by Neil Bauman, Ph.D.
A musician explained,
I suddenly began experiencing a strange phenomenon with my hearing. I now hear music through my right ear at the correct pitch, while, at the same time, I hear the same music a semitone higher in my left ear. This is frustrating and scary. I can no longer perform my music. A major part of my life has suddenly been snatched from me. Have you ever heard of this before? Am I going crazy? What can I do to correct this condition?
Another person related,
I’ve suddenly begun to experience a rather disturbing auditory phenomenon. Sounds as heard by my right ear are pitched a bit lower than the same sounds as heard by my left ear. This gives music a very frightening and eerie chorus effect that is becoming more and more disconcerting. What causes it? Does it ever go away?
In a previous eZine, I wrote about people who hear music off-pitch—either certain notes, or all notes. (See “When You Hear Music in the Wrong Key” including all the comments.) In most cases, these people heard the same music off-pitch with both ears. This alone was disconcerting and destroyed their enjoyment of music.
However, it is even more frustrating when you hear the same notes at different pitches in each ear and you don’t know which ear to believe. For example, your left ear may hear a note as F while your right ear may hear the same note as F# (F sharp).
Rest assured, when this happens you are not going crazy, but something definitely has messed up the pitch perception between your ears. This condition is known as diplacusis (dip-lah-KOO-sis).
What is Diplacusis?
Diplacusis is a disconcerting condition, especially for musicians, because you hear the same note at two different pitches—often at the correct pitch in one ear and either higher (sharp) or lower (flat) in the other ear. This makes playing, singing or listening to music sound sour (sharp or flat depending on the direction of the frequency-shift). This can be devastating to a musician who has previously had perfect pitch.
The dictionary defines diplacusis as “abnormal perception of sound either in time or in pitch, such that one sound is heard as two. This fancy name comes from two Greek words “diplous”—double, and “akousis”—hearing. Thus, diplacusis is really double hearing or hearing double. (1)
Diplacusis occurs when your ears have a significant difference in frequency selectivity. This results in clashing interpretations (dissonance) of the tones you hear.
Fortunately, although many people hear tones at different pitches in each of their ears, this difference is normally slight. In fact, when the difference in pitch is less than about one semitone (halftone), the average person typically does not notice it. This difference in pitch normally escapes our notice because the slightly different pitches of sound from our two ears merge in our conscious perception such that we only hear one pitch of sound. (2)
Musicians, however, because of their musical training, may be considerably more sensitive to these slight pitch differences. As a result, they may be aware of, and bothered by, smaller pitch differences than even a semi-tone.
Kinds of Diplacusis
Diplacusis or “double hearing” comes in various “flavors”.
Diplacusis binauralis (by-nar-RAL-is) is where you hear the same sound differently in each of your ears. For example, you may hear a different pitch of sound in each ear, or the timing may be different in each ear.
A subset of diplacusis binauralis is diplacusis dysharmonica (dis-har-MON-ih-ka) where only the pitch is different in each ear. Some authorities use the term “Interaural Pitch Difference” (IPD) rather than diplacusis, but they both refer to the same condition. (2)
Diplacusis echoica (eh-KOE-ih-ka), as it’s name implies, is where you hear the same sound repeated in the affected ear—thus you hear the original sound followed by an “echo” of the original sound.
Finally, there is diplacusis monauralis (moh-nar-RAL-is). This is where you hear a single sound as two different sounds in the same ear. (1)
In my experience, by far the most common “flavor” of diplacusis is diplacusis dysharmonica. This is the annoying condition that numbers of musicians experience and the “kind” of diplacusis we will discuss here.
What Causes Diplacusis?
Diplacusis involves a shift of pitch perception. This can happen when the hearing in one ear is damaged (unilateral hearing loss), or the hearing in one ear is damaged more than it is in the other ear (asymmetrical hearing loss). However, the degree of pitch distortion does not appear to bear any simple relationship to the degree of hearing loss. (3)
Incidentally, diplacusis was first observed way back in the 1880s in people with unilateral hearing loss. (2)
If one ear has normal hearing, and the other one has sensorineural hearing loss, you can have a lot of diplacusis. Bilateral sensorineural hearing loss results in less diplacusis but there are probably pitch distortions because both ears are likely messed up in the same way. (4)
In fact, there is a high degree of correlation between the occurrence of diplacusis and damage to the inner ear. (2) Diplacusis is typically experienced as a result of sensorineural hearing loss. Onset is usually spontaneous and can occur at the time of an acoustic trauma or in the midst of an ear infection. Sufferers may experience the effect permanently, or it may go away on its own. (4)
For people who have some degree of sensorineural (inner ear) hearing loss, here is a detailed account of how diplacusis may develop…. (Read the rest of this article here.)