From 8fbdc43ce3562013deeb6f80c9828e093c42db76 Mon Sep 17 00:00:00 2001
From: Robbert van der Helm <mail@robbertvanderhelm.nl>
Date: Fri, 22 Jul 2022 23:22:39 +0200
Subject: [PATCH] Fix the high frequency rolloff

---
 .../spectral_compressor/src/compressor_bank.rs   | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/plugins/spectral_compressor/src/compressor_bank.rs b/plugins/spectral_compressor/src/compressor_bank.rs
index 50480e7d..e3a92d79 100644
--- a/plugins/spectral_compressor/src/compressor_bank.rs
+++ b/plugins/spectral_compressor/src/compressor_bank.rs
@@ -557,7 +557,7 @@ impl CompressorBank {
             // If the high-frequency rolloff is enabled then higher frequency bins will have their
             // ratios reduced to reduce harshness. This follows the octave scale.
             let target_ratio_recip = compressor.downwards_ratio.value.recip();
-            if high_freq_ratio_rolloff == 1.0 {
+            if high_freq_ratio_rolloff == 0.0 {
                 self.downwards_ratio_recips.fill(target_ratio_recip);
             } else {
                 for (log2_freq, ratio) in self
@@ -565,11 +565,11 @@ impl CompressorBank {
                     .iter()
                     .zip(self.downwards_ratio_recips.iter_mut())
                 {
-                    // This is scaled by octaves since we're calculating this in log space
                     let octave_fraction = log2_freq / log2_nyquist_freq;
-                    // Division because we're dealing with the reciprocal here
-                    *ratio =
-                        target_ratio_recip / (1.0 - (octave_fraction * high_freq_ratio_rolloff));
+                    let rolloff_t = octave_fraction * high_freq_ratio_rolloff;
+                    // If the octave fraction times the rolloff amount is high, then this should get
+                    // closer to `high_freq_ratio_rolloff` (which is in [0, 1]).
+                    *ratio = (target_ratio_recip * (1.0 - rolloff_t)) + rolloff_t;
                 }
             }
         }
@@ -580,7 +580,7 @@ impl CompressorBank {
             .is_ok()
         {
             let target_ratio_recip = compressor.upwards_ratio.value.recip();
-            if high_freq_ratio_rolloff == 1.0 {
+            if high_freq_ratio_rolloff == 0.0 {
                 self.upwards_ratio_recips.fill(target_ratio_recip);
             } else {
                 for (log2_freq, ratio) in self
@@ -589,8 +589,8 @@ impl CompressorBank {
                     .zip(self.upwards_ratio_recips.iter_mut())
                 {
                     let octave_fraction = log2_freq / log2_nyquist_freq;
-                    *ratio =
-                        target_ratio_recip / (1.0 - (octave_fraction * high_freq_ratio_rolloff));
+                    let rolloff_t = octave_fraction * high_freq_ratio_rolloff;
+                    *ratio = (target_ratio_recip * (1.0 - rolloff_t)) + rolloff_t;
                 }
             }
         }