Variation of the cutoff frequency with height in the quiet-Sun models VALC (panel a), FALC (panel b), and Avrett2015QS (panel c). The lines with asterisks show the cutoff values determined from the examination of the phase-difference spectra in a numerical simulation with a vertical magnetic field of 5 G (black) and 300 G (red). Color lines indicate the analytical cutoff frequency computed using Eq. (1) (blue line), Eq. (2) (green line), Eq. (3) (violet line), Eq. (4) with 5 G magnetic field strength (black line), and Eq. (4) with 300 G magnetic field strength (red line). The vertical dashed lines mark the height where the plasma-β is unity for the models with a field strength of 5 G (black) and 300 G (red).