set term png

set output "kadai2-1dft.png"

fs = 16000.0
N_fft = 512.0

set xlabel "Frequency [kHz]"
set ylabel "Amplitude"

set xrange [0:8]
set grid

plot "sample01_dft.txt" using ($0 * fs / N_fft / 1000):1 \
    with lines notitle