Remove glitching from the Flanger and Delay plugins

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

@@ -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 );
 }
@@ -57,20 +57,22 @@ 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;
 }
 
 
 
 
+
+
 void StereoDelay::setSampleRate( int sampleRate )
 {
 	if( m_buffer )

plugins/Delay/StereoDelay.h

@@ -52,7 +52,7 @@ class StereoDelay
 	sampleFrame* m_buffer;
 	int m_maxLength;
 	float m_length;
-	int m_index;
+	int m_writeIndex;
 	float m_feedback;
 	float m_maxTime;
 };

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] );

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;
 }
 

plugins/Flanger/MonoDelay.h

@@ -52,7 +52,7 @@ class MonoDelay
 	sample_t* m_buffer;
 	int m_maxLength;
 	float m_length;
-	int m_index;
+	int m_writeIndex;
 	float m_feedback;
 	float m_maxTime;
 };