# Lesson 18

# Chord Progressions Lesson. In this lesson,
# you will create various chord progressions
# using various techniques from previous lessons.

# General Instructions:
#
# This lesson contains one example and
# one exercise (A).
#
# To listen to an example, change "comment"
# to "uncomment" on the "comment do" line,
# then click the "Run" menu command at the
# top of the Sonic Pi editor window.
# When you are done with the example, turn
# it off by changing "uncomment" back to
# "comment," and move on to the next section
# of the lesson.
#

# Example 1: Primary Triads.

comment do
  define :primary do | key, major |
    roots = [key, key + 5, key + 7]
    if major == true
      third = 4
    else
      third = 3
    end
    index = 0
    3.times do
      play roots[index]
      sleep 0.5
      play roots[index] + third
      sleep 0.5
      play roots[index] + 7
      sleep 0.5
      play roots[index] + third
      sleep 0.5
      play roots[index]
      sleep 0.5
      play roots[index]
      play roots[index] + third
      play roots[index] + 7
      sleep 1
      index += 1
    end
  end

  primary :C4, true
  sleep 1
  primary :D4, false
  sleep 1
  primary :G4, true
end

# Exercise A:
# Change Example 1 in the following ways:
#   1) Change the code so that the third
#      chord in the progression (V) is always
#      major, even when the key is minor; that
#      is, create a i - iv - V progression
#      as in harmonic minor.
#   2) Change the code so that a bass note
#      plays the root of each chord and
#      three upper notes play the chord in
#      close position: I - IV6/4 - V6/5 - I.
#      For example, if you send :C4 as an
#      argument for the key parameter, you
#      hear :C4 :F4 :G4 :C4 in the bass, and
#      :C5+:E5+:G5, :C5+:F5+:A5, :B4+:F5+:G5,
$      :C5+:E5+:G5 in the upper voices.