Strange CPU spikes from convolution reverb

Hello, what are these CPU spikes on Master bus that are visible on this pic from profiler?
The red part is the Convolution reverb and the yellow part is when i bypassed it and inserted a “regular” fmod reverb. Is this normal behaviour for conv?
Thank you

The convolution reverb is significantly more expensive to use than the standard FMOD Reverb, so it is expected to see a difference in CPU usage. The performance also depends on the IR file used - longer IR files and ones with more channels will use up more CPU.

Spikes like what you are seeing aren’t to be expected, however. Can you provide some more information:

  1. What platform are you on?
  2. What IR file are you using (file size, length, channel count, etc. If possible to share that would make reproducing this issue easier)
  3. How many convolution reverbs are in play at once? Is this one convolution reverb in a group bus or are these placed on individual events?


  1. I am on Windows and building for Windows
  2. IR File is 2sec long, 6 channels, 48Khz, 16bit, i will upload it here
  3. At the time of the test 1 convolution was playing.

Reverb is inserted on the return bus and sent from sfx bus using sends,

Here is the file:

Thank you

Thanks for sharing the IR file. I’ve been able to reproduce the problem and sent it over to our dev team to investigate further.

Thats great, thanks. Looking forward to see whats up.

It seems that the convolution reverb has some performance issues, particularly when there’s some upmixing and/or downmixing involved. We will be looking into improving this performance for a future release.

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Hello, any news on this issue?

It’s still in our backlog and we don’t have a fixed date for when it will be looked at as it’s a bit complicated. Please keep an eye on future releases.

Hi Koca,
I’m working on this issue now


Great, thanks for the update.

If the Convolution Reverb goes through an optimization pass, could this optimization be integrated to older versions of FMOD Studio (1.10.x) as well?

It will be going into the new 2.01 performance branch, but for custom requests of this nature, they can be done via a support agreement at

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So it will be out five minor versions from now?
And share some info about what you found and fixed and what can we expect from Conv Rev after this.
Thank you