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Hooktheory Aria: The New AI MIDI Generation Tool in HookPad

HookTheory is a music software company built for songwriters and composers. Their core interface is a colorful MIDI piano roll that supports melodies and chord charts. They have two major products available, including a free song directory called TheoryTab and a music creation tool called HookPad.

TheoryTab hosts over 50,000 user generated transcriptions of popular songs across every genre. Site visitors can search for an artist, pick a song, and explore the underlying chords + melodies to see how they're built. Think of it as a kind of MIDI Wikipedia.

HookPad is the tool that anyone can use to compose original music and create transcriptions to contribute to TheoryTab. Songwriters can capture new ideas quickly and share them with others through the MIDI export features.

In June 2024, the company rolled out a brand new generative AI MIDI feature called Aria. We'll be unpacking that new feature below, along with a general overview of all the other cool stuff that HookTheory has to offer.

Aria: HookTheory's new AI MIDI generator

Aria is a HookPad feature developed in partnership with Chris Donahue, a professor at Carnegie Mellon University and part-time research scientist at Google DeepMind, using his open-source Anticipatory Music Transformer

With the click of a button, Aria generates MIDI chord progressions for existing melodies, writes melodic accompaniment for chords, and can create chord + melody compositions out of thin air. 

Users select a region in their HookPad project and then ask Aria to make suggestions for alternative ideas. The model looks at surrounding measures and composes chords and melodies to fit into that context. 

How did HookTheory train the Aria model?

The Anticipatory Music Transformer was originally trained on the Lakh MIDI dataset. That's a collection of ~176k MIDI files under a creative commons license. 

HookTheory fine-tuned the AMT on their own database of 50,000+ MIDI tracks. These are chord and melody transcriptions of popular songs from major artists and composers across every genre. 

You might me thinking to yourself "Should a company selling commercial software pay traditional sheet music licensing fees to train on UGC transcriptions of popular songs?"

It can be done. Lemonaide Music trained their model on music that they licensed. That's why they are Fairly Trained certified. Hooktheory's cofounder Ryan has clarified that Aria does not train on private Hookpad projects and they will never use private user data for anything without permission. 

Compared to the disruptive potential of instant song generation apps like Suno and Udio, a generative MIDI feature like Aria seems relatively harmless. 

Still, there's a cohort of people who believe any commercial product trained on copyright material should make efforts to license that music. 

Overall, HookTheory has made a valuable contribution to the generative AI MIDI software niche. Aria creates new MIDI ideas quickly, with better output than free tools like OpenAI's Musenet or Google's Magenta Studio suite.

Lemonaide and Logic Pro's AI Session Musicians were previously the only serious genAI MIDI products on the market. Hookpad's Roman numeral notation puts them in the running with other big MIDI software apps like Captain Chords and Scaler 2. Aria gives HookTheory a leg up in the software that race.

How to use TheoryTab

You don't have to buy HookPad to enjoy what HookTheory has to offer. TheoryTab offers a free collection of over 50,000 song transcriptions to explore.

Visit their database and search for a song or artist. When you find one that interests you, pop it open and press play on the embedded widget. There's a YouTube player embedded on the right side of the page. The MIDI piano roll will run visually while the audio from the YouTube video plays.

We've loaded the song Flim by Aphex Twin in the example below:

TheoryTab interface
TheoryTab for an Aphex Twin song

The melody, chords, and keyboard voicing tells you a lot about a song's structure. It's hard to understand the experience until you visit the site and try it yourself.

Switch from YouTube to Piano mode and you'll hear what the raw MIDI sounds like. I've found that the melody and chord progressions in their collection are usually accurate. The rhythm applied to the chords make no effort to resemble the original track. This simplifies the arrangement process for people making the tabs.

Once you have piano selected, you can start to mess with the song's key signature. To do that, simply click on the circle icon labeled Key. You'll notice that the color blocks stay the same, while the notes at the far left edge are updated.

The seven notes of your scale are assigned to the seven colors of the rainbow, as shown below. Each colorful block-row of the piano roll is defined by the key. If you’re familiar with the Fold tool in Ableton, it works in a similar way:

HookTheory tab
Key Signature Selection

TheoryTab lets you change a song’s key signature, impacting the chords and melody.

Basically, the MIDI notes are anchored to scale degrees instead of notes. So when you update the key signature, the scale degrees stay the same but the note assignments change. That's why the colored blocks don't move.

Chord Progression Notation

Under the piano roll, you’ll find chord blocks that adhere to the same color coding system. A note that’s blue in the piano roll is also blue on its chord block. Leverage the color coding to intuitively see the way melodies create and resolve tension from one chord to the next.

Chord progression
Chord progression

As the illustration above shows, each chord is assigned a Roman numeral. These represent the scale degree of the chord's root note. While the chord type may change, the scale degree does not, and so the Roman numerals represent a kind of musical constant for your progression.

For example, In the key of C major, you would say the VI chord is A minor. Then if you change to the key of G major, the VI chord would become E minor. In other words, the numeral stays the same as the relative chord is updated.

As a side note, HookTheory's chords are sometimes written as Inversions, with a slash between the primary chord and the bass note. This just means they put that note in the bass of the piano, likely because that's where it was in the original song arrangement. For the most part, chords are played in their root position.

Chord and melody metrics

At the end of each song page, TheoryTab offers chord and melody metrics that rank on five factors - chord complexity, melodic complexity, chord-melody tension, chord progression novelty, and chord bass melody.

These metrics are aggregated to form a geometric representation of the song’s overall complexity. To learn more about how this data is measured, check out there song metrics page.

HookPad: Creating Your Own Music

HookPad is a browser application for songwriters. You can use it to create your own music and audition different chord/melody ideas quickly. It resembles the MIDI piano roll portion of a DAW, but with tools geared toward songwriters rather than audio engineers. Drag MIDI from the app to your DAW as part of your music production workflow.

HookTheory Magic Chord
HookTheory Magic Chord Pallette
Hookpad Magic Chord Button

For those of you who follow our blog, we couldn't leave out the magic chord button. This feature analyzes your existing progression and chooses the next one on your behalf. It's arguably a more usable version of apps like Continue from Magenta Studio or the generative MIDI from MuseNet.

If the you want some help becoming familiar with the interface or learning the music theory concepts that drive it, check out Hooktheory II, an iOS application they published. This would be a great place to start, especially for beginners.

But wait... there's more! Remember, these guys have been around for a decade.

HookTheory was founded in 2013 by a trio of PhD students at UC Berkeley; Ryan Miyakawa, Chris Anderson, and David Carlton. The press says that their long friendship has been based on a shared interest in music and software. Maybe that's why the company has endured and continued to innovate all these years.

With almost a decade of software development under the belt, here are some of the fun things their team has published, beyond TheoryTab and Hookpad.

The Chordle Game


Remember when Twitter went crazy for Wordle? The game's buzz has kind of died down, but the premise is still fun. HookTheory created a music theory Wordle, to help you with your ear training and chord logic.

Chordle provides a key signature and asks you to guess which triad it’s thinking of. It lets you know which notes are right or wrong until you guess it (or fail). It's a one-puzzle-per-day type of game, so you don't have to worry about getting sucked into it addictively.

Chord Crush

Want to sharpen your ability to recognize chord progressions on the fly?

HookTheory offers a gamified ear training app called Chord Crush. It's a free puzzle game that challenges you to name as many chords in a progression within a limited time. Have a look at the demo below:

Key Cheat Sheets

HookTheory's most popular chords

This HookTheory resource lets you study the different ways a key signature has been used over time. You can find the 20 most popular chords in each key, according to the training set.

Navigate to a particular chord progression and you'll discover all the songs in their database that use it. Listen to the different ways they use melodies over the same progression and you can train your ear to imagine different options during your own creative sessions.

Infographics for chord popularity

Chord progressions
Chord progressions

If you're trying to capture a retro sound from a specific decade, don't sleep on this HookTheory infographic collection. You'll be able to get quick ideas for your own music and can experiment within TheoryTab, rather than having to recreate something in your own DAW or download a MIDI file.

Classroom Guides for Hookpad

In the off chance that you’re a music educator, HookTheory does also offer a virtual classroom environment. This is a great resource for teaching students remotely or in a computer lab. Create lessons and have them login with HookPad to review their assignments.

For more tips on how to use the software, check out HookPad's youtube playlist called the Beginners Guide. Here's the first video from the series, to get you started. Enjoy!

If you want to see how the app compares to its competitors, check out this feature-by-feature roundup of alternatives. The best option is probably Chordify, but I found their interface to be less user friendly and a bit bland compared to HookTheory.

That's it for this week. Hope you've enjoyed the songwriting resources. Enjoy!


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