File syn_filter.h¶

FileList > dsp > syn_filter.h

Integer-only digital filters for sensor signal conditioning. More...

#include "../util/syn_qmath.h"
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>

Classes¶

Type	Name
struct	SYN_FilterEMA Exponential moving average filter state.
struct	SYN_FilterFIR FIR filter state (Q16 fixed-point).
struct	SYN_FilterMA Moving average filter state.
struct	SYN_FilterMedian Median filter state.

Public Functions¶

Type	Name
void	syn_filter_ema_init (SYN_FilterEMA * f, uint8_t alpha) Initialize an EMA filter.
void	syn_filter_ema_reset (SYN_FilterEMA * f) Reset the filter to its initial state.
int16_t	syn_filter_ema_update (SYN_FilterEMA * f, int16_t sample) Feed a new sample and get the filtered output.
void	syn_filter_fir_init (SYN_FilterFIR * f, const q16_t * taps, q16_t * history, uint16_t num_taps) Initialize an FIR filter.
void	syn_filter_fir_reset (SYN_FilterFIR * f) Reset FIR filter sample history to 0.
q16_t	syn_filter_fir_update (SYN_FilterFIR * f, q16_t sample) Feed a new Q16 sample and get the FIR filtered output.
void	syn_filter_ma_init (SYN_FilterMA * f, uint8_t window) Initialize a moving average filter.
void	syn_filter_ma_reset (SYN_FilterMA * f) Reset the filter to its initial state.
int16_t	syn_filter_ma_update (SYN_FilterMA * f, int16_t sample) Feed a new sample and get the filtered output.
void	syn_filter_median_init (SYN_FilterMedian * f, uint8_t window) Initialize a median filter.
void	syn_filter_median_reset (SYN_FilterMedian * f) Reset the filter to its initial state.
int16_t	syn_filter_median_update (SYN_FilterMedian * f, int16_t sample) Feed a new sample and get the filtered output.

Macros¶

Type	Name
define	SYN_FILTER_MAX_WINDOW `32`

Detailed Description¶

All filters operate on int16_t values and use no floating-point math. Window backing buffers are caller-provided (no malloc).

** **

Moving Average (MA): Smooth noise, configurable window
Exponential Moving Average (EMA): Low-pass, single coefficient
Median: Impulse noise rejection, small windows only

Public Functions Documentation¶

function syn_filter_ema_init¶

Initialize an EMA filter.

void syn_filter_ema_init (
    SYN_FilterEMA * f,
    uint8_t alpha
)

Parameters:

f Filter instance.
alpha Smoothing factor (0–255). Higher = more responsive. Equivalent to alpha = value/256. Example: 64 ≈ 0.25 (slow), 192 ≈ 0.75 (fast).

function syn_filter_ema_reset¶

Reset the filter to its initial state.

void syn_filter_ema_reset (
    SYN_FilterEMA * f
)

Parameters:

f Filter instance.

function syn_filter_ema_update¶

Feed a new sample and get the filtered output.

int16_t syn_filter_ema_update (
    SYN_FilterEMA * f,
    int16_t sample
)

Parameters:

f Filter instance.
sample New raw sample.

Returns:

Filtered value.

function syn_filter_fir_init¶

Initialize an FIR filter.

void syn_filter_fir_init (
    SYN_FilterFIR * f,
    const q16_t * taps,
    q16_t * history,
    uint16_t num_taps
)

Parameters:

f Filter instance.
taps Array of Q16 filter coefficients.
history Caller-provided Q16 history buffer of size num_taps.
num_taps Number of filter taps.

function syn_filter_fir_reset¶

Reset FIR filter sample history to 0.

void syn_filter_fir_reset (
    SYN_FilterFIR * f
)

Parameters:

f Filter instance.

function syn_filter_fir_update¶

Feed a new Q16 sample and get the FIR filtered output.

q16_t syn_filter_fir_update (
    SYN_FilterFIR * f,
    q16_t sample
)

Parameters:

f Filter instance.
sample New Q16 sample.

Returns:

Filtered output in Q16.

function syn_filter_ma_init¶

Initialize a moving average filter.

void syn_filter_ma_init (
    SYN_FilterMA * f,
    uint8_t window
)

Parameters:

f Filter instance.
window Window size (must be <= SYN_FILTER_MAX_WINDOW).

function syn_filter_ma_reset¶

Reset the filter to its initial state.

void syn_filter_ma_reset (
    SYN_FilterMA * f
)

Parameters:

f Filter instance.

function syn_filter_ma_update¶

Feed a new sample and get the filtered output.

int16_t syn_filter_ma_update (
    SYN_FilterMA * f,
    int16_t sample
)

Parameters:

f Filter instance.
sample New raw sample.

Returns:

Filtered value (average of the last window samples).

function syn_filter_median_init¶

Initialize a median filter.

void syn_filter_median_init (
    SYN_FilterMedian * f,
    uint8_t window
)

Parameters:

f Filter instance.
window Window size (should be odd for a true median; must be <= SYN_FILTER_MAX_WINDOW).

function syn_filter_median_reset¶

Reset the filter to its initial state.

void syn_filter_median_reset (
    SYN_FilterMedian * f
)

Parameters:

f Filter instance.

function syn_filter_median_update¶

Feed a new sample and get the filtered output.

int16_t syn_filter_median_update (
    SYN_FilterMedian * f,
    int16_t sample
)

Parameters:

f Filter instance.
sample New raw sample.

Returns:

Median of the last window samples.

Macro Definition Documentation¶

define SYN_FILTER_MAX_WINDOW¶

#define SYN_FILTER_MAX_WINDOW `32`

Maximum window size for moving average and median filters.

The documentation for this class was generated from the following file src/syntropic/dsp/syn_filter.h