diff --git a/pasada-lib/include/step_detector.h b/pasada-lib/include/step_detector.h
index b8999e3..c1f0aca 100644
--- a/pasada-lib/include/step_detector.h
+++ b/pasada-lib/include/step_detector.h
@@ -12,8 +12,8 @@
 
 class StepListener {
 public:
-    virtual ~StepListener() {}
-    virtual void playBeat() = 0;
+    virtual ~StepListener() = default;
+    virtual void playBeat(double t) = 0;
 };
 
 /** mean-filter the gravity vector, then take acceleration downwards */
@@ -60,10 +60,14 @@ public:
      * @param debug collect debug buffers (used in unit tests)
      */
     StepDetector(double fps, StepListener *listener, bool debug = false);
-    /** filter using raw accel samples (unevenly spaced and 3-dimensional) */
+    /**
+     * Push raw accelerometer values (unevenly sampled and 3-dimensional).
+     * @param ts timestamp in ns
+     * @param values acceleration values for x,y,z
+     */
     void filter(double ts, std::vector<float> values);
     /** filter using scalar accel samples in \vec{e_g} direction */
-    void filter_a(double s1);
+    void filter_a(double t, double s1);
     std::vector<double> getBufSsd();
     std::vector<double> getBufSqi();
     std::vector<double> getBufOut();
@@ -75,4 +79,4 @@ public:
     double primeFilters(double fps, std::vector<double> sig);
 };
 
-#endif //PASADASUPERPROJECT_STEP_DETECTOR_H
\ No newline at end of file
+#endif //PASADASUPERPROJECT_STEP_DETECTOR_H
diff --git a/pasada-lib/step_detector.cpp b/pasada-lib/step_detector.cpp
index dd4480a..5e823c4 100644
--- a/pasada-lib/step_detector.cpp
+++ b/pasada-lib/step_detector.cpp
@@ -65,11 +65,11 @@ void StepDetector::filter(double ts, std::vector<float> values) {
         // gravity filtering
         double a = f_grav.filter(samp);
         // pass on accel sample
-        filter_a(a);
+        filter_a(ts, a);
     }
 }
 
-void StepDetector::filter_a(double s2) {
+void StepDetector::filter_a(double ts, double s2) {
     auto s3 = f_ssf.filter(s2);
     auto s4 = f_ssd.filter(s3);
     auto q5 = f_sqi.filter(s2, s3, s4);
@@ -80,7 +80,7 @@ void StepDetector::filter_a(double s2) {
     }
     // is step, step quality is OK, and we have a listener?
     if(s4 > 0.0 && q5 > 0.0 && listener != nullptr) {
-        listener->playBeat();
+        listener->playBeat(ts / 1e9);
     }
 }