From b432707b9beba0bee1e37281bfa1c5e98e977172 Mon Sep 17 00:00:00 2001
From: Dave French <dave.french3@googlemail.com>
Date: Wed, 17 May 2017 11:18:47 +0100
Subject: [PATCH] Remove glitching from the Flanger and Delay plugins (#3524)

The previous delay code was incorrectly not utalising the whole buffer, causing glitches when
incressing the delay time, due to outputting incorrect data, This was apparent when using the
lfo in the Delay and Flanger plugins.

This has been rectified. The read index is now offset from the write index. and the complete buffer is used in a circular fashon.

Flanger - resolved issue where the lfo could create negative delay lengths
---
 plugins/Delay/StereoDelay.cpp     | 18 ++++++++++--------
 plugins/Delay/StereoDelay.h       |  2 +-
 plugins/Flanger/FlangerEffect.cpp |  4 ++--
 plugins/Flanger/MonoDelay.cpp     | 12 ++++++------
 plugins/Flanger/MonoDelay.h       |  2 +-
 5 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/plugins/Delay/StereoDelay.cpp b/plugins/Delay/StereoDelay.cpp
index 327dfda03..d25f6b52b 100644
--- a/plugins/Delay/StereoDelay.cpp
+++ b/plugins/Delay/StereoDelay.cpp
@@ -36,7 +36,7 @@ StereoDelay::StereoDelay( int maxTime, int sampleRate )
 	m_maxLength = maxTime * sampleRate;
 	m_length = m_maxLength;
 
-	m_index = 0;
+	m_writeIndex = 0;
 	m_feedback = 0.0f;
 	setSampleRate( sampleRate );
 }
@@ -57,13 +57,13 @@ StereoDelay::~StereoDelay()
 
 void StereoDelay::tick( sampleFrame frame )
 {
-	m_index = ( int )m_length > 0
-			? ( m_index + 1 ) % ( int ) m_length
-			: m_index;
-	float lOut = m_buffer[ m_index ][ 0 ];
-	float rOut = m_buffer[ m_index ] [1 ];
-	m_buffer[ m_index ][ 0 ] = frame[ 0 ] + ( lOut * m_feedback );
-	m_buffer[ m_index ][ 1 ] = frame[ 1 ] + ( rOut * m_feedback );
+	m_writeIndex = ( m_writeIndex + 1 ) % ( int )m_maxLength;
+	int readIndex = m_writeIndex - m_length;
+	if (readIndex < 0 ) { readIndex += m_maxLength; }
+	float lOut = m_buffer[ readIndex ][ 0 ];
+	float rOut = m_buffer[ readIndex ] [1 ];
+	m_buffer[ m_writeIndex ][ 0 ] = frame[ 0 ] + ( lOut * m_feedback );
+	m_buffer[ m_writeIndex ][ 1 ] = frame[ 1 ] + ( rOut * m_feedback );
 	frame[ 0 ] = lOut;
 	frame[ 1 ] = rOut;
 }
@@ -71,6 +71,8 @@ void StereoDelay::tick( sampleFrame frame )
 
 
 
+
+
 void StereoDelay::setSampleRate( int sampleRate )
 {
 	if( m_buffer )
diff --git a/plugins/Delay/StereoDelay.h b/plugins/Delay/StereoDelay.h
index 4886149dc..a0dbdc220 100644
--- a/plugins/Delay/StereoDelay.h
+++ b/plugins/Delay/StereoDelay.h
@@ -52,7 +52,7 @@ private:
 	sampleFrame* m_buffer;
 	int m_maxLength;
 	float m_length;
-	int m_index;
+	int m_writeIndex;
 	float m_feedback;
 	float m_maxTime;
 };
diff --git a/plugins/Flanger/FlangerEffect.cpp b/plugins/Flanger/FlangerEffect.cpp
index f9d55bb60..33ad8081b 100644
--- a/plugins/Flanger/FlangerEffect.cpp
+++ b/plugins/Flanger/FlangerEffect.cpp
@@ -107,8 +107,8 @@ bool FlangerEffect::processAudioBuffer( sampleFrame *buf, const fpp_t frames )
 		dryS[0] = buf[f][0];
 		dryS[1] = buf[f][1];
 		m_lfo->tick(&leftLfo, &rightLfo);
-		m_lDelay->setLength( ( float )length + ( amplitude * leftLfo ) );
-		m_rDelay->setLength( ( float )length+ ( amplitude * rightLfo ) );
+		m_lDelay->setLength( ( float )length + amplitude * (leftLfo+1.0)  );
+		m_rDelay->setLength( ( float )length + amplitude * (rightLfo+1.0)  );
 		if(invertFeedback)
 		{
 			m_lDelay->tick( &buf[f][1] );
diff --git a/plugins/Flanger/MonoDelay.cpp b/plugins/Flanger/MonoDelay.cpp
index 534f0bcf8..fc63d57d1 100644
--- a/plugins/Flanger/MonoDelay.cpp
+++ b/plugins/Flanger/MonoDelay.cpp
@@ -34,7 +34,7 @@ MonoDelay::MonoDelay( int maxTime , int sampleRate )
 	m_maxLength = maxTime * sampleRate;
 	m_length = m_maxLength;
 
-	m_index = 0;
+	m_writeIndex = 0;
 	m_feedback = 0.0f;
 	setSampleRate( sampleRate );
 }
@@ -54,11 +54,11 @@ MonoDelay::~MonoDelay()
 
 void MonoDelay::tick( sample_t* sample )
 {
-	m_index = ( int )m_length > 0
-			? ( m_index + 1 ) % ( int )m_length
-			: m_index;
-	float out = m_buffer[ m_index ];
-	m_buffer[ m_index ] = *sample + ( out * m_feedback );
+	m_writeIndex = ( m_writeIndex + 1 ) % ( int )m_maxLength;
+	int readIndex = m_writeIndex - m_length;
+	if (readIndex < 0 ) { readIndex += m_maxLength; }
+	float out = m_buffer[ readIndex ];
+	m_buffer[ m_writeIndex ] = *sample + ( out * m_feedback );
 	*sample = out;
 }
 
diff --git a/plugins/Flanger/MonoDelay.h b/plugins/Flanger/MonoDelay.h
index 8b06bff1b..52898bfe4 100644
--- a/plugins/Flanger/MonoDelay.h
+++ b/plugins/Flanger/MonoDelay.h
@@ -52,7 +52,7 @@ private:
 	sample_t* m_buffer;
 	int m_maxLength;
 	float m_length;
-	int m_index;
+	int m_writeIndex;
 	float m_feedback;
 	float m_maxTime;
 };