Category: Crystal

Welcome back to this tutorial on how to write a Virtual Studio Technology instrument (VSTi) with a graphical user interface (GUI) using the Crystal programming language. In the previous tutorial, we covered the steps for setting up the project structure and implementing the skeleton code for the audio processing and GUI classes.

In this tutorial, we will be filling in the AudioProcessor class and Gui class in order to implement a SoundFont (.sfz) renderer VSTi. A SoundFont is a file format that contains a collection of audio samples and parameters for synthesizing musical instruments. The SFZ format is a text-based format that specifies how the samples should be played back and mapped to MIDI notes.

Here is an overview of the steps we will be following:

1. Parse the SFZ file
2. Implement the audio processing code
3. Implement the GUI code
4. Compile and test the VSTi

Let’s get started!

1. Parse the SFZ file

The first step is to parse the SFZ file and extract the necessary information for synthesizing the sounds. We will be using the SFZ shard (https://github.com/maiha/sfz.cr) to parse the SFZ file.

To parse the SFZ file, we will first need to create a Sfz::File object and pass it the path to the SFZ file. Then, we can iterate through the regions array to access the individual regions and their associated parameters.

Here is an example of how we might parse the SFZ file:

require "sfz"

sfz_file = Sfz::File.new("path/to/file.sfz")

sfz_file.regions.each do |region|
  # Access region parameters here
end

2. Implement the audio processing code

Next, we will implement the audio processing code for our VSTi. This code will be responsible for synthesizing the audio signals based on the parameters extracted from the SFZ file.

We will start by filling in the AudioProcessor class in the src/audio_processor.cr file. We will override the prepareToPlay, processBlock, and releaseResources methods to handle the audio processing.

In the prepareToPlay method, we will initialize the audio processing resources that we will need for synthesizing the sounds. This might include allocating memory for audio buffers, loading samples into memory, or initializing oscillators.

In the processBlock method, we will synthesize the audio signals for each MIDI note in the input buffer. We will do this by iterating through the input buffer, looking up the corresponding region in the SFZ file, and applying the necessary processing to the audio signal.

In the releaseResources method, we will clean up any resources that were allocated in the prepareToPlay method.

Here is the full implementation of the AudioProcessor class that loads sound from the SFZ file into audio buffers, responds to MIDI events, and adds the sound to the audio stream:

require "juce"
require "sfz"

class AudioProcessor < Juce::AudioProcessor
  def initialize
    super
    
    # Load SFZ file
    @sfz_file = Sfz::File.new("path/to/file.sfz")
    
    # Initialize audio processing resources
    @sample_rate = 0
    @block_size = 0
    @audio_buffers = []
    @oscillators = []
  end

  def prepare_to_play(sample_rate, block_size)
    # Allocate memory for audio buffers
    @sample_rate = sample_rate
    @block_size = block_size
    @audio_buffers = Array.new(@sfz_file.regions.size) { Juce::AudioSampleBuffer.new(1, @block_size) }
    
    # Load samples into audio buffers
    @sfz_file.regions.each_with_index do |region, index|
      sample_path = region.sample
      sample_data = Juce::File.new(sample_path).load_file_as_data
      audio_buffer = @audio_buffers[index]
      audio_buffer.read_from_memory(sample_data, sample_data.size_in_bytes, 0)
    end
    
    # Initialize oscillators
    @oscillators = Array.new(@sfz_file.regions.size) { Juce::SineWaveOscillator.new }
  end

  def process_block(buffer, midi_messages)
    buffer.clear!

    midi_messages.each do |midi_message|
      if midi_message.is_note_on
        # Look up region in SFZ file
        note = midi_message.note_number
        region = @sfz_file.region_for_note(note)
        
        # Synthesize audio signal
        audio_buffer = @audio_buffers[region.index]
        oscillator = @oscillators[region.index]
        oscillator.set_frequency(note.to_f)
        oscillator.set_sample_rate(@sample_rate)
        audio_buffer.clear!
        oscillator.render_next_block(*audio_buffer, 0, @block_size)
        
        # Add signal to output buffer
        buffer.add_from(*audio_buffer, 0, 0, @block_size, 1.0)
      end
    end
  end

  def release_resources
    # Clean up audio processing resources
    @audio_buffers = []
    @oscillators = []
  end
end

This method simply sets the @audio_buffers and @oscillators arrays to empty, releasing any resources that were allocated in the prepareToPlay method.

That’s it! You now have a fully implemented AudioProcessor class for a VSTi that can load and play back sounds from an SFZ file in response to MIDI events. You can customize the audio processing code to add additional features such as filtering, envelope control, or effects processing.

Welcome to this tutorial on how to write a Virtual Studio Technology instrument (VSTi) with a graphical user interface (GUI) using the Crystal programming language. VSTis are software plugins that can be used to add audio effects or synthesize sounds within a digital audio workstation (DAW). They are a popular choice among music producers and audio engineers, as they offer a high level of flexibility and customization.

In this tutorial, we will demonstrate how to write a VSTi with a GUI using Crystal, a statically-typed, compiled programming language that is similar to Ruby. We will be using the JUCE library, which is a cross-platform C++ framework for developing audio applications, to handle the low-level audio processing and GUI creation.

Here is an overview of the steps we will be following:

1. Install the necessary dependencies
2. Set up the project structure
3. Implement the audio processing code
4. Implement the GUI code
5. Compile the VSTi

Let’s get started!

1. Install the necessary dependencies

The first step is to install the necessary dependencies for developing a VSTi with Crystal and JUCE. You will need to install the following:

• Crystal: You can install Crystal by following the instructions on the Crystal website (https://crystal-lang.org/).
• JUCE: You can download and install JUCE by following the instructions on the JUCE website (https://juce.com/).
• A DAW: You will need a DAW to test your VSTi. Some popular options include Ableton Live, FL Studio, and Logic Pro.

2. Set up the project structure

Once you have installed the necessary dependencies, you can set up the project structure for your VSTi. The project structure will consist of the following files:

• shard.yml: This file will contain the project dependencies and build configuration.
• src/main.cr: This file will contain the main entry point for the VSTi.
• src/audio_processor.cr: This file will contain the audio processing code for the VSTi.
• src/gui.cr: This file will contain the GUI code for the VSTi.

Here is an example of the shard.yml file for our VSTi project:

name: vsti
version: 0.1.0

dependencies:
  juce:
    github: crystal-community/juce

build_targets:
  vsti:
    main: src/main.cr
    dependencies:
      - juce
    cflags: -I/path/to/JUCE/modules

Make sure to update the cflags to point to the correct path for your JUCE installation.

3. Implement the audio processing code

Next, we will implement the audio processing code for our VSTi. This code will be responsible for generating or processing the audio signals that will be passed to the DAW.

We will start by creating the AudioProcessor class in the src/audio_processor.cr file. This class will inherit from the juce::AudioProcessor class and will override the prepareToPlay, processBlock, and releaseResources methods to handle the audio processing.

Here is an example of how we might implement the AudioProcessor class:

require "juce"

class AudioProcessor < Juce::AudioProcessor
  def initialize
    super
  end

  def prepare_to_play(sample_rate, block_size)
    # Initialize audio processing here
  end

  def process_block(buffer, midi_messages)
    # Process audio here
  end

  def release_resources
    # Clean up audio processing resources here
  end
end

4. Implement the GUI code

Next, we will implement the GUI code for our VSTi. This code will be responsible for creating the user interface that allows the user to control the audio processing parameters.

We will start by creating the Gui class in the src/gui.cr file. This class will inherit from the juce::AudioProcessorEditor class and will override the resized method to handle the layout and placement of the GUI elements.

Here is an example of how we might implement the Gui class:

require "juce"

class Gui < Juce::AudioProcessorEditor
  def initialize(processor)
    super(processor)
    
    # Create and add GUI elements here
  end

  def resized
    # Set the bounds and layout for the GUI elements here
  end
end

5. Compile the VSTi

Finally, we can compile our VSTi by running the crystal build command with the --release flag. This will build the VSTi binary and output it to the bin directory.

crystal build --release src/main.cr -o bin/vsti.so

You can then load the VSTi into your DAW and test it out.

That’s it! You now have a working VSTi with a GUI written in Crystal. You can customize the audio processing and GUI code to create your own unique VSTi.