Chord Engine¶

The Chord Engine is MAGDA's built-in chord analysis, suggestion, and generation device. It detects chords from incoming MIDI, identifies the musical key, and suggests what chord to play next — all in real time.

Overview¶

The Chord Engine is a MIDI device that lives on an instrument track's FX chain. Unlike a typical plugin panel, its interface is also embedded directly in the Piano Roll — chord suggestions appear alongside your notes, and you can drag chords straight onto the timeline. This tight integration between harmonic analysis and note editing is central to the workflow.

It analyses incoming MIDI notes and provides:

Real-time chord detection — identifies the chord you're playing
Key and scale detection — determines the tonal centre from your playing
Context-aware chord suggestions — recommends chords based on music theory and voice leading
AI-generated progressions — uses a language model to compose chord progressions in a given style
Drag-and-drop to Piano Roll — drop suggestions directly onto the timeline as MIDI notes with chord annotations

The device has two tabs: K&S (Krumhansl-Schmuckler analysis and suggestions) and AI (LLM-generated progressions).

K&S Tab¶

Chord Engine — K&S Tab

The K&S tab uses the Krumhansl-Schmuckler algorithm to detect the key from your playing and generate chord suggestions from music theory rules. The interface has three columns:

Column	Content
Chord (left)	Currently detected chord, recent history, and a Play button for auditioning
Suggestions (centre)	Grid of chord suggestions with Roman numeral degrees
Key / Scale (right)	Detected key, matching scales, and scale browser

Chord Detection¶

Play notes on the track and the panel displays the detected chord name in real time. Detection uses pitch-class set matching against a library of known chord shapes (triads, sevenths, ninths, elevenths, thirteenths, augmented, diminished, suspended, and slash voicings).

Recent chords appear in the History section.

Key Detection¶

The detected key (e.g. "D# minor") is shown at the top of the right column. It uses the Krumhansl-Schmuckler key-finding algorithm:

A pitch-class histogram accumulates every note you play, weighted by an exponential time decay (recent notes matter more; decay constant is 5 seconds).
The histogram is correlated against Krumhansl major and minor profiles — empirically derived distributions of pitch-class frequency in tonal music.
All 24 possible keys (12 roots x major/minor) are scored. A small bias toward the third of each candidate helps disambiguate major vs minor.
The highest-scoring key wins.

Scale Detection¶

Below the key, the panel lists the top matching scales (Ionian, Aeolian, Dorian, Mixolydian, Pentatonic, etc.), ranked by how well your pitch content matches each scale's note set.

Click a scale to see all diatonic chords built from it
Shift-click a scale to select it for filtering (highlights green). Multiple scales can be selected — their pitch classes are merged to filter suggestions

Suggestion Generation¶

Suggestions are generated from:

Diatonic candidates — chords built from scale degrees I–VII, with optional extensions (7ths, 9ths, 11ths, 13ths)
Non-diatonic candidates — modal borrowings, secondary dominants, and altered chords
Voice leading — suggestions are voiced to minimise movement from the last chord played

Recently played chords are filtered out so suggestions always point forward.

Control	Description
Nov (Novelty)	Balance between diatonic (0%) and chromatic (100%) suggestions
7th	Toggle seventh chord suggestions
9th	Toggle ninth chord suggestions
11th	Toggle eleventh chord suggestions
13th	Toggle thirteenth chord suggestions
Alt	Toggle altered/non-diatonic chord suggestions

AI Tab¶

Chord Engine — AI Mode

In AI mode, a language model generates full chord progressions based on a text description. Type a prompt describing the style, mood, or harmonic flavour you want, and the AI returns a sequence of chords.

Using AI Suggestions¶

Type a description in the text field. This can be a qualitative mood description (e.g. "soulful and jazzy", "dark ambient") or a functional one using chord grades (e.g. "I-iv-V7 progression", "ii-V-I turnaround")
Press Enter or click the send button
The AI returns one or more labelled progressions as rows of chord buttons
Click a chord to audition it
Drag a chord onto the Piano Roll to place it as MIDI notes

AI progressions are labelled with a short description (e.g. "Dim pull with warm iv and V7", "Backdoor cadence into Dim").

AI with Key Context¶

The AI receives the currently detected key as context, so its suggestions are harmonically relevant to what you've been playing.

Suggestion Pipeline¶

The K&S tab's suggestion engine uses the following pipeline:

flowchart TD
    A["MIDI Note Input"] --> B["Pitch-Class Histogram<br>(time-decayed, τ = 5s)"]

    B --> C["Krumhansl-Schmuckler<br>Key-Profile Correlation<br>12 rotations × major/minor/modal"]

    C --> D["Detected Key + Mode"]

    D --> E["Diatonic Candidates<br>Scale degrees I–VII<br>+ 7ths / 9ths / 11ths / 13ths"]
    D --> F["Non-Diatonic Candidates<br>Modal borrowings<br>Secondary dominants<br>Alterations / Slash chords"]

    E --> G["Mix by Novelty<br>0.0 = diatonic, 1.0 = chromatic"]
    F --> G

    G --> H["Filter Recently Played Chords"]

    H --> I["Voice-Leading Optimizer<br>Minimize centroid distance<br>from last played chord"]

    I --> J["Top-K Suggestions"]

    style A fill:#2d2d2d,stroke:#7c4dff,color:#fff
    style D fill:#1b5e20,stroke:#4caf50,color:#fff
    style G fill:#4a148c,stroke:#ce93d8,color:#fff
    style J fill:#0d47a1,stroke:#42a5f5,color:#fff

Chord Timeline¶

Chord Timeline in Piano Roll

When a Chord Engine is present on a track, the Piano Roll automatically shows a chord row above the note grid. This row displays chord annotations that are linked to their MIDI notes.

Placing Chords¶

Drag a chord from the suggestions grid and drop it onto the Piano Roll:

Drop sets the start position — a blinking indicator appears
Move the mouse to preview the chord length
Click to confirm the length, or press Enter to use the default length
Press Escape to cancel

The dropped chord creates both MIDI notes and a chord annotation in the timeline. These are linked — moving, resizing, or deleting the notes automatically updates the annotation.

Detecting Chords¶

Click the refresh button in the chord row to auto-detect chords from existing notes. The detection scans notes at each bar boundary, identifies chords with 2+ simultaneous notes, and creates linked annotations.

Note Tracking¶

Chord annotations track their associated MIDI notes in real time:

Move notes — the annotation follows
Resize notes — the annotation length updates
Delete notes — the annotation shrinks or disappears
Transpose notes — the chord name re-detects automatically
Undo/redo — annotations revert along with their notes