Restore the branch

Tools/DeEmphasis.py

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+#based on https://github.com/gnuradio/gnuradio/blob/master/gr-analog/python/analog/fm_emph.py
+
+import math
+import cmath
+import numpy as np
+import scipy.signal as signal
+import pylab as pl
+
+tau = 750e-6
+fs = 8000
+fh = 2700
+
+# Digital corner frequency
+w_c = 1.0 / tau
+
+# Prewarped analog corner frequency
+w_ca = 2.0 * fs * math.tan(w_c / (2.0 * fs))
+
+# Resulting digital pole, zero, and gain term from the bilinear
+# transformation of H(s) = w_ca / (s + w_ca) to
+# H(z) = b0 (1 - z1 z^-1)/(1 - p1 z^-1)
+k = -w_ca / (2.0 * fs)
+z1 = -1.0
+p1 = (1.0 + k) / (1.0 - k)
+b0 = -k / (1.0 - k)
+
+btaps = [ b0 * 1.0, b0 * -z1, 0 ]
+ataps = [      1.0,      -p1, 0 ]
+
+# Since H(s = 0) = 1.0, then H(z = 1) = 1.0 and has 0 dB gain at DC
+
+
+taps = np.concatenate((btaps, ataps), axis=0)
+print("Taps")
+print(*taps, "", sep=",", end="\n")
+
+f,h = signal.freqz(btaps,ataps, fs=fs)
+pl.plot(f, 20*np.log10(np.abs(h)))
+pl.xlabel('frequency/Hz')
+pl.ylabel('gain/dB')
+pl.ylim(top=0,bottom=-30)
+pl.xlim(left=0, right=fh*2.5)
+pl.show()