From 5c2659deaa21cdb22797ca553cab53ea14910d0b Mon Sep 17 00:00:00 2001 From: Geoffrey Merck Date: Fri, 24 Apr 2020 09:10:50 +0200 Subject: [PATCH] Add FM filtering --- FM.cpp | 14 ++-- FM.h | 6 +- FMDirectForm1.h | 114 ++++++++++++++++++++++++++++++++ FMGenerateFilterCoefficients.py | 45 +++++++++++++ 4 files changed, 170 insertions(+), 9 deletions(-) create mode 100644 FMDirectForm1.h create mode 100644 FMGenerateFilterCoefficients.py diff --git a/FM.cpp b/FM.cpp index 1ec448b..03aa6ec 100644 --- a/FM.cpp +++ b/FM.cpp @@ -23,9 +23,9 @@ // 3 stage IIR Butterworth filter generated (if you change the order change the size of m_filterState). Also change the ordre in init call below // 0.2db band pass ripple // 300 - 2700Hz -q15_t FILTER_COEFFS[] = { 362, 724, 362,16384,-18947,10676, 14,//1st stage - 16384, 0, -16384,16384,-25170, 9526, 14,//2nd stage - 16384,-32768, 16384,16384,-32037,15730,14};//3rd stage +q15_t FILTER_COEFFS[] = {362,724,362,16384,-18947,10676, + 16384,0,-16384,16384,-25170,9526, + 16384,-32768,16384,16384,-32037,15730}; CFM::CFM() : @@ -44,14 +44,14 @@ m_kerchunkTimer(), m_ackMinTimer(), m_ackDelayTimer(), m_hangTimer(), -m_filter() +m_filterStage1( 724, 1448, 724, 32768, -37895, 21352), +m_filterStage2(32768, 0,-32768, 32768, -50339, 19052), +m_filterStage3(32768, -65536, 32768, 32768, -64075, 31460) { - arm_biquad_cascade_df1_init_q15(&m_filter, 3, FILTER_COEFFS, m_filterState, 0); } void CFM::samples(q15_t* samples, uint8_t length) { - arm_biquad_casd_df1_inst_q15* filterPtr = &m_filter; uint8_t i = 0; for (; i < length; i++) { q15_t currentSample = samples[i];//save to a local variable to avoid indirection on every access @@ -97,7 +97,7 @@ void CFM::samples(q15_t* samples, uint8_t length) if (!m_callsign.isRunning() && !m_rfAck.isRunning()) currentSample += m_timeoutTone.getAudio(); - arm_biquad_cascade_df1_fast_q15(filterPtr, samples +i, ¤tSample, 1); + currentSample = q15_t(m_filterStage3.filter(m_filterStage2.filter(m_filterStage1.filter(currentSample)))); currentSample += m_ctcssTX.getAudio(); diff --git a/FM.h b/FM.h index 474f36d..77a3d81 100644 --- a/FM.h +++ b/FM.h @@ -26,6 +26,7 @@ #include "FMTimeout.h" #include "FMKeyer.h" #include "FMTimer.h" +#include "FMDirectForm1.h" enum FM_STATE { FS_LISTENING, @@ -70,8 +71,9 @@ private: CFMTimer m_ackMinTimer; CFMTimer m_ackDelayTimer; CFMTimer m_hangTimer; - arm_biquad_casd_df1_inst_q15 m_filter; - q15_t m_filterState[12];//must be filterOrder * 4 long + CFMDirectFormI m_filterStage1; + CFMDirectFormI m_filterStage2; + CFMDirectFormI m_filterStage3; void stateMachine(bool validSignal, uint8_t length); void listeningState(bool validSignal); diff --git a/FMDirectForm1.h b/FMDirectForm1.h new file mode 100644 index 0000000..857e0a6 --- /dev/null +++ b/FMDirectForm1.h @@ -0,0 +1,114 @@ + +/******************************************************************************* +This header file has been taken from: +"A Collection of Useful C++ Classes for Digital Signal Processing" +By Vinnie Falco +Bernd Porr adapted it for Linux and turned it into a filter using +fixed point arithmetic. +-------------------------------------------------------------------------------- +License: MIT License (http://www.opensource.org/licenses/mit-license.php) +Copyright (c) 2009 by Vinnie Falco +Copyright (C) 2013-2017, Bernd Porr, mail@berndporr.me.uk +Copyright (C) 2020 , Mario Molitor , mario_molitor@web.de +Permission is hereby granted, free of charge, to any person obtaining a copy +of this software and associated documentation files (the "Software"), to deal +in the Software without restriction, including without limitation the rights +to use, copy, modify, merge, publish, distribute, sublicense, and/or sell +copies of the Software, and to permit persons to whom the Software is +furnished to do so, subject to the following conditions: +The above copyright notice and this permission notice shall be included in +all copies or substantial portions of the Software. +THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR +IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, +FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE +AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER +LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, +OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN +THE SOFTWARE. +*******************************************************************************/ + +// based on https://raw.githubusercontent.com/berndporr/iir_fixed_point/master/DirectFormI.h + +#include "Globals.h" + +#ifndef DIRECTFORMI_HPP_ +#define DIRECTFORMI_HPP_ +class CFMDirectFormI +{ +public: + + // convenience function which takes the a0 argument but ignores it! + CFMDirectFormI(const q31_t b0, const q31_t b1, const q31_t b2, + const q31_t, const q31_t a1, const q31_t a2) + { + // FIR coefficients + c_b0 = b0; + c_b1 = b1; + c_b2 = b2; + // IIR coefficients + c_a1 = a1; + c_a2 = a2; + reset(); + } + + CFMDirectFormI(const CFMDirectFormI &my) + { + // delay line + m_x2 = my.m_x2; // x[n-2] + m_y2 = my.m_y2; // y[n-2] + m_x1 = my.m_x1; // x[n-1] + m_y1 = my.m_y1; // y[n-1] + + // coefficients + c_b0 = my.c_b0; + c_b1 = my.c_b1; + c_b2 = my.c_b2; // FIR + c_a1 = my.c_a1; + c_a2 = my.c_a2; // IIR + + // scaling factor + q_scaling = my.q_scaling; // 2^q_scaling + } + + void reset () + { + m_x1 = 0; + m_x2 = 0; + m_y1 = 0; + m_y2 = 0; + } + + // filtering operation: one sample in and one out + inline q15_t filter(const q15_t in) + { + // calculate the output + register q31_t out_upscaled = c_b0 * in //F4FXL puting stauration here made everything quiet, not sure why + + c_b1 * m_x1 + + c_b2 * m_x2 + - c_a1 * m_y1 + - c_a2 * m_y2; + + q15_t out = __SSAT(out_upscaled >> 15, 15); + + // update the delay lines + m_x2 = m_x1; + m_y2 = m_y1; + m_x1 = in; + m_y1 = out; + + return out; + } + +private: + // delay line + q31_t m_x2; // x[n-2] + q31_t m_y2; // y[n-2] + q31_t m_x1; // x[n-1] + q31_t m_y1; // y[n-1] + + // coefficients + q31_t c_b0,c_b1,c_b2; // FIR + q31_t c_a1,c_a2; // IIR +}; + +#endif /* DIRECTFORMI_HPP_ */ \ No newline at end of file diff --git a/FMGenerateFilterCoefficients.py b/FMGenerateFilterCoefficients.py new file mode 100644 index 0000000..84ea62b --- /dev/null +++ b/FMGenerateFilterCoefficients.py @@ -0,0 +1,45 @@ +# based on https://github.com/berndporr/iir_fixed_point/blob/master/gen_coeff.py + +import numpy as np +import scipy.signal as signal +import pylab as pl + +# Calculate the coefficients for a pure fixed point +# integer filter + +# sampling rate +fs = 24000 + +# cutoffs +f1 = 300 +f2 = 2700 +# ripple +rp = 0.2 + +# scaling factor in bits, do not change ! +q = 15 +# scaling factor as facor... +scaling_factor = 2**q + +# let's generate a sequence of 2nd order IIR filters +#sos = signal.butter(2,[f1/fs*2,f2/fs*2],'pass',output='sos') +sos = signal.cheby1(3,rp,[f1/fs*2,f2/fs*2],'bandpass', output='sos') + +sos = np.round((sos) * scaling_factor) + +# print coefficients +for biquad in sos: + for coeff in biquad: + print(int(coeff),",",sep="",end="") + #print((coeff),",",sep="",end="") + print("") + +# plot the frequency response +b,a = signal.sos2tf(sos) +w,h = signal.freqz(b,a) +pl.plot(w/np.pi/2*fs,20*np.log(np.abs(h))) +pl.xlabel('frequency/Hz'); +pl.ylabel('gain/dB'); +pl.ylim(top=1,bottom=-20); +pl.xlim(left=250, right=12000); +pl.show() \ No newline at end of file