From 751db481a699d80a1aeec014920f6c972b25b9bd Mon Sep 17 00:00:00 2001
From: Robin Gareus <robin@gareus.org>
Date: Fri, 25 Sep 2020 17:08:21 +0200
Subject: [PATCH] Use linear fades for loop-range cross-fades

The cross-over point of an exponential fade occurs further towards
start of the fade. This increases consistency of cross-fades moving
the cross-over point to the center of the fade.

Also looped material is likely correlated in which a linear fade
is more appropriate.
---
 libs/ardour/ardour/disk_reader.h |  2 +-
 libs/ardour/disk_reader.cc       | 22 +++++++++++++++++++---
 2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/libs/ardour/ardour/disk_reader.h b/libs/ardour/ardour/disk_reader.h
index d9773bbeba..14ca54a07c 100644
--- a/libs/ardour/ardour/disk_reader.h
+++ b/libs/ardour/ardour/disk_reader.h
@@ -181,7 +181,7 @@ protected:
 		Declicker ();
 		~Declicker ();
 
-		void alloc (samplecnt_t sr, bool fadein);
+		void alloc (samplecnt_t sr, bool fadein, bool linear);
 
 		void run (Sample* buf, samplepos_t start, samplepos_t end);
 		void reset (samplepos_t start, samplepos_t end, bool fadein, samplecnt_t sr);
diff --git a/libs/ardour/disk_reader.cc b/libs/ardour/disk_reader.cc
index 95904fa171..607f5fdefc 100644
--- a/libs/ardour/disk_reader.cc
+++ b/libs/ardour/disk_reader.cc
@@ -1643,11 +1643,27 @@ DiskReader::Declicker::~Declicker ()
 }
 
 void
-DiskReader::Declicker::alloc (samplecnt_t sr, bool fadein)
+DiskReader::Declicker::alloc (samplecnt_t sr, bool fadein, bool linear)
 {
 	delete[] vec;
 	vec = new Sample[loop_fade_length];
 
+	if (linear) {
+		if (fadein) {
+			for (samplecnt_t n = 0; n < loop_fade_length; ++n) {
+				vec[n] = n / (float) loop_fade_length;
+			}
+		} else {
+			for (samplecnt_t n = 0; n < loop_fade_length; ++n) {
+				vec[n] = 1.f - n / (float) loop_fade_length;
+			}
+		}
+		fade_length = loop_fade_length - 1;
+		return;
+	}
+
+	/* Exponential fade */
+
 	const float a = 390.f / sr; // ~ 1/100Hz for 40dB
 
 	/* build a psuedo-exponential (linear-volume) shape for the fade */
@@ -1884,8 +1900,8 @@ void
 DiskReader::alloc_loop_declick (samplecnt_t sr)
 {
 	loop_fade_length = lrintf (ceil (-log (GAIN_COEFF_DELTA / 2.) / (390. / sr)));
-	loop_declick_in.alloc (sr, true);
-	loop_declick_out.alloc (sr, false);
+	loop_declick_in.alloc (sr, true, Config->get_loop_fade_choice () == XFadeLoop);
+	loop_declick_out.alloc (sr, false, Config->get_loop_fade_choice () == XFadeLoop);
 }
 
 #undef GAIN_COEFF_DELTA