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+++ b/music.rst	Thu Feb 18 21:08:35 2016 +0200
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+.. -*- coding: utf-8; -*-
+.. include:: HEADER.rst
+
+========
+ Music.
+========
+.. contents::
+
+Music scale.
+============
+
+*Scale* is any set of musical notes ordered by fundamental frequency or pitch.
+
+Scale ordered by increasing pitch is an *ascending scale*, and a scale ordered
+by decreasing pitch is a *descending scale*.
+
+The distance between two successive notes in a scale is called a *scale step*.
+
+For Western music with 12 tones in octave used several definition of steps:
+
+ * *semitone*, *half step* is 2^(1/12)
+ * *whole step*, *whole tone*, *major second* is 2^(2/12)
+
+*Chromatic scale* is a musical scale with twelve pitches, each a semitone
+above or below another. On a modern piano or other equal-tempered
+instrument, all the semitones have the same size (100 cents). In other
+words, the notes of an equal-tempered chromatic scale are equally spaced.
+
+ * https://en.wikipedia.org/wiki/Chromatic_scale
+
+*Diatonic scale* (or heptatonia prima) is a scale composed of seven distinct
+pitch classes: ``2–2–1–2–2–2–1``.
+
+ * https://en.wikipedia.org/wiki/Diatonic_scale
+
+*Minor scale*: ``2-1-2-2-1-2-2``.
+
+ * https://en.wikipedia.org/wiki/Minor_scale
+
+Pentatonic major scale: ``1, 2, 3, 5, 6``.
+Pentatonic minor scale: ``1, ♭3, 4, 5, ♭7``.
+
+ * https://en.wikipedia.org/wiki/Pentatonic_scale
+
+The eight degrees of the diatonic scale are also known by traditional names:
+
+ * 1st degree – Tonic (key note)
+ * 2nd degree – Supertonic
+ * 3rd degree – Mediant
+ * 4th degree – Subdominant
+ * 5th degree – Dominant
+ * 6th degree – Submediant
+ * 7th degree – Leading tone
+ * 8th degree – Tonic (Octave)
+
+Intervals names:
+
+* *Minor second* - 1 semitones.
+* *Major second* - 2 semitones.
+* *Minor third* - 3 semitones.
+* *Major third* - 4 semitones.
+* *Perfect fourth* - 5 semitones, 4:3.
+* *Perfect fifth* - 7 semitones, 3:2.
+* *Minor sixth* - 8 semitones.
+* *Major sixth* - 9 semitones.
+* *Minor seventh* - 10 semitones.
+* *Major seventh* - 11 semitones.
+
+The notes of a scale are numbered by their steps from the root of the scale.
+
+  https://en.wikipedia.org/wiki/Scale_%28music%29
+    Often, especially in the context of the common practice period, most or all
+    of the melody and harmony of a musical work is built using the notes of a
+    single scale, which can be conveniently represented on a staff with a
+    standard key signature.
+  https://en.wikipedia.org/wiki/Common_practice_period
+    Common-practice harmony is almost always derived from diatonic scales and
+    tends to follow particular chord progressions that have withstood the test
+    of time.
+