\section{Filters}

\begin{figure}
  \centering
  \begin{tikzpicture}[
      axis tick/.style = {
        inner sep = 1mm,
        outer sep = 1mm,
      },
      x axis tick/.style = {
        axis tick,
        path picture = {
          \draw[thick, -]
            ($(path picture bounding box) + (0,.1)$) --
            ($(path picture bounding box) - (0,.1)$);
        }
      },
      y axis tick/.style = {
        axis tick,
        path picture = {
          \draw[thick, -]
            ($(path picture bounding box) + (.1,0)$) --
            ($(path picture bounding box) - (.1,0)$);
        }
      }
    ]

    \pgfmathsetmacro\xlen{5}
    \pgfmathsetmacro\ylen{3}

    \coordinate (O) at (0,0);
    \draw[thick, ->] (O) to
      % node[pos = .5, x axis tick, label = -90:1] {}
      node[pos = .4, x axis tick, label = -90:\(\Omega_D\)] (OmegaD) {}
      node[pos = .65, x axis tick, label = -90:\(\Omega_S\)] (OmegaS) {}
      ++(\xlen,0) node[right] {\(\Omega\)};

    \draw[thick, ->] (O) to
      node[pos = .2, y axis tick, label = 180:\(A_\text{max}\)] (Amax) {}
      node[pos = .7, y axis tick, label = 180:\(A_\text{min}\)] (Amin) {}
      ++(0,\ylen) node[above] {\(A\)};

    \draw[dashed, lightgray]
      (Amin) -- ++(\xlen,0)
      (Amax) -- ++(\xlen,0)
      (OmegaD) -- ++(0,\ylen)
      (OmegaS) -- ++(0,\ylen);

    \draw[very thick, red!80!black] (Amax) -| ($(OmegaD) +(0,3)$);
    \draw[very thick, red!80!black] (OmegaS) -- (Amin -| OmegaS) -- ++(1.5,0);

    \node[align = center] at (1,1.3) {Stamp \\ (passband)};
    \node[align = center] at (4.3,1.3) {Mold \\ (stopband)};

  \end{tikzpicture}
\end{figure}

% vim:ts=2 sw=2 et:
