3 files changed, 62 insertions, 0 deletions
diff --git a/SigSys.tex b/SigSys.tex
index e2d1952..192a703 100644
--- a/SigSys.tex
+++ b/SigSys.tex
@@ -67,10 +67,15 @@
 \setcounter{page}{1}
 \pagenumbering{arabic}
 
+\part{Signals and Systems}
 \input{tex/signals}
 \input{tex/lti}
 \input{tex/lti-freq}
 \input{tex/state-space}
 \input{tex/filters}
 
+\part{Mathematics}
+% linear algebra
+% fourier and laplace transforms
+
 \end{document}
diff --git a/build/SigSys.pdf b/build/SigSys.pdf
index 1422224..09acfee 100644
--- a/build/SigSys.pdf
+++ b/build/SigSys.pdf
diff --git a/tex/filters.tex b/tex/filters.tex
index 4271e35..e785e0a 100644
--- a/tex/filters.tex
+++ b/tex/filters.tex
@@ -1 +1,58 @@
 \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: