This software is in the alpha stage of development and is subject to change!

Goal

This library provides a way to identify chord names, and the associated root note, given a sequence of MIDI notes or note intervals. The current implementation can identify all 2- and 3-note permutations along with some popular chords.

If you have a MIDI keyboard attached to your computer, you can interact with a demo of this library at https://cmpadden.github.io/playground/chords

Usage

import { identify } from "chords.ts";

// Identify a sequence of MIDI notes
identify([48, 52, 55]).name;
// => 'C Major'

// Identify a sequence note letters
identify(["E", "F# / Gb", "A"]).name;
// => 'F# / Gb Minor 7'

How It Works

Note intervals are determined relative to the lowest note being played. For example, the notes E, G#, and B have the note interval 0, 4, 7. This interval is used to find the associated chord name in a lookup table. In this case, the interval maps to a Major chord, with a root note at 0, identified as the chord E Major. To reduce the number of possible note-permutations, duplicates are removed in other octaves: E, G#, B, E is identical to E, G#, B and is also identified as an E Major chord.

The repeating pattern of note intervals allows us to drastically reduce the number of possible note permutations. If it weren't for this pattern, there would be 220 possible permutations of 3-note chords within a 12 note scale: for 12 elements (n=12), take 3 (k=3), using the equation n! / k!(n - k)!.

Improvements

• Instead of saying a chord is G# / Ab it would be better to differentiate between the two. See this link on StackExchange for more context.

Contributions

Contributions & collaboration are very much welcome. This is meant to be a fun side-project that stemmed from an interest in how the chord-identifier works in Logic Pro. This initial prototype is likely a naive solution, and recommendations for alternative approaches are most definitely welcome!