Pulse Shaper

Collaboration diagram for Pulse Shaper:

Topics
	Pulse Shaper States

Data Structures
struct	sstvenc_pulseshape

Macros
#define	SSTVENC_PS_HOLD_TIME_INF   SSTVENC_TS_INFINITE

Functions
void	sstvenc_ps_reset_samples (struct sstvenc_pulseshape *const ps, uint32_t hold_time)
void	sstvenc_ps_reset (struct sstvenc_pulseshape *const ps, double hold_time, uint8_t time_unit)
void	sstvenc_ps_init (struct sstvenc_pulseshape *const ps, double amplitude, double rise_time, double hold_time, double fall_time, uint32_t sample_rate, uint8_t time_unit)
void	sstvenc_ps_advance (struct sstvenc_pulseshape *const ps)
void	sstvenc_ps_compute (struct sstvenc_pulseshape *const ps)
size_t	sstvenc_psosc_fill_buffer (struct sstvenc_pulseshape *const ps, struct sstvenc_oscillator *const osc, double *buffer, size_t buffer_sz)

Detailed Description

The purpose of this module is to drive the amplitude of an oscillator to ensure the waveform generated contains as few artefacts as possible.

---

Data Structure Documentation

sstvenc_pulseshape

struct sstvenc_pulseshape

Pulse shaper data structure. This should be initialised by calling sstvenc_ps_init.

Definition at line 89 of file pulseshape.h.

Collaboration diagram for sstvenc_pulseshape:

Data Fields
double	amplitude	Peak amplitude of the pulse
uint16_t	fall_sz	Number of samples for the falling pulse.
uint32_t	hold_sz	Number of samples for the hold phase.
double	output	The last computed output of the pulse shaper
uint8_t	phase	Current pulse shaper phase.
uint16_t	rise_sz	Number of samples for the rising pulse.
uint32_t	sample_idx	Sample index for the current phase.
uint32_t	sample_rate	Sample rate for the pulse in Hz

Macro Definition Documentation

SSTVENC_PS_HOLD_TIME_INF

#define SSTVENC_PS_HOLD_TIME_INF   SSTVENC_TS_INFINITE

Hold time = infinite.

Definition at line 83 of file pulseshape.h.

Referenced by sstvenc_ps_compute().

Function Documentation

sstvenc_ps_advance()

void sstvenc_ps_advance

(

struct sstvenc_pulseshape *const

ps

)

Advance the pulse shaper to the next phase, regardless of whether it is finished with the present one. A no-op at the "done" phase.

Parameters

[out]

ps

The pulse shaper being advanced.

Definition at line 56 of file pulseshape.c.

                                                             {
        if (ps->phase < SSTVENC_PS_PHASE_DONE) {
                ps->sample_idx = 0;
                ps->phase++;
        }
}

References sstvenc_pulseshape::phase, sstvenc_pulseshape::sample_idx, and SSTVENC_PS_PHASE_DONE.

Referenced by sstvenc_modulator_next_hold_sample(), sstvenc_ps_compute(), and sstvenc_sequencer_advance().

Here is the caller graph for this function:

sstvenc_ps_compute()

void sstvenc_ps_compute

(

struct sstvenc_pulseshape *const

ps

)

Compute the next pulse shaper value and store it in the output field. A no-op if the sample rate is set to zero or the pulse shaper is done.

The output envelope amplitude can be read from sstvenc_pulseshape::output.

Parameters

[out]

ps

The pulse shaper being computed.

Definition at line 63 of file pulseshape.c.

                                                             {
        ps->sample_idx++;
 
        switch (ps->phase) {
        case SSTVENC_PS_PHASE_INIT:
                ps->phase++;
                /* Fall-thru */
        case SSTVENC_PS_PHASE_RISE:
                if (ps->rise_sz) {
                        /* Compute the raised sine amplitude */
                        ps->output = ps->amplitude
                                     * (1.0
                                        - cos((ps->sample_idx * M_PI)
                                              / (2 * ((double)ps->rise_sz))));
                        if (ps->output > ps->amplitude) {
                                ps->output = ps->amplitude;
                        }
                }
                if (ps->sample_idx > ps->rise_sz) {
                        /* Next phase */
                        sstvenc_ps_advance(ps);
                }
                break;
        case SSTVENC_PS_PHASE_HOLD:
                ps->output = ps->amplitude;
                if ((ps->hold_sz != SSTVENC_PS_HOLD_TIME_INF)
                    && (ps->sample_idx >= ps->hold_sz)) {
                        /* Next phase */
                        sstvenc_ps_advance(ps);
                }
                break;
        case SSTVENC_PS_PHASE_FALL:
                if (ps->fall_sz) {
                        /* Compute the raised sine amplitude */
                        ps->output
                            = ps->amplitude
                              * (1.0
                                 - cos(((ps->fall_sz - ps->sample_idx) * M_PI)
                                       / (2 * ((double)ps->fall_sz))));
 
                        if (ps->output > ps->amplitude) {
                                ps->output = ps->amplitude;
                        }
                }
                if (ps->sample_idx >= ps->fall_sz) {
                        /* Next phase */
                        sstvenc_ps_advance(ps);
                }
                break;
        case SSTVENC_PS_PHASE_DONE:
        default:
                ps->output = 0.0;
                break;
        }
}

References sstvenc_pulseshape::amplitude, sstvenc_pulseshape::fall_sz, sstvenc_pulseshape::hold_sz, sstvenc_pulseshape::output, sstvenc_pulseshape::phase, sstvenc_pulseshape::rise_sz, sstvenc_pulseshape::sample_idx, sstvenc_ps_advance(), SSTVENC_PS_HOLD_TIME_INF, SSTVENC_PS_PHASE_DONE, SSTVENC_PS_PHASE_FALL, SSTVENC_PS_PHASE_HOLD, SSTVENC_PS_PHASE_INIT, and SSTVENC_PS_PHASE_RISE.

Referenced by sstvenc_cw_handle_state_dahspace(), sstvenc_cw_handle_state_ditspace(), sstvenc_cw_handle_state_mark(), sstvenc_modulator_next_fall_sample(), sstvenc_modulator_next_hold_sample(), sstvenc_modulator_next_rise_sample(), sstvenc_psosc_fill_buffer(), and sstvenc_sequencer_compute().

Here is the call graph for this function:

Here is the caller graph for this function:

sstvenc_ps_init()

void sstvenc_ps_init	(	struct sstvenc_pulseshape *const	ps,
		double	amplitude,
		double	rise_time,
		double	hold_time,
		double	fall_time,
		uint32_t	sample_rate,
		uint8_t	time_unit )

Initialise a pulse shaper.

Parameters

[out]	ps	The pulse shaper being initialised
[in]	amplitude	The peak amplitude for the pulse shaper
[in]	rise_time	The rise time in seconds, use 0 to disable rise.
[in]	hold_time	The hold time in seconds, use INFINITY for an indefinite hold.
[in]	fall_time	The fall time in seconds, use 0 to disable fall.
[in]	sample_rate	The sample rate in Hz.
[in]	time_unit	The time unit used to measure rise_time, hold_time and fall_time.

Definition at line 28 of file pulseshape.c.

                                                              {
        uint32_t samples;
 
        ps->amplitude   = amplitude;
        ps->sample_rate = sample_rate;
        ps->output      = 0.0;
 
        samples
            = sstvenc_ts_unit_to_samples(rise_time, sample_rate, time_unit);
        if (samples > UINT16_MAX) {
                ps->rise_sz = UINT16_MAX;
        } else {
                ps->rise_sz = samples;
        }
 
        samples
            = sstvenc_ts_unit_to_samples(fall_time, sample_rate, time_unit);
        if (samples > UINT16_MAX) {
                ps->fall_sz = UINT16_MAX;
        } else {
                ps->fall_sz = samples;
        }
 
        sstvenc_ps_reset(ps, hold_time, time_unit);
}

References sstvenc_pulseshape::amplitude, sstvenc_pulseshape::fall_sz, sstvenc_pulseshape::output, sstvenc_pulseshape::rise_sz, sstvenc_pulseshape::sample_rate, sstvenc_ps_reset(), and sstvenc_ts_unit_to_samples().

Referenced by sstvenc_cw_init(), sstvenc_modulator_init(), and sstvenc_sequencer_begin_tone().

Here is the call graph for this function:

Here is the caller graph for this function:

sstvenc_ps_reset()

void sstvenc_ps_reset	(	struct sstvenc_pulseshape *const	ps,
		double	hold_time,
		uint8_t	time_unit )

Reset the pulse shape state machine with a new hold time, but otherwise identical settings.

Parameters

[in,out]	ps	Pulse shaper context being reset
[in]	hold_time	New hold time given in the time unit specified by time_unit.
[in]	time_unit	Time unit used to measure hold_time. Must be one of the values given in Time-scale units

Definition at line 21 of file pulseshape.c.

                                         {
        uint32_t samples = sstvenc_ts_unit_to_samples(
            hold_time, ps->sample_rate, time_unit);
        sstvenc_ps_reset_samples(ps, samples);
}

References sstvenc_pulseshape::sample_rate, sstvenc_ps_reset_samples(), and sstvenc_ts_unit_to_samples().

Referenced by sstvenc_cw_end_subsym(), sstvenc_cw_end_symbol(), and sstvenc_ps_init().

Here is the call graph for this function:

Here is the caller graph for this function:

sstvenc_ps_reset_samples()

void sstvenc_ps_reset_samples	(	struct sstvenc_pulseshape *const	ps,
		uint32_t	hold_time )

Reset the pulse shape state machine with a new hold time given in samples, but otherwise identical settings.

Parameters

[in,out]	ps	Pulse shaper context being reset
[in]	hold_time	New hold time (given as number of samples).

Definition at line 14 of file pulseshape.c.

                                                                          {
        ps->phase      = SSTVENC_PS_PHASE_INIT;
        ps->hold_sz    = hold_time;
        ps->sample_idx = 0;
}

References sstvenc_pulseshape::hold_sz, sstvenc_pulseshape::phase, sstvenc_pulseshape::sample_idx, and SSTVENC_PS_PHASE_INIT.

Referenced by sstvenc_cw_start_mark(), and sstvenc_ps_reset().

Here is the caller graph for this function:

sstvenc_psosc_fill_buffer()

size_t sstvenc_psosc_fill_buffer	(	struct sstvenc_pulseshape *const	ps,
		struct sstvenc_oscillator *const	osc,
		double *	buffer,
		size_t	buffer_sz )

Fill the given buffer with audio samples from the oscillator shaped with the given pulse shaper. Stop if we run out of buffer space or if the pulse shaper state machine finishes. Return the number of samples generated.

Parameters

[in,out]	ps	Pulse shaper state machine to pull envelope samples from.
[in,out]	osc	Sine wave oscillator. Its amplitude will be modulated by the pulse shaper.
[out]	buffer	Audio buffer to write samples to.
[in]	buffer_sz	Size of the audio buffer in samples.

Returns

Number of samples written to buffer

Definition at line 119 of file pulseshape.c.

                                                                   {
        size_t written_sz = 0;
 
        while ((buffer_sz > 0) && (ps->phase < SSTVENC_PS_PHASE_DONE)) {
                sstvenc_ps_compute(ps);
                osc->amplitude = ps->output;
 
                sstvenc_osc_compute(osc);
                buffer[0] = osc->output;
 
                buffer++;
                buffer_sz--;
 
                written_sz++;
        }
 
        return written_sz;
}

References sstvenc_oscillator::amplitude, sstvenc_oscillator::output, sstvenc_pulseshape::output, sstvenc_pulseshape::phase, sstvenc_osc_compute(), sstvenc_ps_compute(), and SSTVENC_PS_PHASE_DONE.

Here is the call graph for this function: