Distortion with chorus - c++

Question

I am new to plug in Development and C++. I was trying to write a chorus plug in using XCode Audio Unit Template. However, when I test the plug in with a sine wave I can hear some mild distortion. I believe I did something wrong with the interpolation technique I am using even though I went through it a thousand times and could not figure out what I did wrong. Here is the code I have written that includes the important parts of the audio unit:
private: //state variables...
enum {kWaveArraySize = 2000}; //number of points in the LFO sine array to hold the points
float mSine[kWaveArraySize];
float *waveArrayPointer; //pointer to point in the array Variable to hold Sampling Rate
Float32 SR;
long mSamplesProcessed; //variable to keep track of samples processed
enum {sampleLimit = (int)10E6}; //limit to reset sine wave
float mCurrentScale, mNextScale; //scaling factor for the LFO sine
TAUBuffer<Float32> Buffer; //circular buffer
Float32 rawIndex; //raw read Index
UInt32 ReadIndex, NextIndex; //the Read Index and the sample after the Read Index for Linear Interpolation
UInt32 WriteIndex; //the Write Index
UInt32 BufferSize; //Size of Buffer
UInt32 MaxBufferSize; //Allocated Number of Samples
Float32 DelayTime; //Delay Time going to be calculated according to LFO
Float32 inputSample, outputSample,
freq, Depth, //Variables to hold the frequency of the LFO and Depth parameter
samplesPerCycle, //number of samples per LFO cycle
InterpOutput, //interpolated output variable
fracDelay, DryValue, WetValue; //fractional Delay, Dry and Wet value variables
VibratoUnit::VibratoUnitKernel::VibratoUnitKernel (AUEffectBase *inAudioUnit) : AUKernelBase (inAudioUnit),
mSamplesProcessed(0), mCurrentScale(0)
{
for (int i = 0; i<kWaveArraySize; ++i) //loop to calculate one cycle of LFO
{
double radians = i * 2.0 * pi / kWaveArraySize;
mSine[i] = (sin(radians) + 1.0) * 0.5;
}
SR = GetSampleRate();
BufferSize = SR;
MaxBufferSize = BufferSize + 20;
Buffer.AllocateClear(MaxBufferSize);
ReadIndex = MaxBufferSize - 1;
WriteIndex = MaxBufferSize - 1; //Give both ReadIndex and WriteIndex a Value outside the buffer so they would be reset to 0 in the process method
void VibratoUnit::VibratoUnitKernel::Reset() //Reset and clear
{
mCurrentScale = 0;
mSamplesProcessed = 0;
Buffer.Clear();
}
//------------------PROCESS METHOD-----------------------//
void VibratoUnit::VibratoUnitKernel::Process( const Float32 *inSourceP,
Float32 *inDestP,
UInt32 inFramesToProcess,
UInt32 inNumChannels,
bool &ioSilence )
{
UInt32 nSampleFrames = inFramesToProcess;
const Float32 *sourceP = inSourceP;
Float32 *destP = inDestP;
freq = GetParameter(kParamFreq);
Depth = GetParameter(kParamDepth);
Depth = (SR/1000.0)*Depth;
WetValue = GetParameter(kParamDryWet);
DryValue = 1.0 - WetValue;
waveArrayPointer = &mSine[0];
samplesPerCycle = SR/freq;
mNextScale = kWaveArraySize/samplesPerCycle;
//----processing loop----//
while (nSampleFrames-- > 0) {
int index = static_cast<long> (mSamplesProcessed * mCurrentScale)%kWaveArraySize; //Find index for in the LFO wave table
if ((mNextScale != mCurrentScale) && (index == 0))
{
mCurrentScale = mNextScale;
mSamplesProcessed = 0; //change LFO in 0 crossing
}
if ((mSamplesProcessed >= sampleLimit) && (index == 0))
{
mSamplesProcessed = 0; // reset samples processed
}
if (WriteIndex >= BufferSize) //reset write Index if goes outside the buffer
{
WriteIndex = 0;
}
inputSample = *sourceP;
sourceP += inNumChannels;
DelayTime = waveArrayPointer[index]; //receive raw sine value between 0 and 1
DelayTime = (Depth*DelayTime)+Depth; //calculate delay value according to sine wave
rawIndex = WriteIndex - DelayTime; //calculate rawIndex relative to the write Index position
if (rawIndex < 0) {
rawIndex = BufferSize + rawIndex;
}
ReadIndex = (UInt32)rawIndex; //calculate readIndex according to rawIndex position
fracDelay = DelayTime - (UInt32)DelayTime; //calculate fractional delay time
NextIndex = ReadIndex + 1; //for interpolation
if (NextIndex >= BufferSize) //bounds checking
{
NextIndex = 0;
}
InterpOutput = (fracDelay*Buffer[ReadIndex]) + ((1.0-fracDelay)*Buffer[NextIndex]); //calculate interpolated value
Buffer[ReadIndex] = InterpOutput; //write the interpolated output to buffer
Buffer[WriteIndex] = inputSample; //write inputsample to buffer
outputSample = (Buffer[ReadIndex]*WetValue) + (inputSample * DryValue); //read output sample from buffer
WriteIndex++; //increment writeIndex
mSamplesProcessed++; //increment samplesprocessed
*destP = outputSample;
destP += inNumChannels;
}
}
Thank you for your help in advance.