\begin{tikzpicture}
\begin{axis}[
axis x line = bottom, axis y line=middle,
enlargelimits = upper, clip=true,
scale only axis,
axis line style={->,>=stealth, shorten >= 0pt},
xlabel={$\omega$},
ylabel={dB},
every axis x label/.style={
	at={(ticklabel* cs:1)},
	xshift=-0.2cm,
	anchor=north,
},
every axis y label/.style={
	at={(ticklabel* cs:1)},
	xshift=0.4cm,
	anchor=south,
},
every outer x axis line/.append style={white!15!black},
every x tick label/.append style={font=\color{white!15!black}},
xmin=0, xmax=1,
ymin=-100, ymax=0,
xtick={0, 0.25, 0.5, 0.75, 1},
xticklabels ={$0$, $\pi/4$, $\pi/2$, $3\pi/4$, $\pi$},
ymajorgrids,
every outer y axis line/.append style={white!15!black},
every y tick label/.append style={font=\color{white!15!black}},
legend style={draw=white!15!black,fill=white,legend cell align=left, at={(axis cs: 1.05, -5)}}]

\addplot [smooth, color=blue2, solid, line width=2pt] table[x index=0,y index=3] {figs/data/kaiser_spectrum.dat}; \addlegendentry{$\beta = 0$};
\addplot [smooth, color=red2, solid, line width=2pt] table[x index=0,y index=2] {figs/data/kaiser_spectrum.dat}; \addlegendentry{$\beta = 3$};
\addplot [smooth, color=green2, solid, line width=2pt] table[x index=0,y index=1] {figs/data/kaiser_spectrum.dat}; \addlegendentry{$\beta = 6$};
\end{axis}
\end{tikzpicture}