The piano plays sound

elements/fun/music/music.go

@@ -0,0 +1,69 @@
+package music
+
+import "math"
+
+var semitone = math.Pow(2, 1.0 / 12.0)
+
+// Tuning is an interface representing a tuning.
+type Tuning interface {
+	// Tune returns the frequency of a given note in Hz.
+	Tune (Note) float64
+}
+
+// EqualTemparment implements twelve-tone equal temparment.
+type EqualTemparment struct { A4 float64 }
+
+// Tune returns the EqualTemparment frequency of a given note in Hz.
+func (tuning EqualTemparment) Tune (note Note) float64 {
+	return tuning.A4 * math.Pow(semitone, float64(note - NoteA4))
+}
+
+// Octave represents a MIDI octave.
+type Octave int
+
+// Note returns the note at the specified scale degree in the chromatic scale.
+func (octave Octave) Note (degree int) Note {
+	return Note(int(octave + 1) * 12 + degree)
+}
+
+// Note represents a MIDI note.
+type Note int
+
+const (
+	NoteC0 Note = iota
+	NoteDb0
+	NoteD0
+	NoteEb0
+	NoteE0
+	NoteF0
+	NoteGb0
+	NoteG0
+	NoteAb0
+	NoteA0
+	NoteBb0
+	NoteB0
+
+	NoteA4 Note = 69
+)
+
+// Octave returns the octave of the note
+func (note Note) Octave () int {
+	return int(note / 12 - 1)
+}
+
+// Degree returns the scale degree of the note in the chromatic scale.
+func (note Note) Degree () int {
+	mod := note % 12
+	if mod < 0 { mod += 12 }
+	return int(mod)
+}
+
+// IsSharp returns whether or not the note is a sharp.
+func (note Note) IsSharp () bool {
+	degree := note.Degree()
+	return degree == 1 ||
+		degree == 3 ||
+		degree == 6 ||
+		degree == 8 ||
+		degree == 10
+}