MIDI control connection for Sonic Pi

drb_server.rb

#!/usr/bin/env ruby
# encoding: utf-8

require 'drb/drb'
require 'micromidi'

# The URI we're using for RDb, we use unix sockets just because they're quicker.
DRB_URI="drbunix:/var/tmp/sonic-pi-midiconnector"

class SPIMidiConnector

  def initialize
    @input = UniMIDI::Input.use(0)
    @midithread = listen()
  end

  # Return the value of the pot.
  #
  # If we haven't moved a pot yet then just return 0.
  def get(key)
    @midithread[key] || 0
  end

  # Some convenience methods (they're shorter to type while livecoding).
  # These should return the midi value (0 to 127) of the potentiometer on the LPD8.
  def k1; get(:k1); end
  def k2; get(:k2); end
  def k3; get(:k3); end
  def k4; get(:k4); end
  def k5; get(:k5); end
  def k6; get(:k6); end
  def k7; get(:k7); end
  def k8; get(:k8); end
 
  def thread
    @midithread
  end

private

  def listen
    midithread = Thread.new(@pads_map) do |pad_map|
      MIDI.using(@input) do

        # When we get a control change message, update a
        # thread attribute with the value.
        thru_except :control_change do |msg|
          key = "k#{msg.data[0]}".to_sym
          puts "key: #{key} value: #{msg.value}"
          midithread[key] = msg.value
        end

        join
      end
    end
    midithread
  end
end

# Then we start the DRb server, as per the DRb docs.

FRONT_OBJECT = SPIMidiConnector.new

$SAFE = 1

DRb.start_service(DRB_URI, FRONT_OBJECT)
DRb.thread.join

sonic_pi_client.rb

require 'drb/drb'
DRB_URI="drbunix:/var/tmp/sonic-pi-midiconnector"
@lpd = DRbObject.new_with_uri(DRB_URI)

use_bpm 120

live_loop :kick do
  sample :bd_haus
  sleep 1
end

with_fx :bitcrusher do
  live_loop :saw do
    sync :kick
    use_synth :dsaw
    play chord(:c, :major, num_octaves: 4).choose,  cutoff: @lpd.k1, release: 2, attack: 1
    sleep 0.5
  end
end

The aim of all this is to try and use the LPD8 with Sonic Pi. I want to keep track of the eight pots on the right hand side (labelled up as K1 to K8).

Currently using dRuby because it's part of the Ruby std-lib and I didn't want to mess with Sonic Pi too much. You could start caching on the client side too, but it doesn't seem to need it yet.

The Sonic Pi example just lets you change the cutoff by turning the K1 pot.