Polyrhythm Trainer (#194)

Ruby
1

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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 recently had an article about
graphical toolkits if you are interested.

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

Have Fun!

2

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

3

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