MIDI Drum Indexer

A search tool for the 800,000 Drum Percussion MIDI Archive — the well-known collection of MIDI drum patterns originally shared on music production forums. While it was built to index this collection, it can be used to scan any collection of drum midi files.

The archive contains ~764k MIDI files organized in folders by genre, but with inconsistent naming and no searchable index. This tool parses every file, extracts musical features, stores them in a SQLite database, and provides a browser-based UI to search, filter, and audition patterns instantly using sampled sounds for all instruments found in the "800k" collection.

What it does

• Indexes MIDI drum files — extracts time signature, tempo, swing feel, instruments used, and beat positions from each file
• Detects time signatures from the music itself rather than trusting MIDI metadata (which is often wrong — e.g. waltz patterns marked as 4/4)
• Extracts tempo from filenames when encoded (common pattern: 120_RockBeat.mid)
• Identifies instruments using the General MIDI percussion map (58 unique drum notes across 13 categories)
• Builds a searchable beat grid — every note quantized to a 16th-note grid slot

Search features

• Time signature — filter by detected meter (4/4, 3/4, 6/8, 5/4, 7/8)
• Tempo range — min/max BPM slider
• Feel — straight or swing
• Genre — filter by archive folder (Jazz, Rock, Latin, Funk, Blues, etc.)
• Instruments — tri-state filters (must have / must not have / don't care) at both category and individual instrument level
• Beat pattern — clickable 16th-note grid: specify "kick on 1 and 3, snare on 2 and 4" and find patterns with exactly that groove — no extra hits on those instruments, so you get clean matches rather than fills
• Type — pattern vs. fill
• Text search — filename and path substring matching
• Beat grid visualization — click any result row to expand an inline beat grid showing all instruments and hit positions, with velocity indicated by opacity

In-browser playback

Results can be auditioned directly in the browser using bundled drum samples (48 instruments, ~290KB total) played back via Tone.js. Covers the full GM percussion map including kit drums, Latin percussion, shakers, bells, and more. Playback supports looping and tempo adjustment.

Layout

The UI uses a stacked over/under layout — search filters spread across the full width on top, results table below. A draggable resize handle between them lets you adjust the split to suit your screen. Filters are arranged with dropdowns inline on the first row, then beat grid and genre on the left with instruments in a column on the right.

Getting started

1. Download the MIDI archive

Download the 800,000 Drum Percussion MIDI Archive. It's a single zip file (~1.5 GB). Unzip it somewhere on your machine.

2. Clone this repo and install dependencies

git clone https://github.com/caedmon5/midi_drum_indexer.git
cd midi_drum_indexer
python3 -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt

3. Run the app

python3 app.py

Open http://localhost:5000 in your browser. On first run you'll be taken to a setup page that walks you through pointing the tool at your archive and building the database. The curated genre folders (~19k files) index in about 15 seconds.

Command-line indexing (optional)

You can also build the database from the command line if you prefer:

python3 indexer.py --archive /path/to/800000_Drum_Percussion_MIDI_Archive[6_19_15]

The two massive collections (GM MIDI Pack at 360k files and Superior Drummer 2 at 425k files) are skipped by default. To index everything, pass --all. To index specific folders: --folders "Jazz,Blues Drums,Bossa".

The indexer is idempotent — re-running it skips files already in the database.

Architecture

File	Purpose
indexer.py	Walks the archive, processes files in parallel, writes to SQLite
analyzer.py	MIDI parser and feature extraction (time sig detection, swing analysis, beat grid quantization)
app.py	Flask web app with search API, MIDI file serving, and setup wizard
schema.sql	Database schema (5 tables) and GM percussion instrument seed data
generate_samples.py	Generates the bundled drum sample mp3s via numpy synthesis
templates/setup.html	First-run setup wizard (archive path, database build with progress)
templates/index.html	Search UI with filters, beat grid editor, results table
static/player.js	Tone.js sample-based MIDI playback engine
static/samples/	48 drum sample mp3s (~290KB total)
static/style.css	Dark theme responsive layout

Known limitations

• Time signature detection is heuristic — it infers meter from pattern length and folder name hints, which works well for clear cases but can misclassify ambiguous patterns (e.g. a 4-beat pattern from a waltz folder vs. a true 4/4 pattern)
• Swing detection relies on hi-hat/ride spacing and may be inaccurate for patterns without a steady timekeeping instrument
• Brush kit note mappings (Vintage/Studio/Modern Drummer) use non-standard MIDI notes (81-92) that can't be decoded from GM alone — these are tagged by filename only
• Tempo from MIDI metadata defaults to 120 BPM when no tempo event is present, which is the MIDI standard default but often not the intended tempo

Tech stack

Python 3, mido, SQLite, Flask, Tone.js, @tonejs/midi. No build step — vanilla JS and Jinja templates.

License

This tool is for indexing and searching MIDI files you already have. The MIDI archive itself has its own distribution terms.