Skip to content

Latest commit

 

History

History
108 lines (74 loc) · 4.1 KB

simplesaw-plugin.rst

File metadata and controls

108 lines (74 loc) · 4.1 KB

LV2 Audio-Plugin Workshop OSAMC

Author: Christopher Arndt
Date: 2018-08-11

Let's create a plug-in, which generates some audio output itself. It will output a sawtooth wave, whose frequency can be controlled via a plug-in parameter. We'll call the plug-in "SimpleSaw".

We can simply generate the same project as for the SimpleGain plug-in and then change the source code in a few places to make the plug-in do something different. You can see all the changes in detail in this commit in the GitHub repository for the plug-in.

Simple Saw Plugin

  1. Initialize a new DSP audio plug-in project with cookiecutter and name it SimpleSaw.

  2. Copy the following files from this repository into the plugins/SimpleSaw directory:

    • WaveTableOsc.{c,h}pp
    • WaveUtils.{c,h}pp

    If you download the files via the GitHub web interface, make sure you get the actual raw files, not the HTML pages displaying the source code of the files (use the "Raw" button on the source disply page of each file).

  3. Add these objects to the OBJ_DSP list in the Makefile in plugins/SimpleSaw before PluginSimpleSaw.cpp.o (don't forget the backslashes to keep the whole assignment on one logical line):

    WaveTableOsc.cpp.o \
WaveUtils.cpp.o \

  4. Add #include "WaveUtils.hpp" to plugins/SimpleSaw/PluginSimpleSaw.hpp after the #include that's already in there.

  5. Add WaveTableOsc *osc; to the private Section of the PluginSimpleSaw class in plugins/SimpleSaw/PluginSimpleSaw.hpp and remove the double fSampleRate; line there.

  6. Add osc = sawOsc(); in the constructor method of the PluginSimpleSaw class in plugins/SimpleSaw/PluginSimpleSaw.cpp before the loadProgram(0); line and remove the sampleRateChanged(getSampleRate()); line.

  7. Change every occurence of paramVolume to paramFrequency in plugins/SimpleSaw/PluginSimpleSaw.hpp and plugins/SimpleSaw/PluginSimpleSaw.cpp.

  8. Change the initParameter method of the PluginSimpleSaw class to set the name and symbol of the parameter to "Frequency" resp. "frequency" and its min/max/default values to 20.0 / 10000.0 and 440.0;

  9. Change the for loop in the run method of the PluginSimpleSaw class to the following:

    // output the oscillator waveform
for (uint32_t i=0; i < frames; ++i) {
    outL[i] = osc->getOutput() * 0.8;
    outR[i] = osc->getOutput() * 0.8;
    osc->updatePhase();
}

    and remove the lines initializing the inpL, inpR and vol variables.

    Optionally, remove the input name from the method parameters, since the plug-in doesn't use the audio inputs.

  10. Change the body of the setParametervalue method of the PluginSimpleSaw class to the following:

    fParams[index] = value;

switch (index) {
    case paramFrequency:
        osc->setFrequency(value / getSampleRate());
        break;
}

  11. Change the body of the loadProgram method of the PluginSimpleSaw class to the following:

    switch (index) {
    case 0:
        setParameterValue(paramFrequency, 440.0f);
        break;
}

    (Only the second parameter in the call to setParameterValue changes.)

  12. Change the body of the sampleRateChanged method of the PluginSimpleSaw` class to the following single line:

    osc->setFrequency(fParams[paramFrequency] / newSampleRate);

  13. Set the value of the DISTRHO_PLUGIN_NUM_INPUTS pre-processor definition in DistrhoPluginInfo.h to 0.

  14. Compile the plug-in, copy or symlink the LV2 plug-in to ~/.lv2 and test it with jalv or another LV2 host of your liking.