Octavian is a little utility library for working with musical notes and their frequencies. Super cool, right?

First things, first: how do I install this thing?

npm install octavian

Maybe you even throw a --save in there if you feel like keeping it around.

So, we've got Octavian installed, how do we use it?

var Octavian = require('octavian');

var note = new Octavian.Note('A4');

Or, if you're some kind of hipster…

var Note = require('octavian').Note;

var note = new Note('A4');

A Note has a few properties that we can play around with.

var note = new Note('A#4');

note.letter; // 'A'
note.modifier; // '#'
note.octave; // 4
note.signature; // 'A#4'
note.pianoKey; // 50
note.frequency; // 466.164

But, what if we toss in some bogus note? Something like E#, maybe? There is no E#, right?

var note = new Note('E#5');

note.signature; // 'F5'

Music is all about intervals. We can move up by a semitone or some other interval.

var note = new Note('C3');

note.majorThird(); // returns a new Note('E3');
note.perfectFifth(); // returns a new Note('G3');
note.perfectOctave(); // returns a new Note('C4');

You can do any of the following:

• downOctave()
• minorSecond()
• majorSecond()
• minorThird()
• majorThird()
• perfectFourth()
• diminishedFifth()
• perfectFifth()
• minorSixth()
• majorSixth()
• minorSeventh()
• majorSeventh()
• perfectOctave()

There are also some extra methods that are aliased, if you'd prefer:

• augmentedFourth()
• third()
• fifth()

You can create chords with Octavian.

const cMajorChord = new Octavian.Chord('C4', 'major');

cMajorChord.notes; // returns [ { letter: 'C', modifier: null, octave: 4 },
                   //           { letter: 'E', modifier: null, octave: 4 },
                   //           { letter: 'G', modifier: null, octave: 4 } ]

cMajorChord.signatures;  // returns [ 'C4', 'E4', 'G4' ]
cMajorChord.frequencies; // returns [ 261.626, 329.628, 391.995 ]
cMajorChord.pianoKeys;   // returns [ 40, 44, 47 ]

You can create the following chords:

• major
• majorSixth
• majorSeventh
• majorSeventhFlatFive
• majorSeventhSharpFive
• minor
• minorSixth
• minorSeventh
• minorMajor
• dominantSeventh
• diminished
• diminishedSeventh
• halfDimished

You're also more than welcome to use the following aliases for any of the above:

• maj is an alias for major
• 6 is an alias for majorSixth
• maj6 is an alias for majorSixth
• 7 is an alias for majorSeventh
• maj7 is an alias for majorSeventh
• maj7b5 is an alias for majorSeventhFlatFive
• maj7#5 is an alias for majorSeventhSharpFive
• min is an alias for minor
• m is an alias for minor
• min6 is an alias for minorSixth
• m6 is an alias for minorSixth
• min7 is an alias for minorSeventh
• m7 is an alias for minorSeventh
• m#7 is an alias for minorMajor
• min#7 is an alias for minorMajor
• m(maj7) is an alias for minorMajor
• dom7 is an alias for dominantSeventh
• dim is an alias for diminished
• dim7 is an alias for diminishedSeventh
• m7b5 is an alias for halfDiminshed

You can add notes to a chord manually, if that suits you:

const chord = new Octavian.Chord('C4');

chord.signatures; // returns ['C4']

chord.addInterval('majorThird');
chord.signatures; // returns ['C4', 'E4']

chord.addInterval(7);
chord.signatures; // returns ['C4', 'E4', 'G4']

You can turn any note into the basis for a chord:

const note = new Octavian.Note('C4');
note.toChord(); // returns a new chord with only C4 in it.
note.toChord('major'); // returns a new chord with C4, E4, and G4 in it

You can invert a chord. For a Triad, two inversions exist these can be created by calling inversion(1) or inversion(2).

const cMajorChord = new Octavian.Chord('C4', 'major');
cMajorChord.signatures;  // returns [ 'C4', 'E4', 'G4' ]

cMajorChord.inversion(2);
cMajorChord.signatures;  // returns [ 'C5', 'E5', 'G4' ]

It's also possible to have Octavian generate a random inversion:

const cMajorChord = new Octavian.Chord('C4', 'major');
cMajorChord.randomInversion();
cMajorChord.signatures;  // returns any one of the following:
                         // [ 'C4', 'E3', 'G3' ]
                         // [ 'C4', 'E4', 'G3' ]
                         // [ 'C4', 'E4', 'G4' ]
                         // [ 'C5', 'E4', 'G4' ]
                         // [ 'C5', 'E5', 'G4' ]