Implement audio normalization using BASS

[smallketchup82]

Closes #1600

Prereqs:

• Update BASS libraries and add BASSLoud osu-framework#6233
• Add support for Volume FX and BASSLoud peppy/ManagedBass#1
• Add TrackLoudness (BASSloud) osu-framework#6281

Audio Normalization

Audio Normalization is the process of determining the loudness of audio and standardizing (normalizing) it to a set level. If you normalize a number of audio files to the same level, they will all sound the same volume wise. Normalization is useful for making sure that loud songs get made quieter so that they aren't so loud, and quiet songs get made louder so that they aren't so quiet. This reduces the number of times you will need to change your volume, and yes, it means you can finally play The Big Black without having your eardrums reduced to shreds.

Here's a video showing what Audio Normalization looks like in osu!. In the video, all 3 of my volume sliders are set to max. The beatmap songs are being normalized to -14 LUFS. Try to focus on how every song sounds volume wise, you should find that they all sound about the same in terms of volume no matter the instruments in the song. I find that tech maps work the best when trying to tell what normalization does

normalization.mp4

Description of Approach

So, I decided to take a different approach than the old PR. The old PR tried implementing the algorithm manually which isn't good since we'd have to manually maintain it. This PR uses BASSLoud which is maintained by BASS and will get regular updates. I also noticed a lot of missing things in the old PR, such as recalculating the normalization values in the background. I've taken more or less the same structure as the old PR but improved upon it heavily.

When talking about approach in terms of normalization, this implementation calculates loudness using the ITU-R BS.1770-4 standard, but normalizes to -14 LUFS instead. I've spent a couple hours playing the game on my branch to get a feel for the normalization, and I've found -14 LUFS to best meet my expectations. It makes the audio not too quiet, where the effects are really loud, but also loud enough that 100% volume actually feels like 100% volume. Additionally, -14 LUFS is what Youtube & Spotify normalize to, so I believe that it's probably the best level to normalize to when it comes to music. Whereas -23, as recommended by EBU, is best for movies and TV programmes.

My PR uses Integrated Loudness, meaning the average loudness across the entire song. This is different from more conventional methods of loudness detection, such as True Peak, which normalizes based on the peaks (parts which are loudest) in the song. Integrated Loudness is known for working better than True Peak since it takes into account how the song sounds like. Meaning sudden sounds in a song (say sfx), a sudden increase in vocal volume (such as in a chorus), or a sudden increase in the volume of an instrument (say at the end of a song as a finisher), will not be accounted for. These sudden sounds will not influence how the song is normalized, and won't be the reason for a relatively quiet but suddenly loud song to be made more quiet because of that sudden section. The old pr seemed to calculate and use a variety of methods, including True Peak, which was completely unnecessary.

Description of Changes

This PR adds the ability for osu! to normalize audio tracks to a target level using BassLoud. This implementation goes through realm and tries to find maps which do not have loudness detection values stored, it then calculates these values via a background process. Once these values are calculated, they are stored and cached in Realm. These values are grabbed if they exist when a beatmap's audio track is loaded, if they don't exist, the old global audio reduction is applied (0.8). The values are used to create a Volume Fx filter for the track to normalize it.

Changes to Realm

Since we're now tracking Audio Normalization values in Realm, we need to bump the version otherwise a migration error is thrown. Apart from creating object mappings, the only change to realm here is a bump to the version.

Future tasks

I left a lot of quality of life features I wanted to implement out of this PR. This PR is already big as is and I don't want to add to it with qol features. I'll be listing these features and working on adding them in the future

• Make a new PR to normalize/do something with hitsounds
• Make a new PR to normalize effects
• Investigate making a setting to toggle this
  • Doesn't seem too necessary. This doesn't make that big of a change where users would need/want to disable it. The volume sliders still work and the user can adjust them to match their taste.
• Investigate adding a button to the debug section to purge and regenerate the loudness values

Testing

Testing this is a bit difficult since there are many changes in many areas. First things first, clone the osu branch in this PR. Next, clone my ManagedBass branch. When you've done this, pack the following projects into nuget packages: BassLoud, BassFx, and Bass. Go back to osu.Game and create a new nuget source pointing to the folder(s) where these .nupkg's are stored. Install them over the current versions. Then clone my osu-framework branch. Here you should pack NativeLibs, add a source for it in osu.Game, then install it over the current NativeLibs package. Then, clone this branch as osu-framework. Use the useLocalFramework scripts to add it to osu.Game. After doing all of this, you should be able to build and run osu! with audio normalization. This process will get exponentially easier once the prerequisites (or at least the ManagedBass side of things) get merged.

Feel free to ping me in the #osu channel of the osu!dev discord if you need help with this.

Final remarks (notes before reviewing)

Please read this section before reviewing

• Please backup your realm file before testing!
• Please go through this commit by commit. I leave a lot of useful information in my commit descriptions. Start at 7a3ccf3
  • Sorry about the commits before that one, I tend not to think about variable names in rough drafts and poc code
• I intentionally left out tests since this isn't really something you can just slap in a test. It works and tests best when using the full client and playing around with it
• The version numbers have been changed since I changed them to be able to test this locally. I will likely revert those
  changes somewhere down the line
• I'll fix up the imports, references, and all of those once the prerequisite PR's get merged
  • I might make my own nuget packages and update the references to use those so that people can test this while the prerequisites are being merged

Developed with help from @hwsmm (thanks!)

[mcendu]

Haven't tested this branch, just nitpicking from a read. This is a nice feature I am looking forward to.

[smallketchup82]

Quick update:
Please don't review/merge this right now as I'm in the process of reviewing smallketchup82#1

[smallketchup82]

Finished reviewing the new implementation myself. This should be in an acceptable state for review from the core team.

I want to raise some concerns, however:

• This new implementation, while significantly simplifying things, also adds a new setting to normalize audio. We weren't sure whether to keep that in, but it was easy enough to implement that we figured why not. I also wanted some input on Improvements for audio normalization smallketchup82/osu#1 (comment). The original implementation of this new implementation bound hitsound volume adjustment to the beatmap hitsounds setting. Meaning that the volume offset would only be applied to hitsounds if the beatmap hitsounds setting was turned on. I've decided to remove that since, to me, it didn't seem correct. But I want to let the core team call that shot. If keeping that implementation is preferred, it can be added back in.
• The volume ceiling is... iffy. -14 LUFS makes 100% volume pleasant to listen to, but at the same time, it causes a couple of issues. A lot of players prefer their hitsounds to be louder than the music. Since 100% master volume is already at a level which is considered good/loud enough for your ears, setting music to 50% makes it really quiet.
  • My original idea to fix this was adding another setting called "volume boost" which would increase the target level from -14 to something like -10, allowing the user to increase the maximum output volume of lazer, and therefore enable them to adjust effects and music volume without it being really quiet
  • At the same time, we can just leave this as is, since there's already a setting baked in to disable normalization.
• As stated in the new implementation's PR, a fallback volume reduction of 0.8 doesn't really match well with -14 LUFS. Turning normalization off results in your ears begging for mercy. A better value for the fallback volume reduction should probably be found.

[smallketchup82]

Here's an updated video demonstrating normalization in various different scenarios (since its rather hard to test, I figured making this video would be useful to an extent). I would highly recommend making sure that your system volume is at a comfortable level, then watching the video at maximum volume (for the video, not system). This is to give you a feel of what -14 LUFS actually feels like, and what the global reduction feels like in comparison.

I threw it together in 20 minutes in premiere pro, so the quality is horrible (sorry lol)

Audio.Normalization.Demo.reencoded.mp4

[nekodex]

Lemme just state up front that I've not looked at or reviewed the code, so take that into account when reading my feedback.

I also wanted some input on Improvements for audio normalization smallketchup82/osu#1 (comment). The original implementation of this new implementation bound hitsound volume adjustment to the beatmap hitsounds setting. Meaning that the volume offset would only be applied to hitsounds if the beatmap hitsounds setting was turned on. I've decided to remove that since, to me, it didn't seem correct. But I want to let the core team call that shot. If keeping that implementation is preferred, it can be added back in.

Hmm after giving this some more thought, I'm not 100% sure.

My initial gut reaction says that maybe the volume adjustments should only apply to beatmap hitsounds (i.e. mapper/custom hitsounds included with beatmaps)? But on the other hand, if a beatmap was created with legacy/lazer hitsounds in mind, then we'd want those to be adjusted too. As the linked comment brings up, it might be a bit weird for hitsounds to change volume between beatmaps, but I think maybe that's fine?

Maybe @ppy can provide a second opinion?

This also begs the question as to what happens if someone maps on lazer with normalization on and then a player plays with normalization off... or vice-versa. I don't really have an answer to this.

• The noise ceiling is... iffy. -14 LUFS makes 100% volume pleasant to listen to, but at the same time, it causes a couple of issues. A lot of players prefer their hitsounds to be louder than the music. Since 100% master volume is already at a level which is considered good/loud enough for your ears, setting music to 50% makes it really quiet.

Does this PR also remove lazer's current hard-coded global volume reduction? If not, that might be what's making things too quiet. I'm also not sure what curve the volume controls currently use, but we could potentially change that if it's ramping volume down too fast?

• My original idea to fix this was adding another setting called "volume boost" which would increase the target level from -14 to something like -10, allowing the user to increase the maximum output volume of lazer, and therefore enable them to adjust effects and music volume without it being really quiet

I don't know how the rest of the team feels about adding more user preferences, but we could do something similar to what Spotify has and include a dropdown to choose between Loud (-11dB LUFS), Normal (-14dB LUFS) and Quiet (-19dB LUFS) normalization options.

Alternatively, we could just outright normalize to a louder level and lower the global music volume by default, allowing players to turn the music volume up if they desire - similar to how (I believe) the master volume control works now?

It's also probably worth mentioning that some players have complained in the past when we've added volume reductions to lazer, as their computer setups aren't able to increase the output volume enough otherwise, for whatever reasons. Thus normalizing to a louder level and reducing via the global volume controls might be the preferable choice if we don't want players just reactionarily disabling normalization.

This might bring the risk of the mixed output going over 0dB and/or clipping, but ideally in the future everything will be running through a global compressor/limiter anyway to prevent this.

• As stated in the new implementation's PR, a fallback volume reduction of 0.8 doesn't really match well with -14 LUFS. Turning normalization off results in your ears begging for mercy. A better value for the fallback volume reduction should probably be found.

I think it's probably fine for the volume to jump up when normalization is disabled - it's common behaviour with music players. If it's that much of a volume jump, we could maybe bump the global master or music volumes down by some amount when normalization is disabled to alleviate it somewhat, but still allow players to undo the reduction if they wish.

[smallketchup82]

it might be a bit weird for hitsounds to change volume between beatmaps

My thoughts on that is that hitsounds will likely be changing in volume regardless. As peppy said in our discussion in the osu!dev discord, mappers will typically try to psuedo-normalize hitsounds to the volume of the track themselves by setting every hitobject to a certain volume. I think that adjusting the volume offset for hitsounds regardless of whether beatmap hitsounds are on or off is probably the correct way to go about it, at least to me, since the goal is to retain the relationship between the track and the hitsounds, and only doing that in certain circumstances sounds counter-intuitive and unexpected. Though, it's probably a question that we'd want more opinions on.

Does this PR also remove lazer's current hard-coded global volume reduction?

Yes, but I don't think it removes the volume reduction when first starting the game from a fresh install.

I don't know how the rest of the team feels about adding more user preferences, but we could do something similar to what Spotify has and include a dropdown to choose between Loud (-11dB LUFS), Normal (-14dB LUFS) and Quiet (-19dB LUFS) normalization options.

When compared to the option of normalizing to a louder level but setting the default volume to a lower level, like 50%. I find myself siding more with the dropdown approach (mostly from personal preference, no real basis for it). But to be honest, either approach would work well and would be easy to implement. I'm pretty indecisive on this so I think it might be something that we'd want more opinions on, or to poll somewhere (in a discussion, osu!dev discord, idk).

if we don't want players just reactionarily disabling normalization.

Honestly, when its put that way, it kinda makes me want to reconsider adding the ability to enable or disable normalization. I believe that normalization should be on for most players unless there's a very good reason not to, since the pros of normalization outweigh the cons. I'm also sorta indecisive on this.

I think it's probably fine for the volume to jump up when normalization is disabled

After reading your thoughts on this, I think that I'll just keep it as is. While reducing the volume globally to get it to be close to -14 LUFS would be nice, I realized that players probably wouldn't like not being able to revert the normalization changes themselves (they would expect volume to be similar to before normalization was implemented if they disable normalization).

Thanks for your thoughts! I'd definitely like to get some more opinions on those concerns, minus the 3rd one cause I'm probably just going to leave it alone.