forked from gqrx-sdr/gqrx
-
Notifications
You must be signed in to change notification settings - Fork 0
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
Apply de-emphasis after stereo demodulation
- Loading branch information
Showing
10 changed files
with
203 additions
and
108 deletions.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,104 @@ | ||
| /* -*- c++ -*- */ | ||
| /* | ||
| * Gqrx SDR: Software defined radio receiver powered by GNU Radio and Qt | ||
| * http://gqrx.dk/ | ||
| * | ||
| * Copyright 2020 Clayton Smith VE3IRR. | ||
| * | ||
| * Gqrx is free software; you can redistribute it and/or modify | ||
| * it under the terms of the GNU General Public License as published by | ||
| * the Free Software Foundation; either version 3, or (at your option) | ||
| * any later version. | ||
| * | ||
| * Gqrx is distributed in the hope that it will be useful, | ||
| * but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
| * GNU General Public License for more details. | ||
| * | ||
| * You should have received a copy of the GNU General Public License | ||
| * along with Gqrx; see the file COPYING. If not, write to | ||
| * the Free Software Foundation, Inc., 51 Franklin Street, | ||
| * Boston, MA 02110-1301, USA. | ||
| */ | ||
| #include <gnuradio/filter/firdes.h> | ||
| #include <gnuradio/io_signature.h> | ||
| #include <iostream> | ||
| #include <math.h> | ||
| #include "dsp/fm_deemph.h" | ||
|
|
||
|
|
||
| /* Create a new instance of fm_deemph and return a boost shared_ptr. */ | ||
| fm_deemph_sptr make_fm_deemph(float quad_rate, double tau) | ||
| { | ||
| return gnuradio::get_initial_sptr(new fm_deemph(quad_rate, tau)); | ||
| } | ||
|
|
||
| static const int MIN_IN = 1; /* Mininum number of input streams. */ | ||
| static const int MAX_IN = 1; /* Maximum number of input streams. */ | ||
| static const int MIN_OUT = 1; /* Minimum number of output streams. */ | ||
| static const int MAX_OUT = 1; /* Maximum number of output streams. */ | ||
|
|
||
| fm_deemph::fm_deemph(float quad_rate, double tau) | ||
| : gr::hier_block2 ("fm_deemph", | ||
| gr::io_signature::make (MIN_IN, MAX_IN, sizeof (float)), | ||
| gr::io_signature::make (MIN_OUT, MAX_OUT, sizeof (float))), | ||
| d_quad_rate(quad_rate) | ||
| { | ||
| /* de-emphasis */ | ||
| d_fftaps.resize(2); | ||
| d_fbtaps.resize(2); | ||
| calculate_iir_taps(tau); | ||
| d_deemph = gr::filter::iir_filter_ffd::make(d_fftaps, d_fbtaps, false); | ||
|
|
||
| connect(self(), 0, d_deemph, 0); | ||
| connect(d_deemph, 0, self(), 0); | ||
| } | ||
|
|
||
| fm_deemph::~fm_deemph () | ||
| { | ||
| } | ||
|
|
||
| /*! \brief Set FM de-emphasis time constant. | ||
| * \param tau The new time costant. | ||
| */ | ||
| void fm_deemph::set_tau(double tau) | ||
| { | ||
| calculate_iir_taps(tau); | ||
| d_deemph->set_taps(d_fftaps, d_fbtaps); | ||
| } | ||
|
|
||
| /*! \brief Calculate taps for FM de-emph IIR filter. */ | ||
| void fm_deemph::calculate_iir_taps(double tau) | ||
| { | ||
| if (tau > 1.0e-9) | ||
| { | ||
| // copied from fm_emph.py in gr-analog | ||
| double w_c; // Digital corner frequency | ||
| double w_ca; // Prewarped analog corner frequency | ||
| double k, z1, p1, b0; | ||
| double fs = d_quad_rate; | ||
|
|
||
| w_c = 1.0 / tau; | ||
| w_ca = 2.0 * fs * 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); | ||
|
|
||
| d_fftaps[0] = b0; | ||
| d_fftaps[1] = -z1 * b0; | ||
| d_fbtaps[0] = 1.0; | ||
| d_fbtaps[1] = -p1; | ||
| } | ||
| else | ||
| { | ||
| d_fftaps[0] = 1.0; | ||
| d_fftaps[1] = 0.0; | ||
| d_fbtaps[0] = 0.0; | ||
| d_fbtaps[1] = 0.0; | ||
| } | ||
| } |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,71 @@ | ||
| /* -*- c++ -*- */ | ||
| /* | ||
| * Gqrx SDR: Software defined radio receiver powered by GNU Radio and Qt | ||
| * http://gqrx.dk/ | ||
| * | ||
| * Copyright 2020 Clayton Smith VE3IRR. | ||
| * | ||
| * Gqrx is free software; you can redistribute it and/or modify | ||
| * it under the terms of the GNU General Public License as published by | ||
| * the Free Software Foundation; either version 3, or (at your option) | ||
| * any later version. | ||
| * | ||
| * Gqrx is distributed in the hope that it will be useful, | ||
| * but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
| * GNU General Public License for more details. | ||
| * | ||
| * You should have received a copy of the GNU General Public License | ||
| * along with Gqrx; see the file COPYING. If not, write to | ||
| * the Free Software Foundation, Inc., 51 Franklin Street, | ||
| * Boston, MA 02110-1301, USA. | ||
| */ | ||
| #pragma once | ||
|
|
||
| #include <gnuradio/filter/iir_filter_ffd.h> | ||
| #include <gnuradio/hier_block2.h> | ||
| #include <vector> | ||
|
|
||
| class fm_deemph; | ||
| typedef boost::shared_ptr<fm_deemph> fm_deemph_sptr; | ||
|
|
||
| /*! \brief Return a shared_ptr to a new instance of fm_deemph. | ||
| * \param quad_rate The input sample rate. | ||
| * \param tau De-emphasis time constant in seconds (75us in US, 50us in EUR, 0.0 disables). | ||
| * | ||
| * This is effectively the public constructor. To avoid accidental use | ||
| * of raw pointers, fm_deemph's constructor is private. | ||
| * make_rx_dmod_fm is the public interface for creating new instances. | ||
| */ | ||
| fm_deemph_sptr make_fm_deemph(float quad_rate, double tau=50.0e-6); | ||
|
|
||
| /*! \brief FM demodulator. | ||
| * \ingroup DSP | ||
| * | ||
| * This class implements the FM demodulator using the gr_quadrature_demod block. | ||
| * It also provides de-emphasis with variable time constant (use 0.0 to disable). | ||
| * | ||
| */ | ||
| class fm_deemph : public gr::hier_block2 | ||
| { | ||
|
|
||
| public: | ||
| fm_deemph(float quad_rate, double tau); // FIXME: should be private | ||
| ~fm_deemph(); | ||
|
|
||
| void set_tau(double tau); | ||
|
|
||
| private: | ||
| /* GR blocks */ | ||
| gr::filter::iir_filter_ffd::sptr d_deemph; /*! De-emphasis IIR filter. */ | ||
|
|
||
| /* other parameters */ | ||
| float d_quad_rate; /*! Quadrature rate. */ | ||
|
|
||
| /* De-emph IIR filter taps */ | ||
| std::vector<double> d_fftaps; /*! Feed forward taps. */ | ||
| std::vector<double> d_fbtaps; /*! Feed back taps. */ | ||
|
|
||
| void calculate_iir_taps(double tau); | ||
|
|
||
| }; |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Oops, something went wrong.