The Internet of Things (IoT) is fostering advancements in the embedded systems world, widening the range of available single-board computers and lowering their price. The Internet of Musical Things (IoMusT), the IoT musical counterpart, is thriving as well with more and more examples of embedded devices useful to build connected musical interfaces. For this purpose, real-time architectures based on the Linux operating system are increasingly used. In this paper, we compare two radically different approaches to real-time Linux audio: one system is based on the PREEMPT RT patch and the ALSA framework and the other on the Xenomai patch and the Elk Audio OS. Our study aims at providing audio developers working on IoMusT devices and applications with a clear quantitative picture of how these two systems compare. Our results reveal that Xenomai provides lower audio round-trip latency, lower scheduling latency, and manages to exploit more CPU performance at a given latency setting while guaranteeing perfect audio quality. Nevertheless, PREEMPT RT still delivers good performance, and it is widely supported resulting in a more accessible alternative. All the tests have been carried out on the Raspberry Pi 4B single-board computer combined with the HiFiBerry expansion HAT.
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