How to create a Scatterer Instrument in Wwise

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When users migrate from FMOD to Wwise, the scatterer instrument is usually one of the most missed features. Let’s see how we can recreate its behaviour within Wwise but first, a quick overview at the instrument in FMOD (skip if you want).

FMOD’s Scatterer Instrument

This instrument essentially provides us with two handy features. On one hand, we can control how often sounds from a playlist will be triggered. This can be based on regular time or on musical tempo. On the other hand, we can also control the positioning each sound instance.

Spawning

We can control the spawn interval with a min and max spawn interval value. Additionally, we also have a spawn rate knob which is very handy if we want to automate the spawning rate with a game parameter. For example, we could have a scatterer instrument for birds chirping and the spawning rate is reduced as the weather gets worse.

Something to always keep in mind with spawning is that each element in our playlist will use a voice. A fast spawning rate plus a high polyphony can result in a lot of voices, specially if you have several scatterer instruments so keep in them in check if you have a limited voice budget which is usually the case for mobile or portable VR.

In world 3D vs full 2D

If you have a min/max distance that is not 0, FMOD will play the sounds around the emitter in a random position between the two values. Note that this positions are “in world”, as if they had they own emitters in the game world. This is very nice for things like birds around a tree or water splashes in a lake.

Now, keep in mind that even if you don’t have a spatializer on your event, having a non 0 min and max distance on a scatterer instrument will effectively make that event 3D. This is important to remember if (like me) you are playing your events through custom code and have checks for 2D/3D.

A different use case for a scatterer instrument is: what if we just want to play sounds around the listener in a “non in world”, 2D way? To do this, you would need to firstly not have a spatializer on the event which is probably already the case, if you were just creating a 2D ambience. Then, you need to set the min and max distance to 0. This will result in all sounds having the same volume and pan but that can be easily fixed by just randomizing this values. In fact, the scatterer instrument already has a “Vol Rnd” knob that you can use for this.. To change the panorama, you will need an extra effect on the track or you can also randomize the event panner if you want to affect everything at once.

Recreating voice spawning in Wwise

Firstly, we need to create a random container with all the Sound SFXs or other containers that we want to use. By default, a random container just plays one of its items following whatever randomization settings you have. So each time an event tries to play the container, we would just get one sound or voice. We can change this by changing the Play Mode from “Step” to “Continuous”. Now our container will try to play the complete list of objects we have. We can then make this loop so we cycle randomly through the list without ever stopping.

To control how often the sounds play, activate “Transitions” and choose “Trigger rate”. This allow us to control how often sounds are spawned in a similar way as in FMOD. You may want to randomize the duration value so sounds don’t play at a predictable rate.

On the example above, you can see that sounds will spawn at a rate between 0.5 and 2 seconds. We now have an easy way to control how often we spawn sounds. Of course, we would need to probably create an stopping event if we want to stop our sounds spawning at some point. Now we just need to figure out how to play these sounds around the game world.

Managing 2D/3D positioning in Wwise

In the positioning tab, under the 3D position section, we can find three different modes:

  • Emitter: This will make the position always the same (the position from which we have played the event). Use this if you don’t want any movement at all.

  • Emitter with Automation: This will take this same emitter position and add some movement that we can control. Use this if you want the sounds to be played in world, around the emitter. This will use whatever attenuation values you have set. You can even set paths with movement (think birds flying around). This will achieve the same effect as playing an FMOD 3D event with an scatterer instrument with a non 0 min and max distance.

  • Listener with Automation: Same as above but the sounds play around the listener. Make sure to tick “Hold Listener Orientation” if you want the sound to be completely 2D and thus independent on the listener movement. This means the sounds won’t feel like they come from an specific point in the world but a predetermined position in the panorama. Your attenuation settings will be respected though. Use this for purely 2D ambiences. This will be same effect as an FMOD scatterer instrument with 0 min and max distance and no spatializer.

When setting the 3D position automation, make sure you choose “Step“ so each time a sound spawns, a different path is chosen. You can also use “Random” if you want the position to change in a non predictable way.

In conclusion

After using both middleware I went from “is a shame Wwise doesn’t have a scatterer instrument kind of container” to “Wwise can re-create all the scatterer behaviour and even make it better!” so there’s that. Let me know how it works for you and if you find any issues yourself.