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).
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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