%!TEX program = xelatex
\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{calc} 
\usetikzlibrary{arrows,positioning}
\usepackage{fontspec}
\setmainfont{Charis SIL}
\begin{document}
\tikzstyle{m1} = [rectangle, rounded corners, minimum width=3cm, minimum height=1cm,text centered, draw=black, fill=blue!10]
\tikzstyle{m4} = [rectangle, rounded corners, minimum width=3cm, minimum height=1cm,text centered, draw=black, fill=purple!10]
\tikzstyle{m2} = [rectangle, rounded corners, minimum width=3cm, minimum height=1cm,text centered, draw=black, fill=red!10]
\tikzstyle{m3} = [rectangle, rounded corners, minimum width=3cm, minimum height=1cm,text centered, draw=black, fill=red!10]
\tikzstyle{spoken} = [rectangle, rounded corners, minimum width=3cm, minimum height=1cm,text centered, draw=black, fill=green!10]
\tikzstyle{textst} = [rectangle, rounded corners, minimum width=3cm, minimum height=1cm,text centered, draw=black, fill=gray!10,font=\ttfamily]
\tikzstyle{arrow} = [thick,->,>=stealth]
\begin{tikzpicture}[node distance=0.5cm]
  \node (concept) [spoken] {Spoken Query};
   \node (adc) [m1,below= of concept] {\textbf{Signal Processing (ADC, VAD, Denoise)}};
   \node (m2) [m1,below= of adc] {\textbf{Acoustical Feature Extraction}};
   \node (amodel) [m1,below= of m2] {\textbf{Joint Text/Acoustics Model}};
\node (output) [textst,below= of amodel] {\textbf{Output Text}};
\draw [arrow] (concept) -- (adc);
\draw [arrow] (adc) -- (m2);
\draw [arrow] (m2) -- (amodel);
\draw [arrow] (amodel) -- (output);

\end{tikzpicture}

\end{document}
