Hearddle
Play the tones, then tap the one that's off-pitch. 10 rounds, getting harder.
About Hearddle — spotting the off-pitch tone
Hearddle trains odd-one-out pitch detection — picking the single tone that sits slightly off from its neighbours. Catching a note that is a touch sharp or flat is exactly what a choir singer does when one voice strays, or what you do when an instrument slips out of tune partway through a piece.
Ten rounds each play a small group of tones with one off-pitch member. Tap the odd one out. The gap shrinks as you go, so every round asks a little more of your ear.
How small a difference can anyone actually hear? Our guide to the just-noticeable difference explains the limits of pitch resolution and how practice moves them. See all our ear-training guides to dig deeper.
What Hearddle trains
Hearddle works your odd-one-out pitch detection: hearing a small group of tones that are meant to be identical and catching the single one that sits off. It is a comparison task, not a naming task, so no musical vocabulary is required. What it asks for is resolution: noticing that one tone does not belong. The gap shrinks as the puzzle goes on, so what felt obvious at the start becomes fine work by the end.
How to play
Press Play the tones to hear the round. The group starts at three tones and grows to seven by the last round; each pad lights as its tone sounds. Tap the pad you think is off. There are ten rounds and one answer per round: replay the group as often as you like, but once you tap, that round is settled. Get it wrong and the correct pad is highlighted and replayed on its own before you continue, so every miss still shows you what the difference sounded like.
How scoring works
Your score is simply how many of the ten rounds you got right. The difficulty is not random: the off-pitch tone starts about a third of a semitone away and narrows smoothly to roughly eight cents by the final round, near the limit of what an untrained ear resolves. The group also grows, so late rounds combine a smaller difference with more tones to hold in mind. The ramp is the same every day, so your score compares fairly against your own previous days. Six correct out of ten earns the day towards your streak.
What your score means
Treat the number as a band rather than a measurement:
| Outcome | Rough interpretation |
|---|---|
| 9-10 of 10 | Resolving differences near the fine end of the ramp |
| 6-8 of 10 | Comfortable early, losing the smallest gaps late; six is still enough to earn the day |
| 5 or fewer | Work on the early rounds; try headphones first |
Losing the last two rounds is normal. Round one is the gentlest of the ten: three tones and the widest gap on the ramp, so a miss there usually says more about your listening conditions than about your ear.
Common mistakes
The first mistake is deciding on one hearing. Replay the group twice; the odd tone often only stands out on the second pass. Second is listening for loudness rather than height; the tone that catches your attention is not always the one that is off. Third is the first-and-last trap: the opening and closing tones are easiest to remember, so they get picked more often than they deserve. Fourth is racing the late rounds, where seven tones and an eight-cent gap need patience, not instinct. Finally, noise and small speakers mask the fine differences the last rounds are built on.
Practice progression
(5 min, beginner) Play each group twice and say the position out loud before you tap. (10 min, intermediate) Answer the first six rounds on a single hearing, saving your replays for the fine ones. (weekly) Follow Hearddle with Hearfork, which asks you to spot the off-pitch tone and then judge how far off it was, and read the just-noticeable difference guide.
The science behind it
The late rounds probe the frequency difference limen, the smallest change in frequency a listener can reliably detect. Classic psychoacoustic work established that this limen depends heavily on how long the tone lasts, which is why short tones are harder than sustained ones. Training moves the threshold: non-musicians' pitch discrimination thresholds measured several times larger than classical musicians', and improved after only a couple of hours of practice. Our guides on cents and frequency in hertz explain the units used here.
Limitations
Hearddle is a game and an informal self-check, not a clinical or diagnostic tool. Browser audio, headphones and room noise change what reaches your ear, so scores from different devices are not comparable. Ten rounds is a small sample, and a low score can mean a noisy room as easily as a limit of your hearing. If you have a concern about your hearing, see an audiologist.
Where it shows up
Catching the one tone that does not fit is a working skill long before it is a musical one. A choir director hears twenty voices and knows immediately which part has drifted flat, then hears which singer inside it is pulling. A piano tuner works almost entirely in this mode, comparing neighbours and listening for the beating that appears when two pitches are close but not identical. The same attention shows up outside music: a mechanic notices one cylinder firing differently from its neighbours, an engineer hears a single bearing whining out of an otherwise even machine, a parent picks their own child's voice out of a playground. In each case nothing is named. Something in a set of near-identical sounds is not matching, and the ear reports it before any analysis begins. The same shape of task turns up in maintenance and inspection work: a technician walking a row of pumps hears the one that has gone slightly off, a cyclist notices a single spoke ringing at the wrong pitch, a rail inspector listens for the wheel that answers a hammer tap differently from its neighbours. Anyone tuning a stringed instrument does it in miniature every time they play two strings together and listen for the slow beating that means they have not quite matched. In each of these the set is supposed to be uniform, and the useful signal is the one member that is not. Hearddle isolates that ability and pushes it towards its limit, which is why the last rounds feel less like a puzzle and more like a measurement.
Ready to find the odd tone? Ten rounds, one tap each, about two minutes, and a new puzzle tomorrow.
Frequently asked questions
How many rounds are there?
Ten. The group grows from three tones in the first round to seven in the last, and the off-pitch tone gets progressively closer to the others.
Can I change an answer?
No. One tap settles the round. You can replay the group as often as you like before you commit.
What happens when I get one wrong?
The correct pad is highlighted and its tone replayed on its own, then you continue. Hearing the answer in isolation is the most useful part of a miss.
How small does the difference get?
The final round is about eight cents, well under a tenth of a semitone. Missing that one is ordinary.
Do I need musical training?
No. You never name a note or an interval, only compare tones to each other, so the task works the same whether or not you read music.
Related reading & games
- How small a difference can you hear?: the threshold the late rounds are built around.
- Hearfork spots the off tone and then measures the gap; Hearmber asks only higher or lower.
- What pitch is, plus the full set of ear-training guides.
Sources: Moore, B. C. J. (1973), Frequency difference limens for short-duration tones, Journal of the Acoustical Society of America 54(3), 610-619; Micheyl, C., Delhommeau, K., Perrot, X. and Oxenham, A. J. (2006), Influence of musical and psychoacoustical training on pitch discrimination, Hearing Research 219(1-2), 36-47.
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