1 files changed, 41 insertions, 0 deletions
diff --git a/fir_window_hamming.awk b/fir_window_hamming.awk
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+#!/usr/bin/awk -f
+
+### fir_window_hamming.awk
+# generate a Hamming window
+# R.W. Hamming, 'Digital Filters': H = '0.23 0.54 0.23'
+# https://en.wikipedia.org/wiki/Window_function provides a few values for the
+# 'a0' and 'a1' parameters of the raised cosine.
+
+
+# Hamming window (raised cosine)
+function hamming(n) {
+    # optimal values for equal-ripple
+    #a0 = 0.53836
+    #a1 = 0.46164
+
+    a0 = (25.0/46.0)
+    a1 = (21.0/46.0)
+    return a0 + a1*cos((pi*n)/M)
+}
+
+
+BEGIN {
+
+    ARGV[1] ? N = ARGV[1] : N = 0
+    ARGV[2] ? OFMT = "%." ARGV[2] "g" : OFMT = "%g"
+
+    # window interval goes from -M to M
+    M = 0.5*(N - 1)
+    pi = 4*atan2(1,1)
+
+    for (n=-M; n<=M; n++) {
+        if (N > 1 && M > 0) {
+            w[n] = hamming(n)
+            print n + M, w[n]/M
+        }
+        else {
+            print n + M, 1.0
+        }
+    }
+}
+