Frequently Asked Questions (FAQ)

Communication

Q: How should I communicate between the 'Processing' and the 'User Interface'?

With the term 'Processing' we mean the code implementing the IAudioProcessor interface: kVstAudioEffectClass component), and with 'User Interface' the editor part (implementing the IEditController: kVstComponentControllerClass component).

Q: I want to implement an audio meter in my user interface. How do I do this?

Processing

Q: How does Audio Processing Bypass work?

In order to implement audio process bypassing, the plug-in can export a parameter which is additionally and exclusively flagged as having the attribute kIsBypass. When the user activates the plug-in bypass in the host, like all parameter changes, this is sent as part of the parameter data passed to the IAudioProcessor::process method.

The implementation of the bypass feature is entirely the responsibility of the plug-in: The IAudioProcessor::process method will continue to be called. The plug-in must take care of artifact-free switching (ramping, parallel processing or algorithm changes) and must also provide a delayed action if your plug-in has a latency.

Q: Must the host deliver valid initialized Audio buffers if the associated bus is deactivated?

In a correctly implemented host, if a input or output bus exists in the host, has become disconnected from the plug-in, the plug-in will receive disconnection information.

Additionally, a plug-in with a disconnected input bus will continue to receive default silence buffers, just as a plug-in with a disconnected output bus will continue to receive default nirvana buffers,

Q: Can the max. sample block size change while the plug-in is processing?

The max. sample block size (maxSamplesPerBlock) can change during the lifetime of a plugin, but NOT while the audio component is active. Therefore max. sample block size (maxSamplesPerBlock) can never change during or between processing calls while the plug-in is active.

If the host changes the max. sample block size it specifically calls the following.

	AudioComponent::setActive (false);
	AudioComponent::setupProcessing (...);
	AudioComponent::setActive (true);

Q: Can the sample rate change while the plug-in is processing?

GUI-Editor

Q: The host doesn't open my plug-in UI, why?

If you are not using VSTGUI, please check that you provide the correct object derived from EditorView or CPlugInView and that you overwrite the function isPlatformTypeSupported ().

Compatibility with VST2.x or VST1

Q: How can I update my VST2 version of my plug-in to a VST3 version and be sure that Cubase will load it instead of my old one?

You have to provide a special UID for your kVstAudioEffectClass and kVstComponentControllerClass components, based on its VST2 UniqueID (4 characters) and its plug-in name like this:

static void convertVST2UID_To_FUID (FUID& newOne, int32 myVST2UID_4Chars, const char* pluginName, bool forControllerUID = false)
{
	char uidString[33];
	
	int32 vstfxid;
	if (forControllerUID)
		vstfxid = (('V' << 16) | ('S' << 8) | 'E');
	else
		vstfxid = (('V' << 16) | ('S' << 8) | 'T');
	
	char vstfxidStr[7] = {0};
	sprintf (vstfxidStr, "%06X", vstfxid);
	
	char uidStr[9] = {0};
	sprintf (uidStr, "%08X", myVST2UID_4Chars);

	strcpy (uidString, vstfxidStr);
	strcat (uidString, uidStr);
			
	char nameidStr[3] = {0};
	size_t len = strlen (pluginName);
	
	// !!!the pluginName has to be lower case!!!!
	for (uint16 i = 0; i <= 8; i++)
	{
		uint8 c = i < len ? pluginName[i] : 0;
		sprintf (nameidStr, "%02X", c);
		strcat (uidString, nameidStr);
	}
	newOne.fromString (uidString);
}

Q: In VST2 the editor was able to access the processing part, named effect, directly. How can I do this in VST3?

Persistence

Q: How does persistence work?

An instantiated plug-in often has state information that must be saved in order to properly re-instantiate that plug-in at a later time. A VST3 plug-in has two states which are saved and reloaded: its component state and its controller state.

The sequencing is the following for saving:

Q: What's the difference between EditController::setComponentState and EditController::setState?

Miscellaneous

Q: How is a normalized value converted to a discrete integer value in VST3?

If you have a parameter with, let's say, three stages (0,1,2), you could convert the normalized value like this:

	int32 plainValue;

	if (normalizedValue < 0.3333333)
	    plainValue = 0;
	else if (normalizedValue < 0.6666666)
	    plainValue = 1;
	else
	    plainValue = 2;		
	

	int32 maxPlain = 2;
	int32 minPlain = 0;
	int32 plainValue;

	int32 nSteps = maxPlain - minPlain + 1;

	float step = 1.f / (float)nSteps;

	if (normalizedValue == 1.)
	    plainValue = maxPlain;
	else
	{
	    int32 i;
	    for (i = 0; i < nSteps; i++)
	    {
	        if (normalizedValue < (i + 1) * step)
	        {
	            plainValue = i + minPlain;				  
	            break;
	        }
	    }
	}

Q: What is the return value tresult?

Almost all VST3 interfaces return a tresult value. This integer value allows to return some errors or success states (not only a boolean value: true or false).
In funknown.h are defined the different possible values.
Be careful when checking this return value because a success return is kResultOk which have the integer value 0:

	// this is WRONG!!!!!
	if (component->setActive (true))
	{
	}

	// this is CORRECT!!!!!
	if (component->setActive (true) == kResultOK)
	{
	}
	// or
	// this is CORRECT too!!!!!
	if (component->setActive (true) != kResultOK)
	{
		// error message....
	}