# Polyrhythm Trainer (#194)

**URL:** <https://www.ruby-forum.com/t/polyrhythm-trainer-194/161597>\
**Category:** Ruby\
**Created:** [February 27, 2009, 6:33pm UTC](https://www.ruby-forum.com/t/polyrhythm-trainer-194/161597 "2009-02-27T18:33:10Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![danmcb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/13edae/32.png) [@danmcb](https://www.ruby-forum.com/u/danmcb)\
**Post date:** [February 27, 2009, 6:33pm UTC](https://www.ruby-forum.com/t/polyrhythm-trainer-194/161597/1 "2009-02-27T18:33:10Z")

</div>

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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](http://www.rubyinside.com/ruby-gui-programming-survey-results-1552.html) recently had an article about  
graphical toolkits if you are interested.

[Polyrhythm](http://en.wikipedia.org/wiki/Polyrhythm) is the simultaneous sounding of two or more independent  
rhythms.

Have Fun!

---

<div class="post-metadata">

**Author:** ![danmcb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/13edae/32.png) [@danmcb](https://www.ruby-forum.com/u/danmcb)\
**Post date:** [March 7, 2009, 8:55pm UTC](https://www.ruby-forum.com/t/polyrhythm-trainer-194/161597/2 "2009-03-07T20:55:19Z")

</div>

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](http://rubyquiz.strd6.com/quizzes/194)

---

<div class="post-metadata">

**Author:** ![danmcb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/13edae/32.png) [@danmcb](https://www.ruby-forum.com/u/danmcb)\
**Post date:** [March 8, 2009, 10:52pm UTC](https://www.ruby-forum.com/t/polyrhythm-trainer-194/161597/3 "2009-03-08T22:52:31Z")

</div>

> 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