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

Polyrhythm is the simultaneous sounding of two or more independent

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

  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

  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
    @time += time_elapsed
    @last_hit += time_elapsed
    return hit

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

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
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


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).