standalone parameters changes and cc handling

[nniippsseell-source]

In my plugin, for the standalone version, i want to handle MIDI Control Changes.

So what i do is, in the run method:

 if (status == 0xB0) // Control Change (CC)
    {
      const uint8_t ccNumber = event.data[1]; // Which CC (0-127)
      const uint8_t ccValue = event.data[2];  // CC value (0-127)
      float normalizedValue = ccValue / 127.0f;
      if (ccNumber == 82) {
        setParameterValue(static_cast<uint32_t>(MyPluginParameter::kParameterSomeParam), normalizedValue);

and then

mydsp->setSomeParams(someValue)

in the setParameterValue, i affect the MyPluginParameter::kParameterSomeParam value to someValue

So this works well.

But in the GUI, the parameterChanged method does not receive these parameter changes.

Note that in a plugin situation, when the host sends param changes, both UI and DSP react correctly to changes.

So how to handle this CC -> param change situation ?

Thanks !

[falkTX]

Best to set the default midiCC hint and let DPF handle that, which it does already.
See https://github.com/DISTRHO/DPF/blob/main/distrho/DistrhoDetails.hpp#L650-L656

Current implementation at https://github.com/DISTRHO/DPF/blob/main/distrho/src/DistrhoPluginJACK.cpp#L465-L488

PS: You can't just be changing your own parameters and expecting the host to know about it, there is an API for this https://github.com/DISTRHO/DPF/blob/main/distrho/DistrhoPlugin.hpp#L147-L163 but expect it to not be universal. It is more to be used if you have some control of the host side too.

[nniippsseell-source]

Thanks a lot for your answer.

Best to set the default midiCC hint and let DPF handle that, which it does already.

That's nice ! Is it possible to change this value dynamically (to let user assign its own controls by implementing a cc assign mode in ui and dsp) ? It seems to be the case as those are read directly in the jack_process callback, but just to be sure, can you confirm ?

Jack standalone use the DISTRHO_PLUGIN_WANT_PARAMETER_VALUE_CHANGE_REQUEST can/request value change, am i correct ?

This leads me to a slightly unrelated question: on the UI side, it is expected that the UI can SetParameterValue that will inform host and then propagate to the dsp, right ? And this will work with jack standalone host ? Or should i also use the value change request or another mechanism ?

Thanks.

[falkTX]

That's nice ! Is it possible to change this value dynamically (to let user assign its own controls by implementing a cc assign mode in ui and dsp) ? It seems to be the case as those are read directly in the jack_process callback, but just to be sure, can you confirm ?

no, parameters are created only once and then their data cannot change. potentially could change the name as that would be only a visual change and no host logic behind it, but there is no way to do this now anyway.

Jack standalone use the DISTRHO_PLUGIN_WANT_PARAMETER_VALUE_CHANGE_REQUEST can/request value change, am i correct ?

correct. implemented on a few plugin formats, but support will depend on the host. not all support this.

This leads me to a slightly unrelated qestion: on the UI side, it is expected that the UI can SetParameterValue that will inform host and then propagate to the dsp, right ? And this will work with jack standalone host ? Or should i also use the value change request or another mechanism ?

ui -> dsp parameter changes always work, there are no limitations for that.

[nniippsseell-source]

no, parameters are created only once and then their data cannot change.

Ah, ok, very good to know. So i guess i'll use hints first if jack standalone use them and find the correct way to do assignation later. I need cc assignation ONLY for standalone anyway (i certainly won't go the host automation fighting against CC route).but i want them for sure in this case.

ui -> dsp parameter changes always work, there are no limitations for that.

Ok, that's good !

Now, last question: I noticed that when inside a host (ardour in my case), i do setParameterValue in the GUI and receive a parameterChanged that allow me to update the GUI. But this is not the case in the jack standalone: the same setParameterValue do not cause the GUI to receive this parameterChanged. So i have to do an "optimistic" update of the gui (change the gui value hoping the change has been propagated correctly). Am i doing something wrong, is this the expected behavior from Ardour and jack standalone host ? (i use latest ardour & DPF)

Thanks !

[falkTX]

Now, last question: I noticed that when inside a host (ardour in my case), i do setParameterValue in the GUI and receive a parameterChanged that allow me to update the GUI. But this is not the case in the jack standalone: the same setParameterValue do not cause the GUI to receive this parameterChanged. So i have to do an "optimistic" update of the gui (change the gui value hoping the change has been propagated correctly). Am i doing something wrong, is this the expected behavior from Ardour and jack standalone host ? (i use latest ardour & DPF)

It is your responsibility to update the UI when some user action has triggered a parameter change.
So if a user moved a knob, the UI is already updated since that knob has moved, the only action needed is that setParameterValue to notify the host.

In this case Ardour seems to be giving back the param change to the UI yet again, which I would consider a bit non-standard. It can easily lead to feedback loops.
Don't assume hosts will behave like this, most won't give back your value change again, Ardour is the odd one here (and likely only for a few specific plugin formats too)

[nniippsseell-source]

Ok, noted!
A big thank you for your fast and excellent answers!