Code made for https://youtu.be/xboQRfXnpZ0

furelise.rb

require 'muse'
include Muse

def intro(num)
  bar(num + 1, b:0.25).notes { e5; dis5; }

  bar(num + 2, b:0.25).notes { e5; dis5; e5; b4; d5; c5; }

  bar(num + 3, b:0.25).notes { a4 b:0.5; _; c4; e4; a4; }
  bar(num + 3, b:0.25).notes { a2; e3; a3; _ b:0.75 }

  bar(num + 4, b:0.25).notes { b4 b:0.5; _; e4; gis4; b4; }
  bar(num + 4, b:0.25).notes { e2; e3; gis3; _ b:0.75 }

  bar(num + 5, b:0.25).notes { c5 b:0.5; _; e4; e5; dis5; }
  bar(num + 5, b:0.25).notes { a2; e3; a3; _ b:0.75 }

  bar(num + 6, b:0.25).notes { e5; dis5; e5; b4; d5; c5; }

  bar(num + 7, b:0.25).notes { a4 b:0.5; _; c4; e4; a4; }
  bar(num + 7, b:0.25).notes { a2; e3; a3; _ b:0.75 }

  bar(num + 8, b:0.25).notes { b4 b:0.5; _; e4; c5; b4; }
  bar(num + 8, b:0.25).notes { e2; e3; gis3; _ b:0.75 }

  bar(num + 9, b:0.25).notes { a4 b:0.5; _ b:1;  }
  bar(num + 9, b:0.25).notes { a2; e3; a3; _ b:0.75 }
end

Song.record "fur_elise", bpm: 60 do
  intro 0
  intro 9

  bar(18, b:0.25).notes { _ b:0.75; b4; c5; d5; }
  bar(18, b:0.25).notes { _ b:1.5; }

  bar(19, b:0.25).notes { e5 b:0.75; g4; f5; e5; }
  bar(19, b:0.25).notes { c3; g3; c4; _ b:0.75 }

  bar(20, b:0.25).notes { d5 b:0.75; f4; e5; d5; }
  bar(20, b:0.25).notes { g2; g3; b3; _ b:0.75 }

  bar(21, b:0.25).notes { c5 b:0.75; e4; d5; c5; }
  bar(21, b:0.25).notes { a2; e3; a3; _ b:0.75 }

  bar(22, b:0.25).notes { b4 b:0.5; _; e4; e5; _ }
  bar(22, b:0.25).notes { e2; e3; e4; _; _; e4 }

  bar(23, b:0.25).notes { _; e5; e6; _; _; dis5; }
  bar(23, b:0.25).notes { e5; _; _; dis5; e5; _; }


end

harmonic.rb

# Muse
# Copyright (C) 2012  Chang Sau Sheong
# 
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# 
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
# 
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

module Muse
  module Harmonic
    class << self
      
      def base(input)
        2 * Math::PI * input
      end
      
      def default(input)
        Math.sin(base(input))
      end

      def second(input)
        Math.sin(base(input))
        Math.sin(base(input) * 3)
      end

      def third(input)
        Math.sin(base(input)) + 
        Math.sin(base(input) * 3) + 
        Math.sin(base(input) * 5)
      end

      def guitar(input)
        Math.sin(base(input)) + 
        Math.sin(base(input) * 2) + 
        Math.sin(base(input) * 0.5)
      end

      def piano(input)
        ret = Math.sin(base(input)) * Math.exp(-0.004 * base(input))
        ret += Math.sin(2 * base(input)) * Math.exp(-0.0004 * base(input)) / 2
        ret += Math.sin(3 * base(input)) * Math.exp(-0.0004 * base(input)) / 4
        ret += Math.sin(4 * base(input)) * Math.exp(-0.0004 * base(input)) / 8
        ret += Math.sin(5 * base(input)) * Math.exp(-0.0004 * base(input)) / 16
        ret += Math.sin(6 * base(input)) * Math.exp(-0.0004 * base(input)) / 32

        ret += ret * ret * ret
      end

    end
  end
end