From 33f10c531765a2bcec83c1bc34ab34774b85c63b Mon Sep 17 00:00:00 2001
From: trondeau <trondeau@221aa14e-8319-0410-a670-987f0aec2ac5>
Date: Tue, 24 Apr 2007 21:34:27 +0000
Subject: using LPF taps for interpolator and decimator now and adding
documentation to wrapper class
git-svn-id: http://gnuradio.org/svn/gnuradio/trunk@5097 221aa14e-8319-0410-a670-987f0aec2ac5
---
gr-cvsd-vocoder/src/python/cvsd.py | 36 ++++++++++++++++++++++++++++++++----
1 file changed, 32 insertions(+), 4 deletions(-)
(limited to 'gr-cvsd-vocoder/src/python/cvsd.py')
diff --git a/gr-cvsd-vocoder/src/python/cvsd.py b/gr-cvsd-vocoder/src/python/cvsd.py
index dcb6bb5074..e1638f3744 100644
--- a/gr-cvsd-vocoder/src/python/cvsd.py
+++ b/gr-cvsd-vocoder/src/python/cvsd.py
@@ -24,12 +24,26 @@ from gnuradio import gr
from gnuradio.vocoder import cvsd_vocoder
class cvsd_encode(gr.hier_block):
- def __init__(self, fg, resample=8):
+ '''
+ This is a wrapper for the CVSD encoder that performs interpolation and filtering
+ necessary to work with the vocoding. It converts an incoming float (+-1) to a short, scales
+ it (to 32000; slightly below the maximum value), interpolates it, and then vocodes it.
+
+ The incoming sampling rate can be anything, though, of course, the higher the sampling rate and the
+ higher the interpolation rate are, the better the sound quality.
+ '''
+
+ def __init__(self, fg, resample=8, bw=0.5):
+ '''
+ When using the CVSD vocoder, appropriate sampling rates are from 8k to 64k with resampling rates
+ from 1 to 8. A rate of 8k with a resampling rate of 8 provides a good quality signal.
+ '''
scale_factor = 32000.0
self.interp = resample
src_scale = gr.multiply_const_ff(scale_factor)
- interp = gr.interp_fir_filter_fff(self.interp, self.interp*(1,))
+ taps = gr.firdes.low_pass(self.interp, self.interp, bw, 2*bw)
+ interp = gr.interp_fir_filter_fff(self.interp, taps)
f2s = gr.float_to_short()
enc = cvsd_vocoder.encode_sb()
@@ -38,13 +52,27 @@ class cvsd_encode(gr.hier_block):
class cvsd_decode(gr.hier_block):
- def __init__(self, fg, resample=8):
+ '''
+ This is a wrapper for the CVSD decoder that performs decimation and filtering
+ necessary to work with the vocoding. It converts an incoming CVSD-encoded short to a float, decodes it
+ to a float, decimates it, and scales it (by 32000; slightly below the maximum value to avoid clipping).
+
+ The sampling rate can be anything, though, of course, the higher the sampling rate and the
+ higher the interpolation rate are, the better the sound quality.
+ '''
+
+ def __init__(self, fg, resample=8, bw=0.5):
+ '''
+ When using the CVSD vocoder, appropriate sampling rates are from 8k to 64k with resampling rates
+ from 1 to 8. A rate of 8k with a resampling rate of 8 provides a good quality signal.
+ '''
scale_factor = 32000.0
self.decim = resample
dec = cvsd_vocoder.decode_bs()
s2f = gr.short_to_float()
- decim = gr.fir_filter_fff(self.decim, (1,))
+ taps = gr.firdes.low_pass(1, 1, bw, 2*bw)
+ decim = gr.fir_filter_fff(self.decim, taps)
sink_scale = gr.multiply_const_ff(1.0/scale_factor)
fg.connect(dec, s2f, decim, sink_scale)
--
cgit v1.2.3