% \xin, \yout, and \Hz must be defined before calling this script
\begin{tikzpicture}[->, >=stealth, shorten >= 0pt, draw=black!50, node distance=3.2cm, font=\sffamily]
\tikzstyle{node}=[circle,fill=black,minimum size=2pt,inner sep=0pt]
\tikzstyle{block}=[draw=black,rectangle,fill=none,minimum size=1.5cm, inner sep=0pt]

\node[node] (xc) {};
\node[block, right=1cm of xc, text width = 2cm, align= center] (DSP) {\Hz};
\coordinate[right=1cm of DSP] (yc) {};

\path (xc) edge (DSP);
\path (DSP) edge (yc);

\node[above = 0mm of xc, text width = 1cm, align=center] {\xin};
\node[above = 0mm of yc, text width = 1cm, align=center] {\yout}; 
\end{tikzpicture}