Note Expression Support

Introduction

Note Expression is a new way of event controller editing in host supporting this VST 3.5 feature (like Cubase 6).

With VST 3 Note Expression, the Plug-in is able to break free from the limitations of MIDI controller events by providing access to new VST 3 controller events that circumvent the laws of MIDI and provide articulation information for each individual note (event) in a polyphonic arrangement according to its noteId.

A major limitation of MIDI is the nature of controller information; controllers are only channel messages (Pitch Bend, Modulation,...) and could not be assigned to a specific playing note, with the exception of poly pressure (polyphonic aftertouch) which allows change only for a given pitch (not a given note!).

Articulating each note in a chord individually creates a much more natural feel, just like multiple players playing the same instrument at the same time but each adding his own personality to the notes played.

For example Cubase 6 introduces the first VST 3 Note Expression compatible virtual instrument: HALion Sonic SE. This Plug-in HALion Sonic SE does not only supports "standard" note expression control for Tuning (Pitch), Volume and Pan, it also offers additional custom pre-assigned note expression types of event (kCustomStart in Steinberg::Vst::NoteExpressionTypeIDs).

How does it work ?

The best way to understand how to support note expression from the Plug-in side, is to check out the step by step implementation example below. For more details, check out the Note Expression Synth example included in the SDK.

Step by Step:
We want a mono-timbral (1 channel) instrument Plug-in with 1 event bus and support for the detune (kTuningTypeID) note expression:

1. The instrument Plug-in must have at least one input event bus.

//------------------------------------------------------------------------
tresult PLUGIN_API MyExampleProcessor::initialize (FUnknown* context)
{
   //---always initialize the parent-------
   tresult result = AudioEffect::initialize (context);
   if (result == kResultTrue)
   {
      // we want a Stereo Output
      addAudioOutput (STR16 ("Stereo Output"), SpeakerArr::kStereo);
   
      // create Event In bus (1 bus with only 1 channel)
      addEventInput (STR16 ("Event Input"), 1);
   }
   return result;
}
//------------------------------------------------------------------------


2. The controller must provide the Steinberg::Vst::INoteExpressionController interface, like below:

//-----------------------------------------------------------------------------
class MyExampleController: public EditController, public INoteExpressionController
{
public:
...
   //---from INoteExpressionController
   virtual int32 PLUGIN_API getNoteExpressionCount (int32 busIndex, int16 channel);
   virtual tresult PLUGIN_API getNoteExpressionInfo (int32 busIndex, int16 channel, int32 noteExpressionIndex, NoteExpressionTypeInfo& info);
   virtual tresult PLUGIN_API getNoteExpressionStringByValue (int32 busIndex, int16 channel, NoteExpressionTypeID id, NoteExpressionValue valueNormalized , String128 string);
   virtual tresult PLUGIN_API getNoteExpressionValueByString (int32 busIndex, int16 channel, NoteExpressionTypeID id, const TChar* string, NoteExpressionValue& valueNormalized);
...

   OBJ_METHODS (MyExampleController, EditController)
   DEFINE_INTERFACES
      DEF_INTERFACE (INoteExpressionController)
   END_DEFINE_INTERFACES (EditController)

   REFCOUNT_METHODS(EditController)
...
};
//-----------------------------------------------------------------------------


3. Now we have to implement the Steinberg::Vst::INoteExpressionController interface, in our example Steinberg::Vst::INoteExpressionController::getNoteExpressionCount should return 1 as we only want to support tuning:

//------------------------------------------------------------------------
int32 MyExampleController::getNoteExpressionCount (int32 busIndex, int16 channel)
{
   // we accept only the first bus and 1 channel
   if (busIndex == 0 && channel == 0)
      return 1;
   return 0;
}
//------------------------------------------------------------------------


4. Then we have to implement Steinberg::Vst::INoteExpressionController::getNoteExpressionInfo which describes what note expression the Plug-in supports:

//------------------------------------------------------------------------
tresult PLUGIN_API MyExampleController::getNoteExpressionInfo (int32 busIndex, int16 channel, int32 noteExpressionIndex, 
                     NoteExpressionTypeInfo& info)
{
   // we accept only the first bus and 1 channel and only 1 Note Expression (tuning)
   if (busIndex == 0 && channel == 0 && noteExpressionIndex == 0)
   {
      memset (&info, 0, sizeof (NoteExpressionTypeInfo));

      // set the tuning type
      info.typeId = kTuningTypeID;

      // set some strings
      USTRING ("Tuning").copyTo (info.title, 128);
      USTRING ("Tun").copyTo (info.shortTitle, 128);
      USTRING ("Half Tone").copyTo (info.units, 128);

      info.unitID = -1; // no unit wanted
      info.associatedParameterID = -1; // no associated parameter wanted

      info.flags = NoteExpressionTypeInfo::kIsBipolar; // event is bipolar (centered)

      // for Tuning the convert functions are : plain = 240 * (norm - 0.5); norm = plain / 240 + 0.5;
      // we want to support only +/- one octave
      double kNormTuningOneOctave = 12.0 / 240.0;

      info.valueDesc.minimum = 0.5 - kNormTuningOneOctave;
      info.valueDesc.maximum = 0.5 + kNormTuningOneOctave;
      info.valueDesc.defaultValue = 0.5; // middle of [0, 1] => no detune (240 * (0.5 - 0.5) = 0)
      info.valueDesc.stepCount = 0; // we want continuous (no step)
   
      return kResultTrue;
   }

   return kResultFalse;
}
//------------------------------------------------------------------------


5. For displaying note expression values, we have to implement the conversion functions:

//------------------------------------------------------------------------
tresult PLUGIN_API MyExampleController::getNoteExpressionStringByValue (int32 busIndex, int16 channel, NoteExpressionTypeID id,
                     NoteExpressionValue valueNormalized , String128 string);
{
   // here we use the id (not the index)
   if (busIndex == 0 && channel == 0 && id == kTuningTypeID)   
   {
      // here we have to convert a normalized value to a Tuning string representation
      UString128 wrapper;
      valueNormalized = (240 * valueNormalized) - 120; // compute half Tones
      wrapper.printFloat (valueNormalized, 2);
      wrapper.copyTo (string, 128);
      
      return kResultTrue;
   }

   return kResultFalse;
}
//------------------------------------------------------------------------


//-----------------------------------------------------------------------------
tresult PLUGIN_API MyExampleController::getNoteExpressionValueByString (int32 busIndex, int16 channel, NoteExpressionTypeID id, 
                     const TChar* string, NoteExpressionValue& valueNormalized);
{
   // here we use the id (not the index)
   if (busIndex == 0 && channel == 0 && id == kTuningTypeID)
   {
      // here we have to convert a given tuning string (half Tone) to a normalized value
      String wrapper ((TChar*)string);
      ParamValue tmp;
      if (wrapper.scanFloat (tmp))
      {
         valueNormalized = (tmp + 120) / 240;
         return kResultTrue;
      }
   }

   return kResultFalse;
}
//------------------------------------------------------------------------


6. Last step, in the processor component we have to adapt the process call to interpret the note expression event (Steinberg::Vst::NoteExpressionValueEvent) send from the host to the Plug-in:

//------------------------------------------------------------------------
tresult MyExampleProcessor::process (ProcessData& data)
{
   ....

   // get the input event queue
   IEventList* inputEvents = data.inputEvents;
   if (inputEvents)
   {
      Event e;
      int32 numEvents = inputEvents->getEventCount ();
      
      // for each events check it..
      for (int32 i = 0; i < numEvents; i++)
      {
         if (inputEvents->getEvent (i, e) == kResultTrue)
         {
            switch (e.type)
            {
               //-----------------------
               case Event::kNoteOnEvent:
               {
                  // here a note On, we may need to play something a keep a trace of the e.noteOn.noteId
                  break;
               }
               //-----------------------
               case Event::kNoteOffEvent:
               {
                  // here we have to release the voice associated to this id : e.noteOff.noteId
                  // Note that kNoteExpressionValueEvent event could be send after the note is in released
                  break;
               }
               //-----------------------
               case Event::kNoteExpressionValueEvent:
               {
                  // here are the Note Expression interpretation
                  
                  // we check and use only tuning expression
                  if (e.noteExpressionValue.typeId == kTuningTypeID)
                  {
                     // we have to find the voice which should be change (the note could be in released state)
                     VoiceClass* voice = findVoice (e.noteExpressionValue.noteId);
                     if (voice)
                     {
                        // we apply to it the wanted value (for a given type of note expression (detune, volume....)
                        voice->setNoteExpressionValue (e.noteExpressionValue.typeId, e.noteExpressionValue.value);
                     }
                     // if the associated id is not anymore marked as playing voice (end of release reached) we ignore the Note Expression Event
                  }

                  break;
               }
            }
         }
      }
   }
   ...
}
//------------------------------------------------------------------------



That is it!


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