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portapack-mayhem/firmware/baseband/proc_wideband_spectrum.cpp
Jared Boone 291de8f869 Change channel_spectrum type to std::complex<float>. 
Move FFT bit-reversal to complex<int16_t> -> complex<float> copy.
Change window so that adjacent bins have constant(-ish) gain.
Change window to float.
Change time domain samples to accumulate at even intervals over the FFT interval.
2015-10-14 11:10:24 -07:00

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/*
* Copyright (C) 2015 Jared Boone, ShareBrained Technology, Inc.
*
* This file is part of PortaPack.
*
* This program 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 2, or (at your option)
* any later version.
*
* This program 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 this program; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/
#include "proc_wideband_spectrum.hpp"
#include "event_m4.hpp"
#include "i2s.hpp"
using namespace lpc43xx;
#include "dsp_fft.hpp"
#include <cstdint>
#include <cstddef>
#include <array>
/*
Employ window-presum technique with a window constructed to act like a bin filter.
See: http://www.embedded.com/design/real-time-and-performance/4007611/DSP-Tricks-Building-a-practical-spectrum-analyzer
20MHz / 256 bins = 78.125kHz/bin
Taps made with IPython Notebook "specan_lpf", 26041.666667Hz pass, 53400Hz stop, 1024 taps, Remez, gain of 4 * 128.
*/
static constexpr std::array<float, 1024> window_wideband_bin_lpf { {
0.0000000000f, -0.1215729938f, -0.1213842597f, -0.1201684429f,
-0.1201208291f, -0.1190024264f, -0.1190858794f, -0.1180910084f,
-0.1182902140f, -0.1173947314f, -0.1177379144f, -0.1169320615f,
-0.1174165122f, -0.1166760717f, -0.1173065305f, -0.1166353753f,
-0.1174295604f, -0.1168115435f, -0.1177737061f, -0.1171681501f,
-0.1183154633f, -0.1176885372f, -0.1190734477f, -0.1183823726f,
-0.1200564042f, -0.1191925052f, -0.1212624937f, -0.1200347844f,
-0.1227782673f, -0.1205369109f, -0.1247875900f, -0.1173893915f,
-0.1356269751f, -0.1333820215f, -0.1230013683f, -0.1270419996f,
-0.1248521391f, -0.1280766855f, -0.1275474455f, -0.1303677621f,
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-0.1366453783f, -0.1389458751f, -0.1397338876f, -0.1419434716f,
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0.2071598962f, 0.2156750628f, 0.2246834377f, 0.2334738679f,
0.2422305215f, 0.2511740186f, 0.2601619588f, 0.2692982077f,
0.2784363297f, 0.2876515447f, 0.2968698668f, 0.3061706020f,
0.3154820195f, 0.3248945791f, 0.3343234494f, 0.3438662338f,
0.3534259170f, 0.3630855246f, 0.3727544495f, 0.3825072994f,
0.3922658126f, 0.4021151299f, 0.4119710813f, 0.4219304098f,
0.4318755419f, 0.4419066050f, 0.4519266790f, 0.4620411273f,
0.4721924196f, 0.4824099358f, 0.4925918161f, 0.5029672026f,
0.5131676220f, 0.5237112702f, 0.5340474666f, 0.5443687487f,
0.5549596923f, 0.5655037792f, 0.5760846623f, 0.5866412762f,
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0.6399890869f, 0.6507775481f, 0.6615869909f, 0.6724215836f,
0.6832601692f, 0.6941326055f, 0.7050115342f, 0.7159351783f,
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0.7708626189f, 0.7819213638f, 0.7929898181f, 0.8041032024f,
0.8151863856f, 0.8262675846f, 0.8374347030f, 0.8485124885f,
0.8596901081f, 0.8708298046f, 0.8818521053f, 0.8932043400f,
0.9043106868f, 0.9154712945f, 0.9265928796f, 0.9377943260f,
0.9489884395f, 0.9602246825f, 0.9714051258f, 0.9826151929f,
0.9937649659f, 1.0049460392f, 1.0160814715f, 1.0272496293f,
1.0383880993f, 1.0495571434f, 1.0606883842f, 1.0718420204f,
1.0829385916f, 1.0940532343f, 1.1051116703f, 1.1161955290f,
1.1272425119f, 1.1382946085f, 1.1492896227f, 1.1602787038f,
1.1712107201f, 1.1822261399f, 1.1931082102f, 1.2040321660f,
1.2149338949f, 1.2257216453f, 1.2366886195f, 1.2474232220f,
1.2581260885f, 1.2689166363f, 1.2796266048f, 1.2903413723f,
1.3009452557f, 1.3115347597f, 1.3220588330f, 1.3325885128f,
1.3430577723f, 1.3535351287f, 1.3639358829f, 1.3743362159f,
1.3846448962f, 1.3949381321f, 1.4051428918f, 1.4153304829f,
1.4254416597f, 1.4355455123f, 1.4455694200f, 1.4555829383f,
1.4654880955f, 1.4753745521f, 1.4851755647f, 1.4949664411f,
1.5047009642f, 1.5143471956f, 1.5238981621f, 1.5335015901f,
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1.5801889794f, 1.5893352932f, 1.5983995178f, 1.6073964215f,
1.6163275268f, 1.6252361387f, 1.6340558312f, 1.6428196478f,
1.6514803963f, 1.6600728279f, 1.6685645243f, 1.6769969948f,
1.6853322111f, 1.6936257655f, 1.7018206388f, 1.7099724793f,
1.7180180271f, 1.7260006052f, 1.7338708023f, 1.7416709937f,
1.7493721167f, 1.7570307435f, 1.7645736334f, 1.7720587141f,
1.7793864240f, 1.7866595518f, 1.7939083209f, 1.8009680396f,
1.8080175914f, 1.8149423807f, 1.8217244084f, 1.8285934275f,
1.8351580541f, 1.8417084040f, 1.8481458306f, 1.8545405038f,
1.8608040839f, 1.8669819454f, 1.8730100097f, 1.8789794347f,
1.8848148272f, 1.8906028239f, 1.8962629246f, 1.9018629597f,
1.9073312666f, 1.9127216689f, 1.9179684698f, 1.9231368617f,
1.9281575220f, 1.9331147367f, 1.9379346294f, 1.9426980945f,
1.9473253537f, 1.9518608547f, 1.9562473102f, 1.9605563249f,
1.9647377083f, 1.9689130417f, 1.9728201948f, 1.9767204935f,
1.9804869777f, 1.9840965410f, 1.9877044695f, 1.9910612418f,
1.9943519434f, 1.9976117863f, 2.0006898142f, 2.0036817820f,
2.0065068911f, 2.0092612533f, 2.0118899336f, 2.0144381201f,
2.0168403950f, 2.0191500613f, 2.0212978024f, 2.0233571150f,
2.0252586877f, 2.0270797012f, 2.0287613011f, 2.0303632435f,
2.0318318976f, 2.0332139460f, 2.0344458593f, 2.0355811762f,
2.0365507956f, 2.0374411193f, 2.0382032761f, 2.0388791314f,
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} };
void WidebandSpectrum::execute(buffer_c8_t buffer) {
// 2048 complex8_t samples per buffer.
// 102.4us per buffer. 20480 instruction cycles per buffer.
static int phase = 0;
if( phase == 0 ) {
std::fill(spectrum.begin(), spectrum.end(), 0);
}
if( (phase & 7) == 0 ) {
const size_t window_offset = (phase >> 3) * 256;
const auto window_p = &window_wideband_bin_lpf[window_offset];
for(size_t i=0; i<channel_spectrum.size(); i++) {
spectrum[i] += std::complex<float> { buffer.p[i].real() * window_p[i], buffer.p[i].imag() * window_p[i] };
}
}
if( phase == 23 ) {
if( channel_spectrum_request_update == false ) {
fft_swap(spectrum, channel_spectrum);
channel_spectrum_sampling_rate = buffer.sampling_rate;
channel_filter_pass_frequency = 0;
channel_filter_stop_frequency = 0;
channel_spectrum_request_update = true;
events_flag(EVT_MASK_SPECTRUM);
phase = 0;
}
} else {
phase++;
}
i2s::i2s0::tx_mute();
}
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