Filter: add get_cutoff_frequency

libraries/Filter/LowPassFilter.h

@@ -35,6 +35,7 @@ public:
     LowPassFilter();
 
     void set_cutoff_frequency(float time_step, float cutoff_freq);
+    float get_cutoff_frequency() { return _cutoff_hz; }
     void set_time_constant(float time_step, float time_constant);
 
     // apply - Add a new raw value to the filter, retrieve the filtered result
@@ -56,7 +57,8 @@ public:
 private:
     float           _alpha;             // gain value  (like 0.02) applied to each new value
     bool            _base_value_set;    // true if the base value has been set
-    float           _base_value;        // the number of samples in the filter, maxes out at size of the filter
+    float           _base_value;        // filter output
+    float           _cutoff_hz;         // cutoff frequency in hz
 };
 
 // Typedef for convenience (1st argument is the data type, 2nd is a larger datatype to handle overflows, 3rd is buffer size)
@@ -89,6 +91,7 @@ LowPassFilter<T>::LowPassFilter() :
 template <class T>
 void LowPassFilter<T>::set_cutoff_frequency(float time_step, float cutoff_freq)
 {
+    _cutoff_hz = cutoff_freq;
     // avoid divide by zero and allow removing filtering
     if (cutoff_freq <= 0.0f) {
         _alpha = 1.0f;
@@ -96,7 +99,7 @@ void LowPassFilter<T>::set_cutoff_frequency(float time_step, float cutoff_freq)
     }
 
     // calculate alpha
-    float rc = 1/(2*PI*cutoff_freq);
+    float rc = 1/(2*M_PI_F*cutoff_freq);
     _alpha = time_step / (time_step + rc);
 }
 
@@ -105,10 +108,13 @@ void LowPassFilter<T>::set_time_constant(float time_step, float time_constant)
 {
     // avoid divide by zero
     if (time_constant + time_step <= 0.0f) {
+        _cutoff_hz = 0.0f;
         _alpha = 1.0f;
         return;
     }
 
+    _cutoff_hz = 1/(2*M_PI_F*time_constant);
+
     // calculate alpha
     _alpha = time_step / (time_constant + time_step);
 }