From ce72dc5f030aa986c8cb052908d9492b9f1bafb9 Mon Sep 17 00:00:00 2001
From: Robbert van der Helm <mail@robbertvanderhelm.nl>
Date: Sun, 24 Jul 2022 18:25:46 +0200
Subject: [PATCH] Fix disabled DC filter behavior

This fixes a NaN from taking the logarithm of zero, and the lower bins
are not actually compressed when this option is disabled. This is useful
when using tiny window sizes as the first bin will span quite a chunk of
the spectrum.
---
 .../src/compressor_bank.rs                    |  3 ++-
 plugins/spectral_compressor/src/lib.rs        | 21 +++++++++++--------
 2 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/plugins/spectral_compressor/src/compressor_bank.rs b/plugins/spectral_compressor/src/compressor_bank.rs
index 73c1d6de..a5cb5ab5 100644
--- a/plugins/spectral_compressor/src/compressor_bank.rs
+++ b/plugins/spectral_compressor/src/compressor_bank.rs
@@ -402,7 +402,8 @@ impl CompressorBank {
         // These 2-log frequencies are needed when updating the compressor parameters, so we'll just
         // precompute them to avoid having to repeat the same expensive computations all the time
         self.log2_freqs.resize(complex_buffer_len, 0.0);
-        for (i, log2_freq) in self.log2_freqs.iter_mut().enumerate() {
+        // The first one should always stay at zero, `0.0f32.log2() == NaN`.
+        for (i, log2_freq) in self.log2_freqs.iter_mut().enumerate().skip(1) {
             let freq = (i as f32 / window_size as f32) * buffer_config.sample_rate;
             *log2_freq = freq.log2();
         }
diff --git a/plugins/spectral_compressor/src/lib.rs b/plugins/spectral_compressor/src/lib.rs
index b9b881b2..a1faf4fe 100644
--- a/plugins/spectral_compressor/src/lib.rs
+++ b/plugins/spectral_compressor/src/lib.rs
@@ -348,10 +348,14 @@ impl Plugin for SpectralCompressor {
         let fft_plan = &mut self.plan_for_order.as_mut().unwrap()
             [self.params.global.window_size_order.value as usize - MIN_WINDOW_ORDER];
         let num_bins = self.complex_fft_buffer.len();
-        // The Hann window function spreads the DC signal out slightly, so we'll clear
-        // all 0-20 Hz bins for this.
-        let highest_dcish_bin_idx =
-            (20.0 / ((self.buffer_config.sample_rate / 2.0) / num_bins as f32)).floor() as usize;
+        // The Hann window function spreads the DC signal out slightly, so we'll clear all 0-20 Hz
+        // bins for this. With small window sizes you probably don't want this as it would result in
+        // a significant low-pass filter. When it's disabled, the DC bin will also be compressed.
+        let first_non_dc_bin_idx = if self.params.global.dc_filter.value {
+            (20.0 / ((self.buffer_config.sample_rate / 2.0) / num_bins as f32)).floor() as usize + 1
+        } else {
+            0
+        };
 
         // The overlap gain compensation is based on a squared Hann window, which will sum perfectly
         // at four times overlap or higher. We'll apply a regular Hann window before the analysis
@@ -395,14 +399,13 @@ impl Plugin for SpectralCompressor {
                     channel_idx,
                     &self.params,
                     overlap_times,
-                    highest_dcish_bin_idx + 1,
+                    first_non_dc_bin_idx,
                 );
 
                 // The DC and other low frequency bins doesn't contain much semantic meaning anymore
-                // after all of this, so it only ends up consuming headroom.
-                if self.params.global.dc_filter.value {
-                    self.complex_fft_buffer[..highest_dcish_bin_idx + 1].fill(Complex32::default());
-                }
+                // after all of this, so it only ends up consuming headroom. If the DC filter is
+                // disabled then this won't do anything.
+                self.complex_fft_buffer[..first_non_dc_bin_idx].fill(Complex32::default());
 
                 // Inverse FFT back into the scratch buffer. This will be added to a ring buffer
                 // which gets written back to the host at a one block delay.