From dd49bd9e7fb6661c34afbeb5ac0aba80980dee61 Mon Sep 17 00:00:00 2001
From: Robbert van der Helm <mail@robbertvanderhelm.nl>
Date: Mon, 25 Jul 2022 15:56:30 +0200
Subject: [PATCH] Move knee scaling factor to a function

---
 plugins/spectral_compressor/src/compressor_bank.rs | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/plugins/spectral_compressor/src/compressor_bank.rs b/plugins/spectral_compressor/src/compressor_bank.rs
index 68a0e407..dd37c695 100644
--- a/plugins/spectral_compressor/src/compressor_bank.rs
+++ b/plugins/spectral_compressor/src/compressor_bank.rs
@@ -601,11 +601,11 @@ impl CompressorBank {
         // bandwidths, the middle values needs to be pushed more towards the post-knee threshold
         // than with lower knee values. These scaling factors are used as exponents.
         let downwards_knee_scaling_factor =
-            ((params.compressors.downwards.knee_width_db.value * 2.0) + 2.0).log2() - 1.0;
+            compute_knee_scaling_factor(params.compressors.downwards.knee_width_db.value);
         // Note the square root here, since the curve needs to go the other way for the upwards
-        // version.
+        // version
         let upwards_knee_scaling_factor =
-            (((params.compressors.upwards.knee_width_db.value * 2.0) + 2.0).log2() - 1.0).sqrt();
+            compute_knee_scaling_factor(params.compressors.upwards.knee_width_db.value).sqrt();
 
         // Is this what they mean by zip and and ship it?
         let downwards_knees = self
@@ -804,6 +804,13 @@ impl CompressorBank {
     }
 }
 
+/// Get the knee scaling factor for converting a linear `[0, 1]` knee range into the correct curve
+/// for the soft knee. This is used to blend between compression at the knee start to compression at
+/// the actual threshold. For upwards compression this needs an additional square root.
+fn compute_knee_scaling_factor(downwards_knee_width_db: f32) -> f32 {
+    ((downwards_knee_width_db * 2.0) + 2.0).log2() - 1.0
+}
+
 /// Get the compression scaling factor for downwards compression with the supplied parameters. The
 /// input signal can be multiplied by this factor to get the compressed output signal. All
 /// parameters are linear gain values.