tinymodem::FSKDemodulator Class Reference

FSK bit and frame analysis (port of minimodem's fsk.c). Instead of a full FFT we use the Goertzel algorithm from the AudioTools to determine the magnitude of the mark and space bands. The bands are defined like the FFT bins of minimodem, so the results are equivalent. More...

#include <FSKDemodulator.h>

Public Member Functions
bool	begin (float sample_rate, float f_mark, float f_space, float filter_bw)
	Defines the tones and the filter bandwidth: returns false if invalid.
float	findFrame (const float *samples, unsigned frame_nsamples, unsigned try_first_sample, unsigned try_max_nsamples, unsigned try_step_nsamples, float try_confidence_search_limit, const char *expect_bits_string, uint64_t *bits_outp, float *ampl_outp, unsigned *frame_start_outp)
int	detectCarrier (const float *samples, unsigned nsamples, float min_mag_threshold)
void	setTonesByBandShift (unsigned b_mark, int b_shift)
	Redefines the mark and space band.
unsigned	fftSize ()
unsigned	bandCount ()
float	bandWidth ()
unsigned	markBand ()
unsigned	spaceBand ()

Protected Member Functions
float	bandFrequency (unsigned band)
	center frequency of the FFT bin which corresponds to the band
bool	setupDetector (audio_tools::GoertzelDetector &detector, unsigned band, unsigned nsamples)
float	magnitude (audio_tools::GoertzelDetector &detector, const float *samples, unsigned nsamples)
	unscaled magnitude of the band over n samples
float	bandMagnitude (const float *samples, unsigned nsamples, unsigned band)
void	bitAnalyze (const float *samples, unsigned bit_nsamples, unsigned *bit_outp, float *bit_signal_mag_outp, float *bit_noise_mag_outp)
float	frameAnalyze (const float *samples, float samples_per_bit, int n_bits, const char *expect_bits, uint64_t *bits_outp, float *ampl_outp)
	returns confidence value [0.0 to INFINITY]

Protected Attributes
float	sample_rate = 0.0f
float	f_mark = 0.0f
float	f_space = 0.0f
float	band_width = 0.0f
unsigned	fftsize = 0
unsigned	nbands = 0
unsigned	b_mark = 0
unsigned	b_space = 0
audio_tools::GoertzelDetector	mark_detector
audio_tools::GoertzelDetector	space_detector
unsigned	detector_nsamples = 0

Static Protected Attributes
static constexpr int	MAX_BITS = 72

Detailed Description

FSK bit and frame analysis (port of minimodem's fsk.c). Instead of a full FFT we use the Goertzel algorithm from the AudioTools to determine the magnitude of the mark and space bands. The bands are defined like the FFT bins of minimodem, so the results are equivalent.

Copyright

GPLv3

Member Function Documentation

bandCount()

unsigned tinymodem::FSKDemodulator::bandCount ( )

inline

bandFrequency()

float tinymodem::FSKDemodulator::bandFrequency ( unsigned band )

inlineprotected

center frequency of the FFT bin which corresponds to the band

bandMagnitude()

float tinymodem::FSKDemodulator::bandMagnitude ( const float * samples, unsigned nsamples, unsigned band )

inlineprotected

bandWidth()

float tinymodem::FSKDemodulator::bandWidth ( )

inline

begin()

bool tinymodem::FSKDemodulator::begin ( float sample_rate, float f_mark, float f_space, float filter_bw )

inline

Defines the tones and the filter bandwidth: returns false if invalid.

bitAnalyze()

void tinymodem::FSKDemodulator::bitAnalyze ( const float * samples, unsigned bit_nsamples, unsigned * bit_outp, float * bit_signal_mag_outp, float * bit_noise_mag_outp )

inlineprotected

detectCarrier()

int tinymodem::FSKDemodulator::detectCarrier ( const float * samples, unsigned nsamples, float min_mag_threshold )

inline

Returns the band with the max magnitude or -1. Port of fsk_detect_carrier()

fftSize()

unsigned tinymodem::FSKDemodulator::fftSize ( )

inline

findFrame()

float tinymodem::FSKDemodulator::findFrame ( const float * samples, unsigned frame_nsamples, unsigned try_first_sample, unsigned try_max_nsamples, unsigned try_step_nsamples, float try_confidence_search_limit, const char * expect_bits_string, uint64_t * bits_outp, float * ampl_outp, unsigned * frame_start_outp )

inline

Analyzes the expected bits starting at samples and returns the confidence: [0.0 to INFINITY]. Port of fsk_find_frame().

frameAnalyze()

float tinymodem::FSKDemodulator::frameAnalyze ( const float * samples, float samples_per_bit, int n_bits, const char * expect_bits, uint64_t * bits_outp, float * ampl_outp )

inlineprotected

returns confidence value [0.0 to INFINITY]

magnitude()

float tinymodem::FSKDemodulator::magnitude ( audio_tools::GoertzelDetector & detector, const float * samples, unsigned nsamples )

inlineprotected

unscaled magnitude of the band over n samples

markBand()

unsigned tinymodem::FSKDemodulator::markBand ( )

inline

setTonesByBandShift()

void tinymodem::FSKDemodulator::setTonesByBandShift ( unsigned b_mark, int b_shift )

inline

Redefines the mark and space band.

setupDetector()

bool tinymodem::FSKDemodulator::setupDetector ( audio_tools::GoertzelDetector & detector, unsigned band, unsigned nsamples )

inlineprotected

spaceBand()

unsigned tinymodem::FSKDemodulator::spaceBand ( )

inline

Member Data Documentation

b_mark

unsigned tinymodem::FSKDemodulator::b_mark = 0

protected

b_space

unsigned tinymodem::FSKDemodulator::b_space = 0

protected

band_width

float tinymodem::FSKDemodulator::band_width = 0.0f

protected

detector_nsamples

unsigned tinymodem::FSKDemodulator::detector_nsamples = 0

protected

f_mark

float tinymodem::FSKDemodulator::f_mark = 0.0f

protected

f_space

float tinymodem::FSKDemodulator::f_space = 0.0f

protected

fftsize

unsigned tinymodem::FSKDemodulator::fftsize = 0

protected

mark_detector

audio_tools::GoertzelDetector tinymodem::FSKDemodulator::mark_detector

protected

MAX_BITS

int tinymodem::FSKDemodulator::MAX_BITS = 72

staticconstexprprotected

nbands

unsigned tinymodem::FSKDemodulator::nbands = 0

protected

sample_rate

float tinymodem::FSKDemodulator::sample_rate = 0.0f

protected

space_detector

audio_tools::GoertzelDetector tinymodem::FSKDemodulator::space_detector

protected

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The documentation for this class was generated from the following file:

• src/modem/FSKDemodulator.h