From bab8efec1b363114247320461455f2c2010c92f5 Mon Sep 17 00:00:00 2001
From: Ruben Noroian <rubennoro>
Date: Sun, 24 Nov 2024 14:42:40 -0500
Subject: [PATCH] high pass filter implementation

---
 middleware/include/high_pass.h |  8 ++++++
 middleware/src/high_pass.c     | 52 ++++++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+)
 create mode 100644 middleware/include/high_pass.h
 create mode 100644 middleware/src/high_pass.c

diff --git a/middleware/include/high_pass.h b/middleware/include/high_pass.h
new file mode 100644
index 0000000..8abc59b
--- /dev/null
+++ b/middleware/include/high_pass.h
@@ -0,0 +1,8 @@
+#ifndef HIGH_PASS_H
+#define HIGH_PASS_H
+
+#include <stdio.h>
+
+int high_pass(int alpha, int scale);
+
+#endif
diff --git a/middleware/src/high_pass.c b/middleware/src/high_pass.c
new file mode 100644
index 0000000..b5e6b5d
--- /dev/null
+++ b/middleware/src/high_pass.c
@@ -0,0 +1,52 @@
+/*
+Understanding High-Pass Filter Implementation
+
+Goal is to customize the cutoff frequency/strength 
+
+One style:
+-alpha factor  -> smoothing factor used to make the changes smoother
+-scale factor  -> scales the output given by algo
+these two params correlate to strength
+
+Or user could pass desired cutoff frequency and that would be used
+
+Algorithm:
+1. first possibility
+output = alpha * last_output + (1-alpha) * input
+
+output = alpha * last_output + alpha * (avg - prev_avg)
+
+*/
+#include "high_pass.h"
+
+//Samples can be modified
+#define SAMPLES 12
+
+//Scale Var allows adjustment of output strength
+//Alpha Var controls weight of prev input & sum difference
+float high_pass(int alpha, int scale)
+{
+	static float buffer[SAMPLES] = { 0 }; //initialize changing buffer
+	static int index = 0;
+	static float prev_sum = 0.0;
+
+	//buffer[index] = freq; //-> adding the freq input into the
+
+	index = (index + 1) % SAMPLES;
+
+	float sum = 0.0;
+
+	//Iterates through all indices
+	for (int i = 0; i < SAMPLES; i++) {
+		sum += buffer[i];
+	}
+
+	//Algorithm
+	//
+	float output =
+		scale * (alpha * buffer[index - 1] + alpha * (sum - prev_sum));
+
+	prev_sum = sum; //updates the prev_sum
+
+	return output;
+}