From 29019f61e52c462b19c69fd82866d182f4ad5d0a Mon Sep 17 00:00:00 2001
From: David Madl <git@abanbytes.eu>
Date: Tue, 19 May 2026 22:40:39 +0200
Subject: [PATCH] fix: remove high-pass prefilter (ssf is already a high-pass)

---
 pasada-lib/include/step_detector.h |  1 -
 pasada-lib/step_detector.cpp       | 19 +------------------
 2 files changed, 1 insertion(+), 19 deletions(-)

diff --git a/pasada-lib/include/step_detector.h b/pasada-lib/include/step_detector.h
index af6dcc3..8662c20 100644
--- a/pasada-lib/include/step_detector.h
+++ b/pasada-lib/include/step_detector.h
@@ -24,7 +24,6 @@ public:
 class StepDetector {
 protected:
     StepListener *listener;
-    IirFilter f_highpass;
     Filt f_neg;
     SsfFilter f_ssf;
     SsfStepDetector f_ssd;
diff --git a/pasada-lib/step_detector.cpp b/pasada-lib/step_detector.cpp
index 1909054..8a8570c 100644
--- a/pasada-lib/step_detector.cpp
+++ b/pasada-lib/step_detector.cpp
@@ -4,24 +4,8 @@
 
 #include "step_detector.h"
 
-// TODO: we are hardcoding filter coefficients for 60 Hz
-// TODO: this is tolerable for 50 Hz
-
-// TODO: check if we can do with floats instead of doubles
-// (check how much the [already bad] accuracy of filtering suffers)
-
-// TODO: in Java, check if delta timestamps effectively match FPS
-// TODO: FPS constant should be passed as argument to C++ (but we keep an FPS define to validate the coefficients)
-
-// Butterworth filter: order=5, fc=0.5, fs=60, btype='highpass'
-static std::vector<double> hpf_taps_b {0.91875845, -4.59379227,  9.18758454, -9.18758454,  4.59379227, -0.91875845};
-static std::vector<double> hpf_taps_a {1.        , -4.83056552,  9.33652742, -9.02545247,  4.36360803, -0.8441171};
-static size_t upslope_width = 4;
-const size_t len_refr = (size_t) (FPS / (MAX_BPM / 60));
-
 StepDetector::StepDetector(double fps, StepListener *listener, bool debug) :
     listener(listener),
-    f_highpass(hpf_taps_b, hpf_taps_a),
     f_neg(1, 0, 0, std::vector<double> {-1.0}),
     f_ssf(fps),
     f_ssd(fps),
@@ -35,8 +19,7 @@ StepDetector::StepDetector(double fps, StepListener *listener, bool debug) :
 
 void StepDetector::filter(std::vector<float> values) {
     // TODO: later on, we should use a vector projection towards gravity
-    auto s0 = (double) values[1]; // take y-axis value for now
-    auto s1 = f_highpass.filter(s0);
+    auto s1 = (double) values[1]; // take y-axis value for now
     auto s2 = f_neg.filter(s1);
     auto s3 = f_ssf.filter(s2);
     auto s4 = f_ssd.filter(s3);