Groove Number

Anyone who has tried to copy the shuffle of a classic house record knows the problem. Swing is something you hear long before you can name it, yet sequencers and quantize menus want a number. Groove Number, a music analysis utility from developer Joshua Langberg for iOS, closes that gap. It analyzes a track and reports how swung it is as a single percentage: 50% for dead-straight timing, roughly 66% for full triplet swing. That range matches the swing convention many producers know from drum machines and DAW swing controls, so the readout arrives in a language beat-makers already speak.

Swing is the headline. The app also estimates BPM and musical key on the device, which puts it in crowded territory. Tempo and key detection ship inside most DJ software and plenty of free apps. Langberg’s differentiation comes from the swing measurement and from how much of the analysis the app exposes rather than hides. A swing grid, a mel-scaled spectrogram and a chromagram sit behind the headline figures, and the groove can leave the app as a MIDI clip with the timing intact.

The positioning is unusually candid. Its stated focus is four-on-the-floor and electronic music, with less reliability on live, acoustic or rubato material. That honesty narrows the audience to producers, sample collectors and DJs working in electronic genres, but it also tells those buyers this tool was built for them.

The business model is equally plain: one payment of $1.99, with no account, no ads and no tracking. Reception data is too thin to lean on. The App Store rating is 5.0 out of 5 from one rating, too little to support claims about accuracy. That leaves the design and the feature set to make the case on their own, and on paper they make a coherent case for a narrow audience.

• Swing percentage: Expresses groove as one figure on a 50% (straight) to roughly 66% (triplet) scale.
• On-device BPM detection: Includes an octave guard against half- and double-time errors, plus halve, double and tap-tempo overrides.
• Key detection with confidence: Reports a confidence level alongside the runner-up key, so the result reads as a ranked estimate instead of a flat verdict.
• Flexible audio input: Accepts mp3, m4a, aac, wav, aiff and flac files, recorded clips, or the live microphone with a VU meter.
• Four result views: A meter readout, a swing grid plotting each onset against the straight grid, a mel-scaled spectrogram and a chromagram.
• MIDI groove export: Saves the groove as a MIDI clip with the swing built into the note timing.
• Siri and Shortcuts: Siri can start a recording or live listening and report the last result. A Shortcuts action can tag a folder of samples by BPM.
• Clean pricing: $1.99 once, with no account, ads or tracking.

The Swing Measurement

Reducing swing to one number is the app’s boldest decision, and mostly the right one. A percentage is portable. It can be typed into a sequencer’s swing field, written into a sample’s filename, or compared across a crate of records. The 50-to-66 scale also teaches as it measures, because its endpoints correspond to feels any producer recognizes: a rigid sixteenth-note hi-hat at one end, a lilting triplet shuffle at the other.

The cost is compression. Real grooves are rarely uniform. Hi-hats can swing while a kick stays rigid, and the feel can drift across a bar. A single figure averages those details away. Groove Number’s answer is the swing grid, which plots every detected onset against the straight grid. That view shows whether a 58% reading reflects consistent placement or an average of scattered hits, which is the difference between a programmed shuffle and a loose human pocket. The headline number is the summary; the grid is the evidence. That pairing is the smartest structural choice in the app.

Tempo and Key: Built to Admit Doubt

The classic failure in tempo detection is the octave error: a 140 BPM track read as 70, or a half-time beat reported at double speed. The octave guard targets that problem directly, and the halve, double and tap controls concede that no algorithm wins every time. Automatic first, manual override one step away, is the correct hierarchy. Tap tempo in particular respects the fact that a DJ’s ears often settle tempo faster than any correction menu.

Key detection gets the same treatment. A confidence level and runner-up key turn an opaque answer into a ranked guess. Key estimators commonly confuse closely related keys, such as a major key and its relative minor, so surfacing the second candidate gives harmonic mixers something to check against. We prefer a tool that admits doubt over one that projects false certainty, and Groove Number is built around admitting it.

Showing the Working

The four result views divide cleanly by audience. The meter readout serves anyone who wants a number and nothing more. The swing grid serves producers studying feel. The mel-scaled spectrogram, a frequency display spaced to follow how human hearing perceives pitch, shows where energy sits across a track. The chromagram, which folds that energy onto the twelve pitch classes, is the natural companion to key detection. If the app calls a track F minor, the chromagram is where a user can check whether F, A-flat and C dominate. Bundling these views into a $1.99 utility adds value, and it gives the app a second use as a teaching aid for anyone learning to read audio visually.

Getting the Groove Out

MIDI export is the feature that turns analysis into production. A clip with the measured swing built into its note timing can serve as a timing reference inside a session, or as source material for DAWs that can extract a groove from MIDI. That shortens the path from “how swung is this record?” to “make my track sit like that” without re-entering numbers by hand. For producers chasing the feel of a reference track, this is the main reason an electronic producer might buy it.

Automation for Sample Libraries

Siri control suits hands-busy moments: a producer at a controller, a DJ behind decks, someone who wants the last result read back without picking up a device. The Shortcuts folder-tagging action is the most practical feature for a large group of users, namely anyone with a sprawling, badly labeled sample library. Batch tempo tagging is tedious work, and handing it to an automation is exactly what Shortcuts exists for. Extending the same batch treatment to key and swing would be the logical next step and would make the app a fuller library-organization tool.

Where It Falls Short

The stated weakness matters. Live, acoustic and rubato material, from jazz trios to funk bands to solo piano, is where swing is most interesting and most variable, and it is where the app is less reliable. A jazz ride cymbal pattern is the textbook example of swing, yet a tool tuned for four-on-the-floor grids will struggle with a tempo that breathes. The live microphone input sharpens the irony. Pointing a phone at a band is tempting, but a band is the use case the app flags as weak. Pointing it at a club system playing house is a far better bet. For electronic producers this barely registers. For jazz students hoping to quantify their heroes, it is a hard limit worth knowing before spending even $1.99.

The interface, as the feature set lays it out, splits a dense dataset into four distinct views instead of one crowded dashboard. On an iPhone screen, that separation is the right call. The meter readout and VU meter borrow the visual vocabulary of studio hardware, a familiar language for this audience that should make levels and results readable at a glance. The swing grid is the most valuable visual idea in the app because it makes an abstract property, timing deviation, visible hit by hit. Spectrograms and chromagrams are information-dense by nature, and their detail will read better on an iPad than on a phone.

Performance can only be judged at the design level. All analysis runs on the device, which means no uploads, no server queue and no dependence on a connection for core features. Onset detection, spectrograms and chromagrams are well-established signal-processing tasks within comfortable reach of current Apple hardware. A full-length flac file naturally demands more work than a short recorded clip, and live listening is a continuous real-time load.

Groove Number targets iOS, and each device suits a different job:

• iPhone: The natural home for the live microphone and recorded clips. Capturing a groove in a club, record store or rehearsal room is a phone-first workflow. The smaller screen is the weak point for spectrogram and chromagram detail.
• iPad: The larger canvas suits the swing grid and chromagram, making it the strongest option for study and teaching, or as a studio companion beside a controller.

Input differs accordingly. Tap tempo fits a touchscreen naturally, since a finger on glass keeps time the way a hand on a table does. Siri is available across iOS. Pricing is $1.99 once with no account.

Groove Number measures something most analysis tools ignore and presents it in the unit producers already use, but the narrow genre focus and thin reception keep it from a broad recommendation. The swing percentage is the hook; the supporting design is what makes it usable for a narrow audience. The swing grid backs the number with evidence, the tempo and key detectors admit uncertainty instead of hiding it, and MIDI export turns a measurement into something a producer can work with. The limits are just as clear: this is a tool for grids, not jazz trios, and buyers chasing the swing of live players should look elsewhere.

For its intended audience, the value case is simple. At $1.99 with no subscription or account, the cost is low for the narrow job it does. Reception is too thin to confirm accuracy across a wide catalog, which keeps it out of top-tier territory. We can recommend it only to electronic producers who need a quick swing readout and understand the genre limits.