Audio distorted with VST plugin - c++

Question

I had to plug into a pre-existing software, managing ASIO audio streams, a simple VST host. Despite of lack of some documentation, I managed to do so however once I load the plugin I get a badly distorted audio signal back.
The VST I'm using works properly (with other VST Hosts) so it's probably some kind of bug in the code I made, however when I disable the "PROCESS" from the plugin (my stream goes through the plugin, it simply does not get processed) it gets back as I sent without any noise or distortion on it.
One thing I'm slightly concerned about is the type of the data used as the ASIO driver fills an __int32 buffer while the plugins wants some float buffer.
That's really depressing as I reviewed zillions of times my code and it seems to be fine.
Here is the code of the class I'm using; please note that some numbers are temporarily hard-coded to help debugging.
VSTPlugIn::VSTPlugIn(const char* fullDirectoryName, const char* ID)
: plugin(NULL)
, blocksize(128) // TODO
, sampleRate(44100.0F) // TODO
, hostID(ID)
{
this->LoadPlugin(fullDirectoryName);
this->ConfigurePluginCallbacks();
this->StartPlugin();
out = new float*[2];
for (int i = 0; i < 2; ++i)
{
out[i] = new float[128];
memset(out[i], 0, 128);
}
}
void VSTPlugIn::LoadPlugin(const char* path)
{
HMODULE modulePtr = LoadLibrary(path);
if(modulePtr == NULL)
{
printf("Failed trying to load VST from '%s', error %d\n", path, GetLastError());
plugin = NULL;
}
// vst 2.4 export name
vstPluginFuncPtr mainEntryPoint = (vstPluginFuncPtr)GetProcAddress(modulePtr, "VSTPluginMain");
// if "VSTPluginMain" was not found, search for "main" (backwards compatibility mode)
if(!mainEntryPoint)
{
mainEntryPoint = (vstPluginFuncPtr)GetProcAddress(modulePtr, "main");
}
// Instantiate the plugin
plugin = mainEntryPoint(hostCallback);
}
void VSTPlugIn::ConfigurePluginCallbacks()
{
// Check plugin's magic number
// If incorrect, then the file either was not loaded properly, is not a
// real VST plugin, or is otherwise corrupt.
if(plugin->magic != kEffectMagic)
{
printf("Plugin's magic number is bad. Plugin will be discarded\n");
plugin = NULL;
}
// Create dispatcher handle
this->dispatcher = (dispatcherFuncPtr)(plugin->dispatcher);
// Set up plugin callback functions
plugin->getParameter = (getParameterFuncPtr)plugin->getParameter;
plugin->processReplacing = (processFuncPtr)plugin->processReplacing;
plugin->setParameter = (setParameterFuncPtr)plugin->setParameter;
}
void VSTPlugIn::StartPlugin()
{
// Set some default properties
dispatcher(plugin, effOpen, 0, 0, NULL, 0);
dispatcher(plugin, effSetSampleRate, 0, 0, NULL, sampleRate);
dispatcher(plugin, effSetBlockSize, 0, blocksize, NULL, 0.0f);
this->ResumePlugin();
}
void VSTPlugIn::ResumePlugin()
{
dispatcher(plugin, effMainsChanged, 0, 1, NULL, 0.0f);
}
void VSTPlugIn::SuspendPlugin()
{
dispatcher(plugin, effMainsChanged, 0, 0, NULL, 0.0f);
}
void VSTPlugIn::ProcessAudio(float** inputs, float** outputs, long numFrames)
{
plugin->processReplacing(plugin, inputs, out, 128);
memcpy(outputs, out, sizeof(float) * 128);
}
EDIT: Here's the code I use to interface my sw with the VST Host
// Copying the outer buffer in the inner container
for(unsigned i = 0; i < bufferLenght; i++)
{
float f;
f = ((float) buff[i]) / (float) std::numeric_limits<int>::max()
if( f > 1 ) f = 1;
if( f < -1 ) f = -1;
samples[0][i] = f;
}
// DO JOB
for(auto it = inserts.begin(); it != inserts.end(); ++it)
{
(*it)->ProcessAudio(samples, samples, bufferLenght);
}
// Copying the result back into the buffer
for(unsigned i = 0; i < bufferLenght; i++)
{
float f = samples[0][i];
int intval;
f = f * std::numeric_limits<int>::max();
if( f > std::numeric_limits<int>::max() ) f = std::numeric_limits<int>::max();
if( f < std::numeric_limits<int>::min() ) f = std::numeric_limits<int>::min();
intval = (int) f;
buff[i] = intval;
}
where "buff" is defined as "__int32* buff"

Answer 1

I'm guessing that when you call f = std::numeric_limits<int>::max() (and the related min() case on the line below), this might cause overflow. Have you tried f = std::numeric_limits<int>::max() - 1?
Same goes for the code snippit above with f = ((float) buff[i]) / (float) std::numeric_limits<int>::max()... I'd also subtract one there to avoid a potential overflow later on.