Merge branch 'master' of https://github.com/vhcd/vhcd.github.io

_posts/2024-04-01-buttkicker.md

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+---
+published: true
+title: 'Buttkicker + Unreal Engine'
+image: 'uebk.png'
+---
+
+Want to use a [Buttkicker](https://thebuttkicker.com/) in an Unreal Engine project? There are many ways to go about it, so let's cover a few.
+
+# What's a Buttkicker?
+
+You can think of it as a "shaky subwoofer on steroids". It's a device used in the simulation community (e.g., plane, racing) to increase immersion by adding vibration to the cockpit.
+
+[![](/images/bksim.png)][0]
+<center><i>Source: FPZERO Simulators</i></center>
+
+# Problem
+
+The effect's strength is derived from the audio signal, which has its advantages but also drawbacks. In our case, the main issue is that we want to control the vibration independently of the simulation sound; for example we might want to have some feedback from the device even when no sound is being played.
+
+So let's explore the solutions to control our Buttkicker outside of the main audio channels.
+
+# Solutions
+
+## Use the Buttkicker SDK
+
+Well, it doesn't exist, so... The amplifier has a USB input, which gave me some hopes that their would be some SDK with that; but no, it's just an audio device.
+
+## Use an external sound adapter...
+
+Since an audio signal is the only way to control the Buttkicker, and since we also want to control it seperately from our main audio, a straightforward solution could be to use a second audio adapter on the computer (like [this one][1]) dedicated to the device. Then we would just have to send specific audio signal to this adapter to control the Buttkicker.
+
+[![](/images/audio_adapter.png#center)][1]
+
+### ... in Unreal
+
+Let's do that in Unreal! Well, vanilla Unreal doesn't really handle multiple audio output devices. And by that, I mean it definitely doesn't. I dove into the source code (which I just love be able to do), and saw that both [`FMixerDevice`](https://github.com/EpicGames/UnrealEngine/blob/5.3/Engine/Source/Runtime/AudioMixer/Public/AudioMixerDevice.h) and the Windows interface [`FMixerPlatformXAudio`](https://github.com/EpicGames/UnrealEngine/blob/5.3/Engine/Source/Runtime/Windows/AudioMixerXAudio2/Private/AudioMixerPlatformXAudio2.h) very much expect only one device being used at a time.
+
+However, we could explore other audio interfaces within Unreal. I'm guessing [Wwise](https://www.audiokinetic.com/en/products/wwise/) can do that, and [SDL](https://www.libsdl.org/) probably too. I didn't explore any of those solution further, as it was beyond my very low motivation threshold for this project.
+
+### ... outside Unreal
+
+[Python](https://www.python.org/) is [pretty cool](https://xkcd.com/353/), you know? There's a lib for everything, including, [playing sound](https://python-sounddevice.readthedocs.io/) on [any device](https://python-sounddevice.readthedocs.io/en/latest/usage.html#device-selection).
+
+So we implemented the following:
+* On Unreal's side, send whatever information we want to use as variable for the Buttkicker. We used [ZeroMQ](https://zeromq.org/) ([Unreal plugin](https://github.com/hdhauk/UnrealZeroMQ)) because we like it, but TCP or UDP would also work as well.
+* On Python's side, we continuously [play a signal](https://python-sounddevice.readthedocs.io/en/0.4.6/examples.html#play-a-sine-signal) modulated according to the data received. All that just on the dedicated Buttkicker audio adapter, of course.
+
+And it works great! A bit too complex for my taste though...
+
+## Use MetaSound
+
+Even though the "two audio adapters" solution works fine, I wanted to try to find something less complex, ideally that doesn't require either special hardware or external software.
+
+[MetaSound](https://docs.unrealengine.com/5.3/en-US/metasounds-the-next-generation-sound-sources-in-unreal-engine/), Unreal's new sound system, allows us to output sound to [any audio channel](https://docs.unrealengine.com/5.3/en-US/metasounds-reference-guide-in-unreal-engine/) we want. So let's imagine that I...
+* Am using a Stereo sound system (actual non-Buttkicker sound)
+* Plug the Buttkicker to the Rear output on my sound adapter
+* Tell Windows that I'm instead using a Quad sound system
+* Use a MetaSound Source to only output on the Rear channels
+* Vary said sound according to whatever variable in the simulation
+
+Would that work? Yes it does! 
+
+![](/images/metasound_bk.png)
+
+It has some limitations though. Notably: even if the "Buttkicker" sound is not played on the main audio device, the inverse is not true: the main audio sound is played on the Buttkicker. So if a loud sound plays on the Stereo system, it will produce vibration on the device.
+
+The Buttkicker amplifier comes with a frequency cutoff option, so at least we can filter out most sounds from producing effects.
+
+Another limititation is that it doesn't scale up to a 7.1 sound system: at this point, you don't have any leftover output that you can allocate to the Buttkicker.
+
+# Conclusion
+
+We're still not sure which solution we'll end up going with. The Python script works perfectly, but the added layers of complexity don't sit well with me. The MetaSound on the other end is very simple, but we'll have to run more tests to see if the real audio leaking  over to the Buttkicker becomes an issue or not.
+
+[0]: https://www.fpzero.co.uk/blog/buttkickers-what-are-the-benefits/
+[1]: https://www.startech.com/en-us/cards-adapters/icusbaudiob