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Precompute k for PT1 filter #6321

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Merged
DzikuVx merged 3 commits into from
Dec 24, 2020
Merged

Precompute k for PT1 filter #6321

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28448bd
Precompute k for PT1 filter
DzikuVx Nov 19, 2020
1b4c517
Parameter rename
DzikuVx Nov 19, 2020
97bb2b9
Merge remote-tracking branch 'origin/master' into dzikuvx-pt1-filter-…
DzikuVx Dec 4, 2020
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6 changes: 4 additions & 2 deletions src/main/common/filter.c
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Original file line number Diff line number Diff line change
Expand Up @@ -54,6 +54,7 @@ void pt1FilterInitRC(pt1Filter_t *filter, float tau, float dT)
filter->state = 0.0f;
filter->RC = tau;
filter->dT = dT;
filter->alpha = filter->dT / (filter->RC + filter->dT);
}

void pt1FilterInit(pt1Filter_t *filter, float f_cut, float dT)
Expand All @@ -71,7 +72,7 @@ float pt1FilterGetLastOutput(pt1Filter_t *filter) {

float FAST_CODE NOINLINE pt1FilterApply(pt1Filter_t *filter, float input)
{
filter->state = filter->state + filter->dT / (filter->RC + filter->dT) * (input - filter->state);
filter->state = filter->state + filter->alpha * (input - filter->state);
return filter->state;
}

Expand All @@ -90,7 +91,8 @@ float FAST_CODE NOINLINE pt1FilterApply4(pt1Filter_t *filter, float input, float
}

filter->dT = dT; // cache latest dT for possible use in pt1FilterApply
filter->state = filter->state + dT / (filter->RC + dT) * (input - filter->state);
filter->alpha = filter->dT / (filter->RC + filter->dT);
filter->state = filter->state + filter->alpha * (input - filter->state);
return filter->state;
}

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1 change: 1 addition & 0 deletions src/main/common/filter.h
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Expand Up @@ -25,6 +25,7 @@ typedef struct pt1Filter_s {
float state;
float RC;
float dT;
float alpha;
} pt1Filter_t;

/* this holds the data required to update samples thru a filter */
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