I have some rare old music files on my drive that are compressed to 128 kbps in the mp3 format. Some of them are of digital origin, and some of them are vinyl rips.
Audio data compression affects music in a variety of ways. For a pretty in-depth explanation, this article by SOS Magazine may be helpful. Mentioned effects are:
- Decreased Frequency Response
- Lower Dynamic Range and Mutated Dynamics
- Loss of Frequencies
- Frequency Anomalies and Distortions, Swirlies
- Pre- and Post-Echoes
- Audio Content Timing Errors (Roughness & Double-speak)
- Loss of Transients and Sound Details
- Loss of Stereo Imaging and Panned Details
- Phase shifts
- Noise addition
I am not an expert in any of these effects, and there may be more effects, so I encourage you to read all about it.
I am however interested in learning if there are ways to try to "recover" or at least "improve" bitrate-compressed audio files. It is probably near-impossible to restore them to their original state. But can they be adequately recovered or at least improved?
If so, which methods are used? What kind of expertise would be needed? Are there universal tools or utilities that can help along the way?
Also, could an amateur musician (like me) use common mastering/mixing tools to at least improve the files a little using EQs and whatnot – or does the ‘shit in, shit out’ principle apply?