Musical Instrument Digital Interface (MIDI) can be found at http://www.midi.org. It is an international standard that enables various electronic musical instruments to communicate with each other. Pure Data has an extensive support of the MIDI operations. In this section, we look into simple use of MIDI signals in audio programming. We do not, however, assume readers will have external MIDI devices to work on with our examples. There are virtual synthesizers in various platforms where Pure Data is supported. We are going to use the virtual synthesizers to generate sound, instead of using external MIDI hardware. For the inputs, we'll just use the Pure Data number boxes to create the notes, instead of using a MIDI keyboard.
For Windows, built-in Microsoft GS Wavetable Synth can handle the MIDI output. For Linux, we can install TiMidity++ through your package manager or from http://timidity.sourceforge.net. For Mac OSX, we need to install the SimpleSynth software tool from...