Ok, there's an easier way to change tuning. That "tune" parameter is just an offset in octaves, so what you could do is add 0.25 to its values to retune it from A to C (+ 3 / 12 semitones). If you want to tune octave down, substract 1 from that. So -0.75 would retune it from A to C an octave below.
tune = hslider("Tune[OWL:D]", -0.75, -0.85, -0.65, 0.0001);
freq = sample2hertz(tune);