lossy format files from those, now and forever.
