Mastering in 2019
As a means of understanding just what a potential minefield mastering is today, consider the requirements of a mastering engineer role during the CD era. The music industry in those pre-internet days was a much smaller place, with an emphasis placed on "high quality". Hi-fi enthusiasts would buy a choice amplifier, a pair of speakers, and a CD player, and having spent a fair extortionate amount of money on the CD itself, would return home, effectively looking to recreate the precision environment in which the record was mixed and mastered in the comfort of their own home. This period represented a kind of 'audio pinnacle', where there was a genuine desire to preserve the detail which had gone into the creation of a record during the playback stage.
Music makers continue along this same path today; we invest in acoustically treated studios, make careful decisions about our monitors and headphone choices, and how to apply more EQ and dynamic settings, as the very process of 'getting better' at music production involves us getting better at decision-making we apply to our own productions.
But whereas once upon a time, you could almost guarantee that your mixes would be played back through a high-quality listening system, the means by which consumers listen now is quite watered down compared to it's potential form.
In recent years, streaming services have taken center-stage as a replacement for physical media in terms of popularity, which means that we're mostly consuming music when we're plugged into the grid, whether that be through smartphones, tablets, or on computers. While streaming platforms provide fast access to a broader range of music than ever before, their formats are often 'lossy', meaning that in order to stream quickly, the file sizes are smaller, squeezing out various information from the music file in the process.