Block with two inputs in pgf/TikZ

Question

I am trying to draw the following block diagram using pgf/TikZ. Actually I am struck at getting the two inputs to the first block horizontal.

What is the best way to draw the above diagram using pgf/TikZ.

Answer 1

One possibility:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{positioning}

\begin{document}

\begin{tikzpicture}[box/.style={draw,rounded corners,text width=2.5cm,align=center}]
\node[box] (a) {Psychoacustic Model};
\node[left=of a.170,font=\bfseries] (aux1) {Reference};
\node[left=of a.190,font=\bfseries] (aux2) {Degraded};
\node[box,right=of a] (b) {Cognitive Model};
\node[right=of b,font=\bfseries] (c) {Score};
\draw[->] (aux1) -- (a.170);
\draw[->] (aux2) -- (a.190);
\draw[->] (a) -- (b);
\draw[->] (b) -- (c);
\end{tikzpicture}

\end{document}