# Lesson 19

# Randomization Lesson. In this lesson,
# you will learn how to introduce an
# element of chance or randomization
# into your Sonic Pi code.

# General Instructions:
#
# This lesson contains two examples and
# three exercises (A, B, C).
#
# 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: Randomizing arrays.

comment do
  in_thread do
    loop do
      play chord(:C, :minor7).choose
      sleep 0.5
    end
  end
  in_thread do
    loop do
      play scale(:C, :minor_pentatonic).tick
      sleep 0.5
    end
  end
  melody = [:C5, :Eb5, :G5, :Ab5, :B4,
          :G5, :Gb5, :F5, :E5, :Eb5,
          :D4, :C5, :B4, :C5, :F5,
          :Eb5, :D5, :C5]
  loop do
    play melody.choose
    sleep 0.25
  end
end

# Exercise A:
# The choose command selects a random element
# from a ring or an array. Sonic Pi has
# built-in chord and scale arrays which work
# with the choose command. Change Example 1
# in the following ways:
#   1) Change the chord root and type in the
#      first thread.
#   2) Change to different kinds of scales in the
#     Sonic Pi system and change the tonic note.
#   3) Change the notes of the melody array.
#

# Example 2: Randomizing numbers
# There are several ways to randomize note
# selection in Sonic Pi using random numbers.
# The rrand command will select a random real
# number within a given range. This works well
# for selecting pitches directly. The rrand_i
# command selects whole numbers (integers),
# which is a good way to select an index
# into an array.

comment do
  in_thread do
    loop do
      play rrand(35.6, 120.9)
      sleep 0.25
    end
  end
  melody = [:C5, :Eb5, :G5, :Ab5, :B4,
          :G5, :Gb5, :F5, :E5, :Eb5,
          :D4, :C5, :B4, :C5, :F5,
          :Eb5, :D5, :C5]
  loop do
    index = rrand_i(0, melody.length - 1)
    play melody[index]
    sleep 0.5
  end
end

# Exercise B:
# Change Example 2 in the following ways:
#   1) Change the melody array to a ring, and
#      make the lower value of the range for the
#      index a negative number (< 0).
#   2) Restrict the range for notes in the
#      rrand statement in the first thread
#      to less than one whole number.
#   3) Experiment with random sleep times
#      for both threads.
#

# Exercise C:
# Create a loop that plays samples with
# changing rates. Use the rrand command to
# select the sample rate. Try using both
# negative and positive numbers for the
# sample rate.