7.4) Dynamic Compression
While the relative balance between sound effects should be relatively good, one challenge with a dynamically changing soundscape is that there’s no way to completely predict what the maximum or minimum volume levels for the combined mix will be. Depending on the gameplay and the various randomizations, circumstances could arise where the combination of all of the elements could create volume levels that are higher than what might have been seen when the files were playing in the Soundcaster Sessions. The concern is that some louder sound effects like explosions might overcome the other sound effects in the game or, worse, the combined levels of the sound effects and the music could distort the final output and push the signal sum over 0 dBFS. Inversely, there may be segments where the sound effects are very sparse and may not feel loud enough to support the gameplay.
In a Digital Audio Workstation, you can automate the volume of tracks at the precise points in the timeline where volume problems occur, but in a game there is no timeline. Therefore, conventional automation is not possible. Instead, you can insert a Dynamic Compressor across Audio Busses that can help you constrict the amount of volume change between the softer and louder sections of the soundscape and restrict the Dynamic Range of the mix. Because of the fact that your mix is a bit too dynamic to be consumed via headphones, Dynamic Compression might be a good solution.
Switch to Sync Group 2 in the Meter View.
In the Mixing Desk double-click the Sfx Bus header.
In the Property Editor, click the Effects Tab. (Pic01 Effects)
Click the Selector button for ID 0 and choose Wwise Compressor > New.
In the New Effect pop-up window, select your Default Work Unit for Effects, name your Effect and click OK. You’ve now inserted a Wwise Compressor Plug-in in the first insert slot of your Audio Bus. (Pic02 New Compressor)
At this moment, the selected new Preset leaves all of the levels on the Bus untouched, even if the signals start to get excessively loud, the Compressor will not begin to reduce the levels above a defined Volume Threshold until you say otherwise. In the next steps you are going to modify the Compressor settings so that the Dynamic Range is reduced by a small amount, meaning that you will set its Properties so it makes very loud sound effects like explosions a bit quieter and therefore making it possible to increase the overall Gain of the whole signal on the Audio Bus, making even the more quiet sound effects a bit louder and more noticeable.
Click the Edit button on the right of the Compressor row.
You can see that the Threshold is set to 0 dBFS, meaning that the Compressor will have no effect for all sounds below 0 dBFS. The Compression Ratio value can be thought of as a number over 1. With the default Compression value set to 1.5, it means that a 1.5 to 1 Compression Ratio is applied to sounds over 0 dBFS. This means for every 1.5 dBFS of levels over 0 dBFS, only 1 dBFS of actual increase in volume will be allowed. When Compressors are used with ratios of 10 to 1 or higher, they are commonly referred to as a Limiter, which is simply put a very aggressive Compressor. You even used one in an exercise of an earlier lesson. To hear the effect of the Compressor, lower the Threshold value so that it is actively compressing lower level signals.
Start the game and click Capture for a new Profiling Session to view current Input Levels on the Bus. (Pic03 Input Levels)
You can see that the overall level on the Sfx Audio Bus is quite loud, sometimes going right beyond 0 dBFS, which could result in nasty clipping artefacts in a player’s headphones or speaker system. Some sound effects are simply too loud, an explosion going right up to + 6dBFS, resulting in a distorted sound effect. This is where a compressor can come in handy.
Adjust the Threshold to -30 dBFS and the Ratio to 4. (Pic04 Threshold and Ratio)
This basically dictates that all signals that are louder than -30 dBFS will be decreased in their volume by a Ratio of 4:1. This is not a subtle change, but the resulting Compression shouldn’t sound too aggressive either. There are two more, very specific Properties of the Compressor, called Attack and Release. The Attack Time in seconds basically says how long a Compressor should wait before beginning to compress the signal after a signal has a level going over the Threshold of -30 dBFS. If you let the Compressor wait a bit, it results in the initial transient energy of the sound, meaning the very impact of the explosion, go uncompressed for a short time to make the compressed sound still pop/snap on bad listening equipment. It helps a sound effect not to get smushed by the Compressor. The Release Time in seconds basically says how long the Compressor should continue compressing a signal after its level has gone back below the Threshold of -30 dBFS. If you let the Compressor wait for too long to stop compressing the signal, it will make quieter sounds even more quiet, which in most cases is the exact opposite you want to achieve. You want to make it stop compressing very shortly after a loud signal has gone quiet again.
Set the Attack Time to about 0.3 seconds, the Release Time at around 0.1 seconds. (Pic05 Attack and Release)
Start the game and click Capture to view current Gain reduction on the Bus. (Pic06 Gain Reduction)
The picture shows the moment of a car exploding during gameplay. You can clearly see that there is an excessive amount of Gain reduction applied to it, 18 dBFS of Gain reduction to be precise. This is quite a lot. This will limit the Dynamic Range too drastically, which is quite noticeable.
Set a Threshold of -20 dBFS and a Ratio of 1.5 to decrease the volume going over the now higher Threshold value. Further increase the Attack Time to about 0.5 seconds. Now repeat starting the game and a new Capture to vie the updated Gain reduction. (Pic07 updated Gain Reduction)
You can see that at the same moment during gameplay, there is only a Gain reduction of 6 dBFS applied to loud signals. This is much better. Now, because the louder signals are being made quieter by the Compressor you could raise the overall level of the Audio Bus’s signal. You can do so by adjusting the Output gain Property of the Compressor.
Set the Output gain to an appropriate value, in case your Sfx are not loud enough. (Pic08 Output Gain)
Now, start the game one more time and click Capture not only for a Profiling Session, but also for the Loudness Meter in the bottom right of the Layout. (Pic09 Integrated Loudness and Loudness Range)
If you are mixing and trying to directly compare Loudness Level and Loudness Range of different runs in the Platformer game, you will have to recreate similar runs with the same length, since Loudness is measured over time. For example, if you are measuring the first run, then a second run where you continue measuring much longer after the run is already finished, the quieter soundscape of the highscore-screen could easily falsify the result of the second measurement and make it impossible to compare to the first measurement.
As you can see, the Integrated Loudness of a typical gameplay is still way above the Target Level of -23 LUFS. You will need to address this in your mix after the lesson. What looks promising is the value for the Loudness Range, which is now at around 9 LU for a typical gameplay scenario. If you compare it to before, you had a slightly higher value and therefore higher Dynamic Range, which for a headphones mix was a bit too high. With a subtle Dynamic Compression you fixed the problem and successfully reduced the Dynamic Range about -3 LU. Great!
Generate the SoundBanks to save your work and update the game.