Remastering is the process of taking an existing audio master recording and re-processing it — typically using modern equipment, techniques, and digital tools — to create an improved version optimized for current playback systems. A remaster may adjust equalization, dynamics, stereo imaging, noise reduction, and overall loudness to make the music sound its best on today's speakers, headphones, and formats.
Not all remasters are created equal. The best remasters go back to the original analog master tapes and carefully transfer them using high-quality analog-to-digital converters (for digital formats) or cut new lacquers directly from the analog tapes (for vinyl). Poor remasters may use lossy digital sources, apply excessive compression (the "loudness war"), or alter the sonic character beyond what the original artist intended.
For vinyl collectors, the remastering chain matters enormously. An "all-analog" remaster — where the original analog tapes are used to cut a new lacquer without any digital conversion — is considered the gold standard by audiophiles. However, excellent results can also be achieved with high-resolution digital intermediaries (96kHz/24-bit or higher). The key is the skill of the mastering engineer and the quality of the source material.
The 2009 Beatles remasters took four years to complete and were overseen by the original albums' mastering engineer's son, Sean Magee, at Abbey Road Studios.