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+### Remarks
+
+Run the program under a platform that `/dev/dsp` is available.
+For example, if you are using pulseaudio, use `padsp`:
+
+    padsp ruby entry.rb
+
+Please see Limitation if you want to run this program on os x.
+
+I confirmed the following platforms.
+
+* ruby 2.0.0p0 (2013-02-24 revision 39474) [x86\_64-linux]
+* ruby 1.9.3p194 (2012-04-20 revision 35410) [x86\_64-linux]
+* ruby 1.9.3p327 (2012-11-10 revision 37606) [x86\_64-darwin10.8.0]
+
+For those who are lazy, I'm attaching a screencast.
+
+### Description
+
+This program is a music-box quine.
+It prints itself with playing "Jesu, Joy of Man's Desiring".
+
+### Internal
+
+Like a real music box, this program consists of a mechanical part (code) and a piano roll.
+In the piano roll, `#` represents a pin that hits a note, and `|` represents a slur.
+The leftmost column corresponds 110Hz (low A).
+Every column corresponds a semitone higher than the left one.
+
+This program uses [the frequency modulation synthesis](http://en.wikipedia.org/wiki/Frequency_modulation_synthesis) to play the sound like a music-box.
+You can create a different-sounding tone by changing the parameter.
+For example, the following will play the sound like a harpsichord.
+
+    padsp ruby entry.rb 2.0
+
+Note that this program does *not* use an idiom to remove whitespace, such as `.split.join`.  All newlines and spaces do not violate any of the Ruby syntax rules.
+
+### Limitation
+
+On os x, `/dev/dsp` is not available.
+You have to use sox by replacing the following part:
+
+    open("/dev/dsp","wb")
+
+with:
+
+    IO.popen("./pl","wb")
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