There is no agreed standard for Mastering recorded music right now.
ONLINE PLATFORMS - iTunes, Spotify, YouTube, Soundcloud ... they all playback at different loudness levels to each other, and most of them will adjust the level of your tracks after you upload them if they don't fit their particular criteria.
PHYSICAL MEDIA - tape, CD & vinyl generally have different loudness "standards" to online platforms, and to each other.
So the idea that one set of masters for your recordings will work perfectly for all your delivery platforms & formats isn't really true, and definitely can't be presumed.
Communication with your mastering engineer is key to making sure your masters are suitable for however you want to release them. It's possible to find a good compromise between the demands of different media, but only if your mastering engineer knows what your release plans are. They'd be doing you no favours by making a master that would be great for CD but totally unsuitable if you were pressing vinyl!
Getting it right can be a complicated business so we're always happy to chat about your mastering job before you decide whether or not we're the right choice for you.
Free Test Master