From bddd26d5571bf984e50ccc59b245d646b90b2c52 Mon Sep 17 00:00:00 2001
From: Jared Boone <jboone@earfeast.com>
Date: Sun, 20 Dec 2015 13:31:00 -0800
Subject: [PATCH] Perform frequency-domain windowing of spectrum.

Reduces sidelobes a bit, improves apparent resolution. Avoids windowing (more RAM and CPU) in baseband.
---
 firmware/baseband/spectrum_collector.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/firmware/baseband/spectrum_collector.cpp b/firmware/baseband/spectrum_collector.cpp
index e344a0f5..dacf45ab 100644
--- a/firmware/baseband/spectrum_collector.cpp
+++ b/firmware/baseband/spectrum_collector.cpp
@@ -69,7 +69,10 @@ void SpectrumCollector::update() {
 
 		ChannelSpectrumMessage spectrum_message;
 		for(size_t i=0; i<spectrum_message.spectrum.db.size(); i++) {
-			const auto mag2 = magnitude_squared(channel_spectrum[i]);
+			// Three point Hamming window.
+			const auto corrected_sample = channel_spectrum[i] * 0.54f
+				+ (channel_spectrum[(i-1) & 0xff] + channel_spectrum[(i+1) & 0xff]) * -0.23f;
+			const auto mag2 = magnitude_squared(corrected_sample);
 			const float db = complex16_mag_squared_to_dbv_norm(mag2);
 			constexpr float mag_scale = 5.0f;
 			const unsigned int v = (db * mag_scale) + 255.0f;