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SequencerPi

This library, at the highest level, consists of an interface between a MIDI synthesizer and a web browser using a RaspberryPi as the middleware that serves both MIDI messages to the synthesizer and HTTP messages to the browser. It allows the user to create, play, edit and loop a sequence of notes using a button matrix.

Layers

SequencerPi consists of 3 main layers:

  1. JavaScript user interface: Displays the interactive panel in a simple HTML file and sends HTTP requests through socket.io to the nodejs server notifying any note addition, removal or playback changes.
  2. Nodejs server: Connects to the JS interface using a simple HTTP server and socket.io and to the MIDI library using a custom node C++ module.
  3. C++ ALSA MIDI library: Handles all the sequencing, queueing and messaging logic between the Linux ALSA and the MIDI device connected to the Raspberry Pi.

sequencerpi diagram

Requirements

This library can be compiled in a RaspberryPi running a Linux distribution like xbian or raspbian. The required packages for compilation are:

  • node
  • node-gyp (install with npm)
  • socket.io (install with npm)
  • libasound2-dev

To build the node module, use the following command in the node/ directory.

node-gyp configure build

This will generate the required libraries to run the nodejs server.

Usage

To test, connect a MIDI synthesizer device (USB or using a USB MIDI interface) to a RaspberryPi and run the nodejs server.

node midi.js

After this, navigate to http://localhost:8080, write a sequence using the button controls and hit Play. Events will be fired to the MIDI device.