Forum: Ruby Polyrhythm Trainer (#194)

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## Polyrhythm Trainer (#194)

Greetings fellow Rubyists,

This week's quiz is to create a polyrhythm training program. The user
will be prompted to tap out a rhythm with two keys: left and right.
Each time the user presses a key the program will display how close to
the correct timing the key press occurred. The program will be
configurable to train the user in any polyrhythm 2:3, 5:4, 11:17, and
so on. The program will also have a configurable tempo. After a number
of complete rhythms the program will display the ratio of how many
notes were successfully struck, success determined by being within a
threshold around the perfect timing.

The display can be as simple as a console application or use a full
graphical interface. [Ruby Inside][1] recently had an article about
graphical toolkits if you are interested.

[Polyrhythm][2] is the simultaneous sounding of two or more independent 
rhythms.

[1]: 
http://www.rubyinside.com/ruby-gui-programming-survey-results-1552.html
[2]: http://en.wikipedia.org/wiki/Polyrhythm

Have Fun!

This quiz may be worthy of a revisit in the future. Until then, here
is my solution: the beginnings of an "Annoyance" trainer.

    # rhythm.rb

    class Rhythm
      BPM = 20
      SECONDS_PER_MINUTE = 60.0

      def initialize(n, sym)
        @sym = sym
        @seconds_per_hit = SECONDS_PER_MINUTE/(BPM*n)
        @last_hit = @seconds_per_hit
        @hit_count = 0
        @time = 0

        puts @seconds_per_hit
      end

      def elapse(time_elapsed)
        hit = false
        if @last_hit >= @seconds_per_hit
          @hit_count += 1
          @last_hit -= @seconds_per_hit
          puts "#{"%1.3f" % @time}: #{@sym}"
          hit = true
        end
        @time += time_elapsed
        @last_hit += time_elapsed
        return hit
      end
    end

    s = '@'

    rhythms = ARGV.map{|arg| Rhythm.new(arg.to_i, s = s.succ)}

    delta = 0.05
    time = 0

    while true
      hit = rhythms.map{|r| r.elapse(delta)}.inject(false) {|hit, r| hit 
|| r}
      print "\a" if hit
      time += delta
      sleep delta
    end

The program will beep indefinitely, producing a sound every time the
rhythm should be struck (to the nearest 20th of a second).

    Usage: ruby rhythm.rb [rhythms]

    EX: > ruby rhythm.rb 3 2
    1.0
    1.5
    0.000: A
    0.000: B
    1.000: A
    1.500: B
    2.000: A
    3.000: A
    3.000: B
    4.000: A
    4.500: B
    5.000: A

Crank up the volume on your PC speaker and have a blast near your 
co-workers!

http://rubyquiz.strd6.com/quizzes/194

> configurable to train the user in any polyrhythm 2:3, 5:4, 11:17

11:17 is simply a modified 2:3, but I challenge anyone to do it with
any degree of precision at high tempo and only 2 references (2 keys).
If you can use your whole hand (as in playing a piano), it might be
easier.  Scriabin, for example, would frequently throw his poor
pianist into 11:3, 9:4, etc. brief, but frequent, frenzies (see piano
sonata no. 1 in F minor).

Todd