[Joonas] became frustrated with cheap but crappy MIDI to USB converters, and the better commercial ones were beyond his budget. He used a Teensy LC to build one for himself and it did the job ...

He solved the problem by building the Tannin DIY MIDI controller ... to a PC via serial over USB. On the host PC side, he ran loopbe30 to create a virtual MIDI cable to Traktor, his DJ software.