A nasty trick on musicians.
Homage to Larson . . .
Diplacusis, also known as disharmonica or interaural pitch difference (IPD), is a hearing disorder whereby a single auditory stimulus is perceived as different pitches between the ears. Sufferers may experience the effect permanently, or it may resolve on its own. Diplacusis can be particularly disruptive to individuals working within fields requiring acute audition, such as musicians, sound engineers or performing artists.
Actual experience - just as the brain's plasticity starts to "accept" the pitch discrepancies and begins to perceive sound as less distorted, the pitch skew changes/morphs/migrates and sounds uncomfortably distorted anew. In this case, this was accompanied by an increasingly expanding array of tinnitus sounds (proverbial whistling/squealing, aviary/crickets, steady pitches/clusters (cf. pipe organ mixture ranks), notch-filtered white noise) all on top of the chronic (forever) high-pitch cluster (8K-10K).
Some pitches present as multiple pitches as if a harmonic-rich/complex sound (sometimes including a faint original pitch, many times not).
Some research studies focus on the frequency range where the slope of the ear's audiogram results is steeper at the hearing loss frequency. However in the above experience, the perceived pitch shift was across the spectrum (and shifted as time progressed).
One wonders if diplacusis is why some people cannot "match pitch" (how to know which ear is "correct"?!) or maybe having the condition stimulated some composers to write in two keys at once.
PDF blank chart to record pitch skew
(the green "units" on the vertial axis are half steps starting a low CC, such that the data can be quantized in excel or a database for tracking changes over time)
. . . and assuming the subject is a musician or understands pitches.
Prepare an audio patch cable that has an inline momentary switch to select which ear receives a (common) pitch played on a keyboard (synthesizer).
We've found that a pure tone (bass flute or organ flute) patch works best since any overtones/partials can confuse the pitch perception.
Go thru a range of pitches (every fifth or third) and for each test pitch -- present to the bad ear first (so there will be minimal biasing for what the actual pitch is), and then to the good ear.
This depends on the musical training of the subject to discern the relative pitch perceived in the bad ear.
Amplitude has not yet been considered, altho loudness seems to influence the perceived pitch (seemingly not akin to the psycho-acoustic perception effect that louder pitches sometimes seem slightly sharp/JND).
Sometimes the bad ear perception even for a single pitch is so distorted it is perceived as a complex tone with enharmonic partials. No convention has yet been devised to notate the various partials other than a stemmed chord notation to notate all partials perceived..
The data form has evolved over the years to facilitate ease of data capture and detail needed.
Apparatus for presenting a single pitch to each ear, in turn:
Only one channel of the keyboard output is used. That one channel is then steered (switched) to either the left or right ear. The switch's normal position plays the pitch to the bad ear. Pressing the momentary button then switches ear for comparison.
Schematic for above patchcord/rockerswitch: (stereo common/shield is passed through)
