7.5 Side-Chaining


7.5) Side-Chaining



Now with all sound effects sitting pretty good level-wise within your soundscape, the volume of the Music Track seems a little too quiet to be exciting enough. The only problem is that making it louder will make sound effects more likely to be overheard and inaudible due to the greater level of the music, or make the mix too dense and intransparent. So wouldn’t it be nice if you could make the music louder on a general level, and as soon as important sound effects are being played, the Music gets quieter to give some room to the sound effects?

You might first think of Ducking, used in an earlier lesson to make the Atmo and Vehicles Busses’ Volume quieter whenever there is a signal on the Destructables Audio Bus. But the approach you are going to use to fix this is what’s referred to as Side-Chaining, which is a much more sophisticated method to get such a result. This term is associated with classic analog audio systems where the audio signal from one channel is split off and fed to another channel to be used as a source signal that can be used to modify a Property of that channel, such as Volume. Wwise doesn’t display specific Side-Chaining features in the user interface, but you can easily build the same result by using a unique feature that allows Wwise’s Audio Meters to generate a Game Parameter–RTPC, which can then be mapped to nearly any Property of any Object, such as the Volume of the Music Audio Bus. This approach offers immense flexibility that goes far beyond the type of control that is offered with conventional Ducking features.

Pic01 New Meter Plug-in

Pic02 Observing Meters

Pic03 Release Time

Pic04 Meter Max Range

Pic05 New RTPC

Pic06 Side-Chaining Range

Pic07 RTPC Tab

Pic08 Bus Volume Curve

Pic09 Soundcaster Testing

  1. Before you start, make the Music Bus Volume a bit louder, say between +6 an +9 dBFS.

  2. Play the game to see if the music volume feels right and gets you excited when playing.

    Now as you might have noticed with the music getting louder, the mix with all the sound effects gets very dense and lacks transparency. When doing a mix, density and transparency is always a balance act, that demands quite some experience from the Mixing Engineer. You’re going to use the Fx Bus Volume for Side-Chaining the Music Bus.

  3. First add the previously created Wwise Gain Plugin to the third insert slot on the Fx Audio Bus in the Effects Tab. As discussed earlier, this is necessary for the Audio Meter to show up on the Bus.

  4. Then add a new Wwise Meter Plug-in on first insert slot. Click on the Default Work Unit, choose a name and click OK. (Pic01 New Meter Plug-in)

  5. Click the Edit … button right next to the Effects Plug-in.

  6. Turn on Start Capture and then play one Object from the Soundcaster View that has its Output set to the Fx Audio Bus. Observe the Meters. (Pic02 Observing Meters)

    The In and Out Meters are the most dominant display in the Effect Editor. The In Meter represents the actual signal, but the Out Meter represents a value that can be sent as an RTPC. A note at the bottom indicates that this Meter will only be active if a Capture is active. You see how the Output Meter moves in similar to the Input Meter; however, there is only one Graph for the Output Meter, compared to the stereo Input Meter. This is because the Output value is based on a sum of the channels on the Audio Bus.

    Currently, the Output Meter reacts instantly to changes in the source signal; however, similar to an RTPC’s Slew Rate, you can change the Output Meter’s ballistics to respond differently, smoothing the response of the output signal. This will be useful when this value is used to affect the Music Bus: the changes will be less abrupt.

  7. Repeat starting a Capture and playing the Object again. Experiment with different Release values and end with a value of about 0.5 seconds for starters. Notice that as the signal on the input is decreasing, there is still a good amount of signal being displayed in the Out Meter. This is the result of setting a Release Time, which further holds the input’s signal in the output for 0.5 seconds longer, before it is being released. This is basically the same when using a Dynamic Compressor. (Pic03 Release Time)

    You may have noticed that the highest level on the Out Meter Range is different than the highest level on the In Meter Range. The Out Meter Range is determined by the Output Game Parameter area’s Min and Max values. This allows you to scale the Output Range of values to a different set of values. In this case, you’ll change the Max range to 6, so there’s a one to one relationship between the Busses actual Meter Level and the Output value.

  8. Set the Max Value to 6 dBFS. (Pic04 Meter Max Range)

    Now that you have the Meter Output responding and generating the values you want, you now need to attach the Meter to an RTPC. In this case, you’ll create a new RTPC specifically representing the value for Side-Chaining.

  9. In the Output Game Parameter group box, click the Selector button and choose New. Select the Default Work Unit where you can find all other RTPCs, choose a name and click OK. (Pic05 New RTPC) It’s important that the RTPC’s value range matches that of the Meter’s output range.

  10. Double-click the Sidechain Game Parameter. You also have to add a Default value, which in this case should assume that the Fx Bus is not active.

  11. Set the RTPC’s Min value to -48 dBFS, the Max value to 6 dBFS and the Default value to the lower level of -48 dBFS. You get a message indicating that values will be stretched, which is okay because you haven’t used the RTPC in a Graph with set Control Points yet. (Pic06 Side-Chaining Range)

    Now you’re ready to attach the RTPC to the Volume Property of the Music Audio Bus. You can close the Property and Effect Editor Views, stop the Capture if it is still active and go to the Designer Layout.

  12. Open the RTPC Tab of the Music Bus.

  13. Click the Selector button and choose Bus Volume. Click the Selector button for the X Axis and choose the Game Parameter you just created. (Pic07 RTPC Tab)

    Now, you want the Bus Volume of the Music Bus to get gradually lower as the Side-Chaining value that represents the Volume of the Fx Bus increases. You can test the right Curve during gameplay or a Soundcaster simulation.

  14. You could end up with something like this. As the Fx Bus Volume increases, the Music Bus Volume is gradually brought down to a maximum amount of -6 dBFS. This should make room for sound effects and let them cut through the music a bit better. (Pic08 Bus Volume Curve)

  15. Test the Side-Chaining of your game’s music and adjust the Properties to your liking. (Pic09 Soundcaster Testing)

  16. After completion, Generate the SoundBanks to save your work and update the game.