From 2343485c1ce2ebb8f6f5c1ecc3e9bdfda603076b Mon Sep 17 00:00:00 2001
From: Robbert van der Helm <mail@robbertvanderhelm.nl>
Date: Sun, 6 Mar 2022 15:33:16 +0100
Subject: [PATCH] Don't do gain compensation in STFT helper

You'll likely want to add some scaling yourself anyways, so this would
just be a wasted operation since the scaling also depends on your window
function.
---
 plugins/examples/stft/src/lib.rs | 14 +++++++-------
 src/util/stft.rs                 | 12 +++++-------
 2 files changed, 12 insertions(+), 14 deletions(-)

diff --git a/plugins/examples/stft/src/lib.rs b/plugins/examples/stft/src/lib.rs
index 1eb79027..8aa0c74b 100644
--- a/plugins/examples/stft/src/lib.rs
+++ b/plugins/examples/stft/src/lib.rs
@@ -72,18 +72,18 @@ impl Plugin for Stft {
         buffer: &mut Buffer,
         _context: &mut impl ProcessContext,
     ) -> ProcessStatus {
+        const GAIN_COMPENSATION: f32 = 2.0 / OVERLAP_TIMES as f32;
         self.stft.process_overlap_add(
             buffer,
             [],
             &self.window_function,
             OVERLAP_TIMES,
-            2.0 / OVERLAP_TIMES as f32, // Gain compensation for the overlap
-            |_channel_idx, _, _block| {
-                // for sample in block {
-                //     // TODO: Use the FFTW bindings and do some STFT operation here instead of
-                //     //       reducing the gain at a 2048 sample latency...
-                //     *sample *= 0.5;
-                // }
+            |_channel_idx, _, block| {
+                for sample in block {
+                    // TODO: Use the FFTW bindings and do some STFT operation here instead of
+                    //       reducing the gain at a 2048 sample latency...
+                    *sample *= GAIN_COMPENSATION;
+                }
             },
         );
 
diff --git a/src/util/stft.rs b/src/util/stft.rs
index ff209f1a..69dd25ea 100644
--- a/src/util/stft.rs
+++ b/src/util/stft.rs
@@ -100,6 +100,9 @@ impl<const NUM_SIDECHAIN_INPUTS: usize> StftHelper<NUM_SIDECHAIN_INPUTS> {
     /// [`ProcessContext::set_latency()`][`crate::prelude::ProcessContext::set_latency()`] in your
     /// plugin's initialization function.
     ///
+    /// This function does not apply any gain compensation for the windowing. You will need to do
+    /// that yoruself depending on your window function and the amount of overlap.
+    ///
     /// For efficiency's sake this function will reuse the same vector for all calls to
     /// `process_cb`. This means you can only access a single channel's worth of windowed data at a
     /// time. The arguments to that function are `process_cb(channel_idx, sidechain_buffer_idx,
@@ -120,7 +123,6 @@ impl<const NUM_SIDECHAIN_INPUTS: usize> StftHelper<NUM_SIDECHAIN_INPUTS> {
         sidechain_buffers: [&Buffer; NUM_SIDECHAIN_INPUTS],
         window_function: &[f32],
         overlap_times: usize,
-        overlap_gain_compensation: f32,
         mut process_cb: F,
     ) where
         F: FnMut(usize, Option<usize>, &mut [f32]),
@@ -227,7 +229,6 @@ impl<const NUM_SIDECHAIN_INPUTS: usize> StftHelper<NUM_SIDECHAIN_INPUTS> {
                         &self.scratch_buffer,
                         self.current_pos,
                         output_ring_buffer,
-                        overlap_gain_compensation,
                     );
                 }
             }
@@ -270,7 +271,6 @@ fn add_scratch_to_ring_buffer(
     scratch_buffer: &[f32],
     current_pos: usize,
     ring_buffer: &mut [f32],
-    gain_compensation: f32,
 ) {
     // TODO: This could also use some SIMD
     let block_size = scratch_buffer.len();
@@ -279,14 +279,12 @@ fn add_scratch_to_ring_buffer(
         .iter()
         .zip(&mut ring_buffer[current_pos..block_size])
     {
-        // TODO: Moving this gain compensation to the window is more efficient, but that makes the
-        //       interface less nice to work with
-        *ring_sample += *scratch_sample * gain_compensation;
+        *ring_sample += *scratch_sample;
     }
     for (scratch_sample, ring_sample) in scratch_buffer[num_copy_before_wrap..block_size]
         .iter()
         .zip(&mut ring_buffer[0..current_pos])
     {
-        *ring_sample += *scratch_sample * gain_compensation;
+        *ring_sample += *scratch_sample;
     }
 }