What I do NOT want to do is create a replication of the ancient 'web directory' or replicate what sites like KVR & etc do. Rather, these should be things that aren't in common use at the time we post them or offer novel usages, simplify modern workflows or even just offer what was once boutique pricing for a task at a low or free price point.
Let's start where most of us end, with a discussion on the tools used to deliver our material to the platforms that are distributing and streaming to our audiences today....
Mastering tools for modern publishing platforms:
Most of the larger streaming & online music distribution platforms have finally brought relief to listeners from levels jumping radically track to track through the widespread adoption of a variety of normalization algorithms. Thankfully, rather than just compressing & limiting based normalization as was used in the broadcast industries, scan & index systems like ReplayGain (RG) have come to the fore for many of these platforms. You might be familiar with this through the open source community (hydrogenaudio) and tools such as Foobar2000 and other tools that target the home audiophile & digital album collectors alike.
For instance Youtube Music apparently has chosen to use the BS.1770 standard which is also now known as LUFS [also known by the older non-standard term LKFS pioneered by Bob Katz]. Here's a good breakdown on edmprod.com that breaks this down with software tools that are easily accessible to our DAW workflows: LUFS: How To Measure Your Track’s Loudness in Mastering (I will also link some of these below to highlight them for fellow Scopers).
Note those of you who come from a traditional broadcast background might find the following inquiry to be more digestible: Using the ITU BS.1770 and CBS Loudness Meters To Measure Loudness Controller Performance
When it comes to understanding how your material will translate to these platforms, we also have some tools that exist specifically to audition these changes in-place so we can make an evaluation of the effects of our workflow on the final result directly in the DAW or via an exported bounce. For instance Plugin-Allinace has ADPTR AUDIO Streamliner
And there are even free tools like the following site which says it helps you "Discover your music's Loudness Penalty score, for free": https://www.loudnesspenalty.com/
Here are some additional articles & quotes that can help clarify this issue further.
Best Mastering Level for Streaming
Mastering for Streaming Platforms: 3 Myths DemystifiedWhenever music gets distributed to Spotify, the audio is stored, cataloged, and then encoded with information with a program known as ReplayGain. This program either turns up or down the volume of the track to the default -14 LUFS, depending on how loud the master is in comparison to that benchmark.
Mastering audio for Soundcloud, iTunes, Spotify, Amazon Music and Youtube
[This older article from 2016 is included for chronological perspective. I'm not sure Spotify was using RG (Replay Gain) yet back then.]
As I am in the process of collecting & compiling this information here, this post will change and if these articles don't agree just understand that in the end we're creating standards based on human interpretations, tastes and opinions and the tools & science used simply support the current state of our ever-changing art in the music industry.
According to the middle article below, Amazon, Tidal and Youtube all use the BS.1770 [ITU-1770] standard. Testing of the same track as it appears on Amazon HD (lossless) and Tidal Lossless (with and without the individual player's normalization turned on) seems to show that both Amazon and Tidal use the same non-compression/limiting, indexed normalization. And their normalization algo's produced virtually identical results when tested from by a number of dynamic measures. (Spotify apparently currently uses RG but have committed to converting to BS.1770 in the future.) As expected, the internal dynamics [dynamic contour, if one will] remained effectively identical. When adjusted for level, the normalized tracks were indistinguishable from standard playback in ABX testing using blind-testing ABX tools.
ADDENDUM -- the second article linked above (3 Myths, Oct 2019) includes this specific info on platforms and their chosen normalization:
Next, let’s discuss the trickier matter of reference levels. Not only do all the services use different reference levels, many of them don’t even use the same normalization method. In fact, as of this writing, only Tidal, Amazon Music, and YouTube use BS.1770 (aka, LUFS). Others, such as Spotify, use ReplayGain (often with a modified reference level), while others still have developed their own normalization methods. Apple’s SoundCheck is a good example of the latter case.
To muddy the waters further, there’s nothing to prevent any of the streaming services from changing either their reference level, normalization method, or both down the road. In fact, Spotify has done this in the past. A few years ago they lowered their reference level by 3 dB. They have also stated that in the future they plan to use BS.1770, likely with a reference level of -14 LUFS integrated, but of course, that’s subject to change, and when this switch will take place is anybody’s guess.
Gearslutz also has a good post from about getting levels for the various platforms
Targeting Mastering Loudness for Streaming (LUFS, Spotify, YouTube)-Why NOT to do it.