@resynth it was a while ago when I was playing with this... so my memory is not perfectly clear.
however, I seem to remember the 'issue' I had with qlib was the frequency range was a bit limited.
iirc, when I asked about it, they said indeed it was designed for guitar/voice (?) and that it might not be suitable for other frequencies and sources.
(I was trying to use it as a tuner, and it was not anywhere near reliable over a decent range for that, even with a sine wave)