Otoacoustic Emissions (OAEs)

Releated Pieces: Cuboid Nothingness__-- | __-- (b)If; slowly |Static (i&ii) Cycle Forms & Perspectives

Otoacoustic emissions are physiological effects produced by part of the inner ear called the cochlea. According to the ninth edition of the Concise Medical Dictionary, they are defined as:

 

tiny sounds that emerge from the inner ear either spontaneously (spontaneous otoacoustic emissions, SOAE) or shortly after the ear is exposed to an external sound (evoked otoacoustic emissions, EOAE) [...] using a click stimulus (transient otoacoustic emissions, TOAE) or two separate tones (distortion product otoacoustic emissions, DPOAE).  (Martin 2015)

 

My research is concerned only with Distortion Product Otoacoustic Emissions. DPOAEs are also sometimes called Tartini tones, named after violinist and educator Guiseppe Tartini, who is accredited with their early discovery. Tartini discovered, when performing a double stop trill on the violin (the manoeuvre of playing two notes simultaneously), that he could hear a third note accompanying the two he was playing. He came to the conclusion that it was his ears creating the third tone and so began using this technique as a method of creating the impression of more sounds originating from the violin (Hall III & Dhar, 2009, p. 2). A composition of his which features many double stop trills is the 'Violin Sonata in G minor', also known as the 'Devils Trills Sonata'.  

This phenomenon was later studied by psychoacousticians and physicists. Gerhard Vieth, a German physicist, coined the phrase ‘combination tones’ in 1805, which became the standard umbrella term for describing the effect (Hall III & Dhar, 2009, p. 2). 

 

The two main theories in this period were that the extra sounds were originating from the instrument itself and the movement of the air created or they were a figment of the listener's imagination. In, 1856, another German physicist, Hermann von Helmholtz, replied to these theories by proposing, in his article Ueber Combinationstöne, that the extra sounds were originating from within the middle ear and were objective (Kursell 2015). 

There are two recognised subsets of the combination tone: 'difference tones', a frequency at the difference between two original frequencies played, and 'summation tones', a frequency at the sum of the two original frequencies played. Difference tones are the most commonly heard tones due to them being lower frequencies which are easier to hear. There are also masking effects which occur in summation tones making them difficult to recognise (Randel 2003).​

 

Below is an example of how difference tones work. The first two sound files are single static sine tones. The third file is the two sounds played together and the final sound file is the difference tone that one should have heard in the third file.

1400Hz - Sine Wave
00:00 / 00:00
1000 Hz - Sine Wave
00:00 / 00:00
1000Hz + 1400Hz - Sine Wave
00:00 / 00:00
400Hz - Sine Wave
00:00 / 00:00

f1 - 1000Hz. 

f2 - 1400hz. 

f1 and f2 played together to create a difference tone of 400hz

f1 - f2 = f3

1400 - 1000 = 400

f3 - 400hz

f1 - 1000Hz. 

f2 - 1400hz. 

f1 and f2 played together to create a difference tone of 400hz

f1 - f2 = f3

1400 - 1000 = 400

f3 - 400hz

Please note: the sound pressue needs to be significant for the effect to take place so it might require higher volumes than a normal listening situation

In 1978, British Physicist David Kemp carried out the ground-breaking experiment in which he placed a microphone inside his ear and was able to create the first recording of the cochlea-created sounds (Kemp 1978). Kemp coined the term otoacoustic emissions for the phenomenon. It is now standard practice to check for the presence of otoacoustic emissions in hearing tests on newborns and infants. The existence of the cochlea response is a sign of a healthy and correctly functioning hearing system (Kemp 2002). 

Returning to the musical or artistic applications of Distortion Production Otoacoustic Emissions, although a vast amount of sound work may feature the effect as a byproduct of the composition, very few composers and artists have explicitly intended to use the feature. However, Maryanne Amacher is an artist who aimed explicitly to achieve this effect by wanting to ‘release this music which is produced by the listener’ (as cited in Ouzounian 2008). She describes her use and the experienced gained from DPOAEs on the album liner notes of her 1999 release Sound Characters (Making of the Third Ear),

 

‘When played at the right sound level, which is quite high and exciting, the tones in this music will cause your ears to act as neurophonic instruments that emit sounds that will seem to be issuing directly from your head ... [my audiences] discover they are producing a tonal dimension of the music which interacts melodically, rhythmically, and spatially with the tones in the room. Tones “dance” in the immediate space of their body, around them like a sonic wrap, cascade inside ears, and out to space in front of their eyes ... Do not be alarmed! Your ears are not behaving strange or being damaged! ... These virtual tones are a natural and very real physical aspect of auditory perception, similar to the fusing of two images resulting in a third three dimensional image in binocular perception ... I want to release this music which is produced by the listener …' (Amacher 1999).

 

Her pieces Head Rhythm 1 and Plaything and Synaptic Island both involve sections where the only sounds heard are layered rhythms of pure tones. The listener’s ear reacts to these sounds by presenting the DPOAEs which add another layer of poly-rhythmic material which is not present in the original work. Another work from the 1999 album is Chorale 1, which slowly evolves the texture of the emission through changing to a closer frequency relationship between the sounds used affecting the beating created (Kirk 2010).

Maryanne Amacher- Head Rhythm 1 and Plaything 2 (1999)

Jacob Kirkegaard created a work in 2007 called Labyrinthitis in which he directly played with the cochlea phenomenon. Kirkegaard used an anechoic chamber to record the response from his own cochleas when being presented with the pure tone stimulus. The piece involves the recordings of Kirkegaard’s ear emissions, which in turn also trigger the listener’s distortion product response. Douglas Kahn, the author of an essay which accompanies the release of Labyrinthitis stated, ‘Kirkegaard has countered Duchamp’s dictum, “One can look at seeing, one can’t hear hearing.’ (Kahn 2008). Using recordings of inner ear emissions has been a continuing theme running through Kirkegaard’s work. In 2016, during a residency at St. John's College at University of Oxford, the artist recorded the spontaneous otoacoustic emissions of staff and students at the university. These recordings have led to two pieces including, STEREOCILIA - for 7 Ears and EUSTACHIA - for 20 Voices. Stereocilia is a work which uses the recordings of the staff and students and explores the ‘single or clusters of tones, that some ears emit without stimulus’ in a compositional context (Kirkegaard nd). Eustachia uses this material as a corpus to compose a piece for twenty voices. The programme note on Kirkegaard’s website states:

‘These recorded 'ear chords' were filtered, analyzed, and then interpreted for voices. The work connects two intimate organs of our body: the ear and the throat. The ears are the composers, the throat and mouth are the performers.’ (Kirkegaard nd)

In my works, I intuitively ‘tune’ the frequencies to create the most intense physical effect I can with a disregard for the musical interval or notes achieved in the process. As a starting point, I use a ratio of 1.2 which creates a Cubic Difference Tone (CDT).

 

The CDT is most clearly audible when the ratio of the acoustic signals, f2/ f1, lies between 1.1 and 1.25. Ratios within this range coincide with musical intervals between a major second and a major third. And, as we expect with musical intervals, ratios below 1.14 produce auditory roughness (or dissonance from the musical perspective). (Kendall & Haworth & Cadiz, 2014) 

 

Below is a basic demonstration of how I approach otoacoustic emissions in my work.

[Video needs to be re-done with more information] 

 

References 

 

Hall III , J.W. & Dhar, S. (2009). Otoacoustic Emmissions: Principles, Procedures and Protocols. San Diego, CA: Plural Publishing.

Kendall, G.S., Haworth, C., & Cadiz, R.F. (2014). Sound Synthesis with Auditory Distortion Products. Computer Music Journal. 38 (4), 5-23.​

Kemp, D. (2002). Otoacoustic emissions, their origin in cochlear function, and use. British Medical Bulletin, 63 (1), 223-241. doi: 10.1093/bmb/63.1.223.

Kemp, D. (1978). Stimulated acoustic emissions from within the human auditory system. The Journal of the Acoustical Society of America, 64 (5), 1386-1391. doi: 10.1121/1.382104.

 

Kirkegaard, J. (nd). EUSTACHIA - for 20 Voices. Retrieved from http://fonik.dk/works/stereocilia7.html.

 

Kirkegaard, J. (nd). STEREOCILIA - for 7 Ears. Retrieved from http://fonik.dk/works/stereocilia7.html.

 

Kirk, J. (2010). Otoacoustic emissions as a compositional tool. In Proceedings of the 2010 International Computer Music Conference. Paper presented at the State University of New York, Stony Brook, New York, 1-5 June. Ann Arbor, MI: University of Michigan.

Kursell, J. (2015). A Third Note: Helmholtz, Palestrina, and the Early History of Musicology. Isis, 106 (2), 353-366. doi: 10.1086/682003.

 

Lohri, A., Carral, S., & Chatziioannou, V. (2012). Combination Tones in Violins. Archives of Acoustics, 36 (4), 727-740. doi: 10.2478/v10168-011-0049-1.

Martin, E.A. (2015). Concise Medical Dictionary (9th ed.). Oxford: Oxford University Press.

Randel, D.M. (2003). The Harvard Dictionary of Music (4th ed.). Cambridge, MA: Belknap Press of Harvard University Press.