Heartween
Find the pitch exactly halfway between tone A and tone B. 3 tries.
About Heartween — hearing the pitch in between
Heartween trains interval interpolation — sensing the pitch that sits exactly between two others. Judging the middle of a gap sharpens your feel for how big an interval is, the same instinct that lets a singer pitch a harmony or a player find a note without hunting for it.
Hear tone A and tone B, then move to the pitch halfway between them. You get three tries to place that midpoint as precisely as you can, learning after each attempt whether you landed high or low so the next one can close in.
The space between two pitches is an interval, and hearing it is a learnable skill. Our guide to musical intervals breaks down how they sound and why they matter. Find every topic in our ear-training guides.
What Heartween trains
Heartween works your interval interpolation: finding the pitch that sits exactly halfway between two others. It is a harder question than "which of these is higher", because there is no answer to recognise, only one to construct. You hold both ends in mind, imagine the middle, then produce it. That is the instinct a singer uses to place a harmony inside a gap they can hear but cannot name.
How to play
Press Tone A and Tone B to hear the two ends. Move the slider between Lower and Higher, press Hear my guess to audition it, and press Lock in guess when ready. You get three tries. After each one you are told only which way to move: a bit higher, a bit lower, or spot on once you are within about a tenth of a semitone. When the round finishes you see the true middle in hertz alongside your best guess, and True middle vs. your best plays the two back to back.
How scoring works
Your result is your best single try, expressed as a closeness percentage. The distance is measured in cents, not hertz, and that matters here more than anywhere: the true middle is the geometric mean of the two frequencies, the point the same number of cents from A as from B. It always sits below the plain numerical average of the two hertz values. With three tries and direction-only feedback, the useful strategy is to guess deliberately and then halve the remaining error.
What your score means
Read the percentage as a band:
| Outcome | Rough interpretation |
|---|---|
| Spot on, 98% or better | The round ends there; you are hearing the midpoint, not calculating it |
| 85% or better | Good sense of the gap, and the score that earns the day; the last correction was coarse |
| Below 85% | Likely aiming at the numeric average rather than the heard middle |
Three tries is a small sample. The trend across a fortnight says more than any single day.
Common mistakes
The classic error is splitting the numbers instead of the sound. Averaging the two frequencies arithmetically always lands you above the true middle. Second is replaying only one end; you need both in mind at once, so play A, then B, then A again. Third is spending a try on a position you never auditioned, which wastes a third of the round. Fourth is over-correcting after a hint and sailing past the middle from the other side. Finally, a wide pair on small speakers loses the bottom end, pulling your sense of the middle upward.
Practice progression
(5 min, beginner) Play A, B, A, then hum the middle before touching the slider, and move to what you sang. (10 min, intermediate) Commit your first lock without auditioning it, to find out what your unaided midpoint sense is worth, then use the other two tries to close in. (weekly) Pair Heartween with Hearspan, which reproduces a whole interval from a new starting tone, and read musical intervals explained.
The science behind it
Halving a gap by ear is a relative-pitch task: you work with the distance between two tones, not with either tone alone. Research comparing interval perception across pitch, loudness and brightness found that interval acuity in pitch is not itself remarkable once thresholds are expressed in common units; what is unusual is the very fine frequency resolution underneath it. Your midpoint sense is ordinary interval judgement running on an unusually precise dimension. Our guides on cents and the octave explain why the middle is a ratio, not an average.
Limitations
Heartween is a game and an informal self-check, not a clinical or diagnostic tool. Browser audio, headphones and background noise all shift what you hear, so results from different devices are not comparable. One day gives you three tries on one pair of tones in one range, which is far too little to describe an ability. If you have a concern about your hearing, see an audiologist rather than a daily puzzle.
Where it shows up
Finding the pitch inside a gap is ordinary work for anyone who sings or plays without notation. A backing vocalist hears the melody and the bass and has to place a third voice between them that belongs to neither. A guitarist bending a string towards a target passes through the whole space in between and has to stop in the right place, a midpoint judgement made in motion. A fretless bass or violin player has no marks to aim at and finds every note by dividing a distance they can hear. Outside music the same interpolation appears whenever you match a pitch you have only inferred: copying the rise and fall of a question in a language you are learning, or tuning your voice into the middle of a group singing in unison. A trombonist moving between two known slide positions has to find the one in between without a marker to stop at. A choir director demonstrating a part sings a note nobody in the room has played yet, placed inside a chord they can hear. Even a piano tuner setting a temperament works by dividing a span into steps that have to come out even by ear before any of them is checked. What these share is that the answer is never presented to you. You have two references, and you build the thing between them. That is a harder operation than recognition, because there is nothing to compare your candidate against except your own sense of the gap. It is also the reason arithmetic is such a tempting shortcut here and such a poor one: the middle you can calculate and the middle you can hear are not the same number, and only one of them is the one you have to sing. Heartween strips that to its simplest form: two tones, one gap, three chances to find the middle.
Ready to find today's middle? Two tones, three tries, about a minute, and a new pair tomorrow.
Frequently asked questions
How many tries do I get?
Three. The round also ends early if a guess lands within roughly a tenth of a semitone of the true middle, which registers as spot on.
Why is the middle not the average of the two frequencies?
Because pitch is heard as a ratio. The middle you hear is an equal number of cents from each end, which is the geometric mean and always sits below the arithmetic average.
Why does it only tell me higher or lower?
Direction-only feedback keeps each try a real decision. A numeric error readout would let you solve the puzzle by arithmetic instead of by ear.
Can I replay tone A and tone B freely?
Yes. Only locking in a guess costs a try, and hearing both ends in alternation is the most useful habit here.
Does everyone get the same pair?
Yes. One pair is generated per day and shared by every player.
Related reading & games
- Musical intervals explained and the interval ear-training guide: the gap you are halving.
- Hearspan reproduces an interval from a new tone; Hearkle matches a single pitch.
- Frequency in hertz, for what the number beside the slider means.
Source: McDermott, J. H., Keebler, M. V., Micheyl, C. and Oxenham, A. J. (2010), Musical intervals and relative pitch: frequency resolution, not interval resolution, is special, Journal of the Acoustical Society of America 128(4), 1943-1951.
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