set terminal wxt
set terminal wxt font "/Library/Fonts/Sans Serif, 11"
set multiplot
set size 1.0,0.5
set datafile separator ";"
set xlabel "freq. [Hz]"
set origin 0.0,0.0
plot "spectrum.csv" using 1:2 title "Amplitude" with lines
set origin 0.0,0.5
plot "spectrum.csv" using 1:3 lt 3 title "Phase" with lines
unset multiplot

set output "spectrum.png"
set terminal png font "/Library/Fonts/Sans Serif, 11"
set multiplot
set size 1.0,0.5
set datafile separator ";"
set xlabel "freq. [Hz]"
set origin 0.0,0.0
plot "spectrum.csv" using 1:2 title "Amplitude" with lines
set origin 0.0,0.5
plot "spectrum.csv" using 1:3 lt 3 title "Phase" with lines
replot