From 56e3b02de7f67da4b94bbcb504b05c407502b76c Mon Sep 17 00:00:00 2001
From: "Matthias P. Braendli" <matthias.braendli@mpb.li>
Date: Sun, 29 Sep 2024 21:15:31 +0200
Subject: Apply asin to input samples

---
 src/main.rs | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

(limited to 'src/main.rs')

diff --git a/src/main.rs b/src/main.rs
index e35062e..8519158 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -270,10 +270,20 @@ fn main() {
                 }
             }
 
-            // Downmix stereo to mono, apply (v/2 + i16::MAX/2), and normalise to [-1.0; 1.0]
+            // Downmix stereo to mono, apply (v/2 + i16::MAX/2),
+            // normalise to [0.0; 1.0],
+            // take the arcsine to compensate for the phasing,
+            // and divide by PI/2 to normalise to [0.0; 1.0]
+            use std::f32::consts::FRAC_2_PI;
             let buf: Vec<f32> = buf
                 .chunks_exact(2)
-                .map(|v| ((v[0]/2 + v[1]/2)/2 + i16::MAX/2) as f32 / 32768.0)
+                .map(|v| {
+                    let samp = ((v[0]/2 + v[1]/2)/2 + i16::MAX/2) as f32 / 32768.0;
+                    if samp < -1.0 || samp > 1.0 {
+                        panic!("sample normalistion broken")
+                    }
+                    f32::asin(samp) * FRAC_2_PI
+                })
                 .collect();
 
             if let Some(w) = &mut in_debug {
-- 
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