Diplacusis: when the same note sounds different in each ear

What is diplacusis?

Diplacusis (dip-luh-KOO-sis) means hearing one sound at two different pitches. It comes in two forms:

• Binaural diplacusis, the common one: the same tone sounds like a different pitch in your left ear than in your right. Play a note to one ear, then the other, and they don't match.
• Monaural diplacusis: a single tone, heard in one ear, sounds like two pitches at once, or rough and buzzy.

Some hearing-clinic websites say "monaural" means hearing loss in one ear and "binaural" in both. That's a mix-up: the words describe how the pitch is heard, not which ears have hearing loss. This site is mostly about binaural diplacusis.

What does it sound like?

Diplacusis is often much more obvious with music than with speech, because music depends on exact pitch. People describe it as:

• music sounding out of tune or sour, as if the band were slightly detuned
• a chorus or doubled sound, like two instruments playing almost the same note
• a singer who seems flat or sharp, even on a recording you know is in tune
• held notes, such as a piano chord or a sustained vocal, that wobble or clash
• one ear that seems to hear everything a little higher than the other

When both ears hear the same sound, the brain has to combine two slightly different pitches. Sometimes it merges them into one; sometimes you hear the clash. In one study, people with hearing loss merged tones from the two ears that were far further apart in pitch than people with normal hearing did: on average about 1.7 octaves, against 0.17 octaves. That may be why the effect can come and go, and why it's often easiest to notice by covering one ear, or with earphones.

How big is the difference?

Pitch differences are measured in cents: 100 cents make one semitone, the step between two neighboring piano keys, and 1,200 cents make an octave. Trained listeners with normal hearing can tell apart tones only a few cents apart, and untrained listeners need more. Small differences between the ears are normal, and repeated matches vary by several cents even in healthy hearing, which is why a single reading means little.

Diplacusis ranges from subtle to large. In a 2016 study of 43 adults with hearing loss, about two thirds had a clear pitch difference between their ears at the edge of their hearing loss, and about half had a difference bigger than any normal-hearing listener in the study showed: more than about a semitone. The worse-hearing ear usually heard the higher pitch.

What causes it?

Your inner ear (the cochlea) sorts sound by pitch: each frequency makes a particular spot along it vibrate most, and the brain reads pitch partly from where that happens. When the inner ear is damaged or swollen with fluid, that map can shift, so the same note excites a slightly different spot and sounds like a different pitch. If only one ear is affected, the two ears disagree.

Diplacusis has been documented with:

• Inner-ear (sensorineural) hearing loss, especially when one ear is worse than the other. Pitch in damaged ears can also shift with loudness more than normal.
• Ménière's disease, an inner-ear disorder with vertigo, hearing loss, tinnitus and a full feeling in the ear, usually in one ear. Researchers estimate at least half of people with Ménière's have diplacusis, linked to fluid build-up in the inner ear (endolymphatic hydrops).
• Sudden sensorineural hearing loss, where hearing drops in one ear over hours or days. Diplacusis has been measured during an episode and seen to settle as the hearing recovered. More on pitch after sudden hearing loss.
• Noise exposure and professional music-making. Two studies of professional musicians found diplacusis in about 6% of the 380 players assessed. Diplacusis for musicians.

Other conditions that cause hearing loss in one ear, such as a vestibular schwannoma (acoustic neuroma, a benign growth on the hearing and balance nerve), are worth a doctor ruling out, because one-sided hearing changes are a reason to be checked. Diplacusis itself doesn't tell you the cause.

How is diplacusis measured?

A standard hearing test (an audiogram) measures how quiet a sound you can hear at each frequency. It doesn't measure what pitch you hear, so a normal-looking audiogram doesn't rule out diplacusis.

Diplacusis is measured by pitch matching: a tone plays in one ear, then a tone in the other, and you adjust the second until the two sound like the same pitch. The difference between where you set it and where it should be, in cents, is your pitch mismatch. Good measurements:

• play the ears one after the other, never together, so the brain can't merge the tones
• match loudness first, because pitch shifts with loudness, especially in affected ears
• test several frequencies, since the mismatch is often largest in one range
• repeat each match, to separate a real difference from ordinary variation

You can get a rough first reading with our free online pitch check. The Harmonic Recovery app does the full version: a setup for your headphones, a loudness match, six frequencies with repeats, and a chart over time.

When should I see a doctor?

Always get new pitch changes checked, especially if they come with hearing loss, ringing, a blocked or full feeling, or dizziness. Get urgent help for:

• sudden hearing loss in one or both ears, over hours or a few days
• hearing that has got worse over days or weeks
• hearing loss with earache or discharge
• hearing loss with a drooping face, numbness or other stroke-like signs (go to an emergency department)

An ENT (ear, nose and throat) doctor or an audiologist can test your hearing, look for the cause, and treat what's treatable. With sudden hearing loss, time matters: steroid treatment works best when it starts early, ideally within two weeks.

Does diplacusis go away?

Sometimes. When the hearing loss behind it recovers, as it can after sudden hearing loss, the diplacusis can settle too. Researchers also expect the brain to adapt to a lasting mismatch over time, and people with cochlear implants show that adult pitch perception can shift toward the other ear. But there are no large studies of how diplacusis changes over time. Read more about whether diplacusis goes away.

Is there a treatment?

There's no proven treatment for diplacusis itself. What doctors treat is the cause: for example, sudden hearing loss is treated with steroids, and Ménière's disease with diet changes, medicines and other measures. Treating the cause can reduce the diplacusis.

Harmonic Recovery is a practice and measurement tool built on a simple idea: let the ear that hears correctly act as a reference while you listen to music. It is not a treatment, and no study has tested whether this kind of practice reduces diplacusis. What it does do is measure your mismatch the same way each time, so you can see for yourself whether it's changing. Read about the research behind it.

Living with diplacusis

• Protect your hearing. Keep music at moderate volume and use hearing protection around loud noise, so your hearing doesn't get worse.
• Keep a record. Diplacusis can fluctuate, especially with Ménière's. Notes on how music sounds each day, and measurements made the same way each time, make it easier to see a trend and to describe it to your doctor.
• You're not imagining it. Many people spend a long time before they learn the word for what they hear. It's a real, measurable difference in how the two ears hear pitch.