From 515e40039e614ac86fb4c7be8dc4d067aa2bd9a3 Mon Sep 17 00:00:00 2001
From: Andy Walls <awalls@md.metrocast.net>
Date: Wed, 30 Mar 2016 09:15:45 -0400
Subject: gr-analog: Add safety and default for FM preemphasis filter
The FM preemphasis filter design now precludes the user from
inducing a pole on the unit circle at z = -1.0 and z = 1.0.
A pole at either of these locations makes the filter unstable and
useless: feeding back "+/-inf" into an IIR filter has no good
recovery.
Also provide a reasonable, maximally safe default of 0.925*fs/2.0
for the high frequency corner, fh. This keeps the slope of the
preemphasis filter looking reasonable sane in the whole band; at
least for tau=75e-6 and fs=48000.
---
gr-analog/examples/fmtest.py | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
(limited to 'gr-analog/examples/fmtest.py')
diff --git a/gr-analog/examples/fmtest.py b/gr-analog/examples/fmtest.py
index 22448e6428..7ed08cafbe 100755
--- a/gr-analog/examples/fmtest.py
+++ b/gr-analog/examples/fmtest.py
@@ -48,8 +48,8 @@ class fmtx(gr.hier_block2):
gr.io_signature(1, 1, gr.sizeof_float),
gr.io_signature(1, 1, gr.sizeof_gr_complex))
- fmtx = analog.nbfm_tx(audio_rate, if_rate, max_dev=5e3, tau=75e-6,
- fh=0.0)
+ fmtx = analog.nbfm_tx(audio_rate, if_rate, max_dev=5e3,
+ tau=75e-6, fh=0.925*if_rate/2.0)
# Local oscillator
lo = analog.sig_source_c(if_rate, # sample rate
--
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