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