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Hi All,

I’m seeing some behaviour with polyphony that makes me think I don’t understand it. :)

I have an FMOD Event in a Unreal level, which auto activates. If I make several of these FMOD Events and play the Unreal project, I hear the sound playing for as many copies of the event there are in the level.

Now, this would by default be expected behaviour, however (and this is where I am confused) the FMOD Event in question has its polyphony set to 1.

The manual states:

“The Polyphony Property defines the number of instances of a particular Sound Module that can be voiced simultaneously. So if set to a value of 1, the target Sound Module only ever has a single instance of it played at the same time.”

So my questions are:

  • Is the behaviour I am seeing correct?

  • How do we define ‘instances’ here – is the same FMOD event copied
    several times seen as multiple instances?

  • What is the best way to handle polyphony across multiple copies of
    an FMOD event in Unreal?

I have a test Unreal and FMOD project which reproduces the behaviour, they can be accessed here:

Link to projects

Repro steps:
1) Load Unreal Project in Unreal 4.16.2.
2) Load FMOD Project in FMOD 1.09.06
3) Observe ‘Polyphony Test’ event in FMOD project with volume of -12dB.
4) Observe ‘Polyphony_Test’ object copied multiple times in the Unreal level.
5) Press play on Unreal level.

Results
The test sound event can be heard playing at a loud volume, despite it being at -12dB, due to it playing multiple instances of it.

Expected Results
Only one instance of the test sound to play because the event’s polyphony is set to 1.

Many thanks in advance! :)

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Great Answer
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The behavior you describe is exactly what’s expected: The polyphony of a sound module only applies within the event instance. As such, each separate instance of an event may play a number of simultaneous sound module instances equal to the polyphony limit of that sound module.

The text in the FMOD Studio User Manual is incorrect. Thanks for reporting this issue! Fortunately, we’ve already written an updated version of the manual that contains a large number of corrections and changes, and this new version of the manual will be included in an upcoming release of FMOD Studio.

In any case, if your goal is to limit the number of instances of an event that can play simultaneously, you should set the event’s Max Instances property. This property is found in the event macro controls, which are displayed at the right end of the deck when the event’s master track is selected.

  • Jacob Almond

    Haha, thank you! I knew it would be something simple. I laughed when I read the bit about limiting the number of instances by using Max Instances! ?

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