But what about the GPL source code requiring the Steinberg code in order to be compiled? The software doesn't seem so "free" in that case. Besides, Steinberg could at any point cease to distribute anything related to the VST SDK. (Theoretical of course, but still a possibility.) The software that was supposed to be free to be modified and fixed would no longer be so, because it couldn't be compiled. I strongly believe this could be considered a GPL violation by the Free Software Foundation.