The Perceptual Mechanics of Noise-cancelling Headphones
Photo: Barbara Wendelbo
Stig Hovlandsdal Øvreås
Publisert: 7. august 2019
This manuscript was rejected by the academic journals New Media and Society, Human Technology and Sound Studies over a period of three years. We now publish it on the TekLab website. This is because we believe it may be of interest to the academic field of media technology. Its analysis of noise-cancelling headphones is fundamentally interdisciplinary, as it combines humanist phenomenology with mathematical formulas to pinpoint the mechanics of such headphones. We believe this is the reason why it was rejected, without recourse to revisions and resubmissions. The manuscript was too unusual for all three journals, and they rejected it for approximately the same reasons: They found it too interdisciplinary for the journal, they were unable to find reviewers for it, or the reviewers dared not recommend it due to felt lack of expertise in either one or the other field. None of the reviewers said that the argument was of too poor academic quality.
The Perceptual Mechanics of Noise-cancelling Headphones
Noise-cancelling interfaces make it possible to balance your attention between your surroundings and the music or speech that you want to listen to. In this paper, we discuss attention management as an action possibility of noise-cancelling headphones. This is an inflexible physical functionality. All human experience of a given headset relates to the same physical set-up, with the same physiological and perceptual responses from our bodies. We describe the perceptual mechanics of noise-cancelling headphones with inspiration from J.J. Gibson’s theory of affordances, and we apply the mathematical language to express its order and inflexibility. We report from a field trial with ten experimenters who used noise-cancelling headphones in Central London, recounting their descriptions of physical qualities of noise-cancelling headphones that they enjoyed or disliked. The article also deals with AI-supported noise-cancelling headphones. In the conclusion, we discuss the immersive character of these interfaces, and show how an understanding of their mechanics can be beneficial to storytelling for Augmented Reality (AR) and Virtual Reality (VR).
Keywords: noise-cancelling headphones; perception; attention; artificial intelligence; sound; field trial.
Noise-cancelling headphones are widely used among people in industrialized societies in Europe, and globally. City dwellers use them on the plane, train and the bus, as well as in the street. Sony, Bose and Beats are well-known manufacturers of such interfaces. Surrounding the actual use, there is a culture of tastes and opinions about different brands, their pricing and their good and bad sides. Most people have personal experience with different types of headphones, and engage in ad-hoc, heuristic evaluations. We believe there is a need for more formal research on these headphones’ role in everyday life.
Noise-cancelling headphones are more advanced than regular headphones. They are meant to filter the sounds of the surroundings, quieting and harmonizing the soundscape for some human purpose, enabling us to focus attention to preferred cultural sounds. Their use value seems straightforward: In many surroundings, noise is experienced as a practical problem, and noise-cancelling technology is an advanced mechanism with which to remove the noise . However, already there is room for misunderstandings. While information theorists like Shannon and Weaver (1953) presume that noise is simply disturbances and therefore unwanted, the humanist idea of “noise” also includes loud rock bands, screeching wheels, and alarms that can in various ways give pleasure. Attali (1985: 3) celebrates the cultural complexity of noise, and this sentiment is familiar in humanist sound studies. Our study starts from Shannon and Weaver’s negative definition of noise. This is an information theoretical perspective where noise is dealt with technologically as something disturbing that should be identified physically and cancelled out from the headphone listener’s experience.
There is social criticism of headphones and the modern consumer society. Hagood (2011) discusses how listeners create a soundscape for suppressing the presences of others with the help of noise-cancelling headphones. Other researchers have also documented the individualistic character of headphone listening. Simun (2009: 922) shows how people in London use the mp3-player to shape their environment, and build a protective shield around them. Burns and Sawyer (2010: 97) show that people use the portable music player as a defence mechanism against encounters with other people. Bull (2007: 5) reminds us that the experience of the solitary individual is wanted, and considered pleasurable or positive. Bull (2007: 5) writes, “The desire for solitude in the automobile is mirrored in the desire for solitude in the street and the home as many retreat into the most private spaces of their already privatized home”. A stronger political criticism comes from Groening (2010: 1331), who argues, “the contrary impulses of moving through the world while retreating from it” are produced by the economic and social structures of corporate media.
Jones and Schoerkmaier (2012) discuss how improving noise-cancelling headphones can be beneficial to amend hearing losses. Liang et al. (2012) found that noise cancelling reduces people’s preferred loudness level for music. Especially in urban environments, people’s preferred listening loudness level gets so high it can be considered a health risk (Wash 2013). There are experimental studies of the potential benefits of noise-cancelling headphones for medical purposes. No effect was found as a pain relief during prostate biopsy (Tsivian et.al. 2012), but a good effect was found for performance within an aviation environment. “Performance when using noise-cancelling headphones was significantly better in both the single-task and dual-task condition compared to using no headphones […] These results highlight the benefits of noise-cancelling technology in an aviation setting.” (Molesworth et.al. 2013). Keep in mind that the present article is oriented to another noisy environment, namely Central London, UK.
The last research topic we want to mention in this context is immersive media. This is a term for computer interfaces that surround the user completely with mediated sound and vision. In research, it is mostly referred to as augmented reality (AR) and virtual reality (VR). Azuma (1997) and Azuma et al. (2001) define AR as superimposing artificial objects onto the real world. With the aid of a technology, a user senses the artificial object as an integrated part of the perceptual situation. Härmä et al. (2004) use the term augmented audio reality for hardware technology and solutions that apply to the auditory aspect of perception.
The theory of perceptual mechanics
The research question for this study is different from those reviewed above. We want to describe as precisely as possible, how this interface mediates the world for the user; specifically how it influences the user’s attention to their surroundings.
We start from the theory of affordances emerging from the works of the psychologist J.J. Gibson. It has proved a fruitful way of understanding technology; it can be seen as a materialist alternative to the social constructivist tradition. It helps us to frame the mechanics of noise-cancelling interfaces. According to Gibson, “the affordances of the environment is what it offers the animal, what it provides or furnishes, either for good or ill. It implies the complementarity of the animal and the environment” (Gibson 2014: 127). For example, a ledge affords sitting, air affords breathing and water affords drinking and bathing. Thus, affordances refer to the practical meanings that objects have for observers, and these meanings remain invariant in most cases (Goldstein 1981: 192). Design theorist Donald Norman has a similar explanation: “The term affordance refers to the perceived and actual properties of the thing, primarily those fundamental properties that determine just how the thing could possibly be used”, (Norman 1988: 9).
Gibson points out that affordances can be considered action possibilities for humans. Affordances are objectively measurable, and independent of a person’s ability to recognize them. Their usefulness depends on the ability of a human to exploit their action possibilities. For example, a person’s reaction to a flight of stairs is basically, “here is a way to go up” and not “here is a series of flat, layered surfaces” (Goldstein 1981: 192). Notice that it is the material limitations of objects that create these action possibilities. If all objects could flexibly alter their appearance at any time, alternating between being hard and soft, small and large, loud and quiet, stinky and pleasing, there would be no action possibilities.
Our study is chiefly concerned with paying attention to the surroundings. It is important to note that in the humans’ explorative projects, the surroundings are always a significant factor. Perception is an active search for information about the environment, where the individuals apply their bodily skills and explorative strategies toward the object in question (Merleau-Ponty 1945). Gibson intimates that the human body functions by constantly evaluating the “… –bility” of things, for example the climbability of a rocky path, the drinkability of watery fluids, the readability of a text and, in general terms, the usability of anything that might serve useful. In phenomenology, the human tendency for assessing possibilities for practical engagement is important, and we consider this to be a form of attention.
"To understand the cancellation process, we start from the fact that sound is waves. Waves in a physical medium like air or water have the property that they are additive in their amplitude, so if you add a wave with a negative amplitude to a wave with same positive amplitude, both waves disappear. This principle is applied in noise-cancelling headphones."
- Lars Nyre and Bjørnar Tessem
Noise cancelling as perceptual mechanics
We want to give a precise description of how noise-cancelling headphones work, and we call this the “mechanics” of the tool. In our conceptual framework, this is the same as defining its functionality or its affordance, and we adhere to traditional conception of mechanics as the sciences that describe the behaviour of physical bodies when subjected to forces or displacements, in our context the most important are solid mechanics (streets, vehicles, etc.) and acoustics. A basic pair of noise-cancelling headphones have two solutions for removing ambient noise from the ears of the users. For lower frequencies, silencing is effectuated by creating sounds that destructively cancel out the ambient sounds, and for higher frequencies, it is done with soundproofing or padding to shut out the ambient sound.
To understand the cancellation process, we start from the fact that sound is waves. Waves in a physical medium like air or water have the property that they are additive in their amplitude, so if you add a wave with a negative amplitude to a wave with same positive amplitude, both waves disappear. This principle is applied in noise-cancelling headphones. A microphone in the gear collects the sound waves (or in fact the total sound impression which is the sum of all sound waves) from the surroundings; then electronics in the headset generates a sound with exactly the opposite amplitude to the external sound slipping through the padding.
The result is that the generated sound actually cancels the ambient noise, and what remains to be heard is the music or radio program. However, wave physics limits what the technology can do. Higher frequency noises are harder to cancel out for the human ear. The noise-cancelling effect is mainly effective for long wave sounds (100 Hz corresponds to 3.4 m wavelength). Even if the cancellation wave is a little out of sync, the effect will still be there. However, for short wave sounds (10000 Hz corresponds to about 3.4 cm wavelength) there is a problem. Small variations in the actual distance between the loudspeaker in the headphone and the eardrum will have a significant effect on noise-cancelling efficiency. If you increase or decrease it a centimetre, the generated cancellation sound will not hit the eardrum in perfect sync with the ambient sound, and instead of noise cancelling, you may have noise amplification. Therefore, active sound cancelling is not practical with today’s technology for frequencies above 1000 Hz. Sound cancelling at higher frequencies is still only done through other soundproofing technology like padding.
To further explore the human experience of the noise-cancelling affordance, we relate to the phenomenologist Ihde (1997: 52), who analyses perceptual attention with a focus on the auditory dimension. Ihde argues that humans experience the world by encountering different entities. Stable entities (X-entities) are present only to the eye, like the sidewalks and walls along the street. These are not heard at all. The human will also experience moving entities (Y-entities) that are present to both the eye and the ear, like buses and cars passing in the street, and people walking and talking. Ihde argues that there are also events that make sounds without having a visible presence (Z-events). His main examples are wind blowing around a corner, or an air conditioner making low-frequency noise.
The mechanics in mathematical terms
We adapt Ihde’s ideas to our purposes, starting with “all of perception” – an entity consisting of anything in the world that can be experienced by a human with some level of attention. That is, things perceived with all or some senses; seen, heard, and tactile. Examples are a bus driving along the street, and humans talking to each other. These we call P-entities (all perceived entities). P-entities have two subsets that are of particular interest in an auditory context:
(1) Auditory entities (A-entities); entities perceived through the ears, often with other senses as well. Cars, talking people. These include both Y-entities and Z-events in Ihde’s vocabulary.
(2) Non-auditory entities (An-entities); entities perceived not through the ears, but with a subset of the other senses. Traffic lights, street signs, walls along the pavement. These can be seen as equivalent to Ihde’s X-entities.
In addition, we introduce a third set of perceptual entities:
(3) Mediated auditory entities (Am-entities); entities chosen for listening through the headphones. Recorded music, podcasts, recorded bird song. Ihde does not have these types of entities in his vocabulary.
We will now present the functionality of noise cancelling in a mathematical form. P can be seen as the union of auditory and non-auditory entities, i.e., The noise-cancelling affordance can be seen as a function c, which cancels all sound (disregarding the imperfection of the technology) and leaves us with an additional set of non-auditory entities, c(A). In addition, the headphones add mediated auditory entities Am. The result is a set of perceived entities that consist of the original non-auditory entities An, the transformed auditory entities c(A), and the mediated sounds, Am.
Thus, the typical use of headphones not only affords noise cancellation but also enables the user to change the attention from noise in the environment to preferred sounds being projected inside the headset. They are unavailable for everybody but this individual user, and can for example consist of jazz, hip-hop, a film podcast, a news bulletin or any other genre of sound content. The sounds were originally produced somewhere else (e.g. in a recording studio), and they now appear in the headphones regardless of where the person is. Suddenly the user has a device that not only facilitates reduction of noise, but also enables the user to consciously control what perceptual content deserves their attention. In the following two-part analysis, we will discuss how the interface was experienced by ten Londoners in a field study.
Analysis 1: Describing the new perception
The researchers conducted a field trial in Central London in 2013 with ten informants. All the informants have been given pseudonyms instead of their real names. They were asked to test a new line of noise-cancelling headphones: the Bose Quietcomfort 15. We had three sets and the informants took turns testing them. The concept of a “field trial” is often used in information science to describe studies where informants try a technology and report on their experience of using it (Rodgers, Sharp & Preece 2011). It is a task-driven approach, where the task is performed due to an incentive, and the researcher is monitoring the experience and reflections relating to the task.
The purpose of such studies is often to assess the efficiency and effectiveness of a product— often in order to improve it. An example of such a study relating to noise-cancelling headphones is Guldenshuh et al. (2012), who show us how user assessments can be used as an alternative to ear simulators in assessing quality of noise-cancelling headphones. Fincham, McGuinness & Murray (2010) give a good presentation of methods for studying people on the move, whether in cars, on public transport or for sporting purposes.
For the present field trial, we curated 3 x 45 minutes of mediated sound in the genres of music, live news and podcast lectures, and we asked the informants to listen outdoors and/or in transit. All the informants live in Central London, are adults and own an iPhone. The youngest is 27 years, and there are no children, teenagers or students. The oldest is 50 years old, and there are no grandparents or pensioners. They are all working adults with good reason to travel across the city; some every day, and others a few days a week. They all listened to the selected sound content in the streets, on the bus, and in the Underground, and some of them also while jogging, driving a motorcycle or riding a bike. Informants wore their personal iPhone 5s and a pair of Bose QuietComfort 15 noise-cancelling headphones supplied by the researchers.
After three to eight days, the research team talked with the informants about their headphone experience during a one-hour interview. This procedure is related to ethnography and audience studies, where in-depth dialogue with a few people is preferred (Bull 2000, Behrendt 2012). Through the hermeneutical analysis described above, we came up with three sets of observations that indicate the mechanics of the technology, and its influence on the attention management the users are engaged in. These are noise-cancellation and listening to mediated sounds, imperfection in noise-cancellation and its consequences, and finally, requirements from the surroundings.
Noise cancelling and listening to mediated sound
All informants were used to listening to music, etc. while moving around the city, and could easily compare the noise-cancelling headsets with their regular gear. The overall impression is that the noise-cancelling sets felt like a luxury, with higher qualities than their own relatively cheap and disposable earbuds and headphones. Normal headphones are, as noise-cancelling headphones, supposed to provide Am-entities of the user’s own choice. Here we discuss how c(A), the noise-cancelling function, changes the users experience of the mediated sounds as compared to ordinary headphones.
Quality of sound reproduction. This is the main traditional quality measure, and it refers to the technical quality of the mediation of Am-entities; of the bass, the high tones and other aspects of the audio as contained in the mp3 file, live transmission, etc. This comparison by William (36) is to the point: “I don’t know if it was side-chain compression or something, but the music was quite sort of pumping. Yeah, I didn’t feel it was quite as dynamic as when normally I’d listen to it on my Sennheisers. I don’t know if that’s the processing or something that’s going on?”. The respondents were overall impressed with the sound quality. Agnes (50) says: “I thought the music sounded really, really good on them”. John (38) says: “It was almost too perfect. It took me a while actually to listen to the programme, or the subject, rather than listening out for why this sounds so different”. Diana (47) says, “This sound is highly superior”. Agnes (50) liked the acoustic representation. «I felt a three-dimensional effect of the sound, and they really make me feel like I’m in the room».
Most of the quotes regarding sound quality deal with the experience of music in particular. Some described it as very good. Richard (47): “When you actually play the music; beautiful quality. Beautiful quality!” John (38): “With these, it made a hell of a difference, man. It was very good quality and really sort of crisp” Isaac (41): “I was listening to like Hendrix and stuff that was recorded in the 60s, and it still sounds great to me”. William (36): “The Fugees song was very impressive because the intro has a lot of quiet noise in it. And it kept on sounding quite good because of the noise cancelling”.
Effectiveness of noise reduction. It was clear that informants enjoyed the reproduction quality of music and talk. The novelty is that these headphones are supposed to isolate much better than regular headphones, and thereby create a more silent listening situation. There is a good description from John about how A-entities are changed by the c(A) function: «Just now there was a group of kids in my carriage on the Tube, and they were rapping and stuff. It was quite amusing; they were well behaved and stuff. But when I put the headset on, I felt completely removed from it. I could still see their mouths going, but it does separate you out. It was quite nice, actually.» John (38) again: «I had the Bose on listening to my own stuff. With the old-style headphones the traffic would definitely drown out the music, however loud you had it, and especially when it’s going right past. With the Bose, you can still hear the traffic when it’s close up, but it’s not so “vroom!” in your face. It’s muffled, a littler noise». For most of the respondents, it was positive to not hearing sounds from the surroundings. Agnes (50) says, “in some areas I couldn’t hear anything. And it was just fantastic.” Laura (27) says, “if you’ve got music with a beat and a good sort of rhythm, you couldn’t hear anything. Which is nice”.
Enjoying content immersion. There is an aesthetic sense of being absorbed into the music. To be isolated from the surroundings was considered a pleasant experience by many. Elisabeth (32) says, “I couldn’t really hear anything going on around me, and so that was quite nice, being in like a bubble.”. And they used several more terms for this experience, like being “cocooned”, “absorbed”, “lost”, “deep into music”. Here is a typical comment from Elisabeth (32), “You feel cocooned by them. Even in body language if you go like that [cradling up her body], you’re in your own world, aren’t you? You’re going away from everybody else.” Diana (47) says, “It just absorbs you in the sound. You’re lost in that moment; you’re lost in that song.” Richard (47) says, “I had that experience where I was deep into beautiful quality music, really relishing it”.
Laura (27) enjoyed the headset’s musical experience very much: «I had to call a friend, but wanted to carry on listening rather than call him. I took them off and went outside and made the call. I was like, holding them and I wanted to have them back on. I was really enjoying the experience.» John (38) was almost religious in his description, «This sounds really daft, but I feel as if I’m in a higher place. Especially on the train, I felt as if I wasn’t involved in all the hustle and bustle. So I felt above everybody, in a way. I was able to get on with stuff in my own world, and not be troubled by a trolley going past or something. It was more peaceful, and almost a bit superior because I know that I’m in a space that’s nicer than everyone else’s. In my head, sort of.»
Healthiness. Noise protection comes across as a healthy way of listening. Richard (47): “I’m paranoid about listening to stuff too loud. With a normal pair of headphones, you’re picking up quite a lot of sound, but with these you can listen at quite a manageable level whilst still cancelling the sound out”. John (38) also commented on the aspect of not having to turn up the volume. “It was a heck of a difference, and it felt more healthy to my ears, I suppose. Diana (47) says, “maybe it sounds a bit crazy to say they’re healthier, but …”. It is worthwhile noting that the use of noise cancelling to avoid harmful loud noises from the surroundings was not an issue among the respondents.
The users have positive experiences with noise cancelling in relation to listening. They enjoy it more, are immersed into music, and feel that it is healthier. The combination of c(A), which reduces the unwanted attention to A-entities, and Am-entities creates a different, more valuable experience for the user.
Imperfect sound cancelling
As mentioned in the introduction, noise cancelling does not work well for sound frequencies above 1000 Hz. The users reacted to this imperfection, and felt it was a nuisance.
Leakage. There is a certain leakage of sounds. The tool quiets down everything, but it does not take away all the noise. Agnes (50) says, “I suppose the irritating thing was that I could hear the cars. You know even the swishing of them going by. You know when you’re on the road and the only noise really is the cars and buses. The buses I would maybe slightly expect, but the cars just going by, their engines are quite high. I suppose there are a lot of taxis where I live so that’s to do with diesel, or I don’t know… But, that was slightly disappointing for me.” Other informants complained about the same thing.
Product weaknesses. There were some deficiencies in the functionality. Respondents reacted negatively to a side effect of the technology, where the sounds from their footsteps are amplified in the headphones. Agnes (50) says, “My shoe vibrated up through the sound. And it was much more than when you don’t have anything on your ears. It’s a strange experience, and I don’t think they’ve got that bit sorted out”. In addition, air pressure is amplified instead of silenced. John (38): «On the underground, on the escalators and platforms there was a sort of “khhhhh», like the sound when you’ve got a microphone outside and there’s wind». There is a further complaint from John (38). He thinks it would be most helpful to have a microphone on the cord, like on the iPhone sets. “I would be able to take calls, and it cuts out what you’re listening to». Diana (47) says the same thing, adding that she would not like to be warned by a ringtone, but rather by a vibration.
Leakage and distortion of external sounds, the c(A) function being not perfect, was seen as a weakness by many respondents, contributing to a lesser sense of attention management. This feature of the noise-cancelling headphones should be added into a reformulated mathematical expression. The reformulation may be expressed in a form where c(A) is taken to represent all perfectly noise-cancelled perceptual entities, whereas Ar-entities is a new type of entities representing perceptual entities where their sound expression has been distorted, for instance by sound level reduction or amplification. A reformulated formula describing this is:
Attention requirements from the surroundings
Noise-cancelling headphones would work wonderfully to quiet people down if it were not for all the A-entities in the surroundings that we need to attend to. A large city like London is a probabilistic environment where traffic, movements of people and all kinds of regulations create effects that are unknown until they are encountered. There are dangers and risks, and accidents can happen. We analyse how the combination of c(A)-entities, Ar-entities, and An-entities together (excluding Am-entities) enables the user’s attention management to the surroundings: visual vigilance to compensate for lack of sound cues, being apprehensive of other humans, and relaxation in regulated environments.
Need for some leakage of noise. Many informants saw it as an advantage that the headphones allowed some sound to pass through. Humans need constantly to monitor the surroundings, especially in demanding environments. Agnes (50) says «I think it’s important that you realise you’re outside, or that you have some reference. You are outside in a specifically urban environment, because otherwise you could just go off to Doo La-land, and not know that there’s a car coming. For safety reasons, it’s quite important to have a reminder or reference to events – a slight beep or a change of some kind». There is also important information relating to public transport service, delays, alternate routes, etc. This means that it was sometimes handy to hear announcements, even if they were silenced to a level where one cannot hear the semantic content. Diana (47) says, “for example on the Tube I was listening to Spotify songs, and I could hear there was an announcement. I couldn’t hear anything specific, but I would be able to take them off in case there was something I needed to listen to. So there is just enough leakage”.
The users found the headphones useful for excluding the external environment by removing external sound, thus helping to reduce the importance of other perceptions, so they were able to listen in concentration to their chosen sounds. Still, the users believe that there are things in the environment that need their attention, and the damped sounds helped them be aware of critical traffic information. The imperfect noise cancelling, which left some Ar-entities, was seen as valuable.
Visual vigilance to compensate for lack of sound cues. The surroundings can be dangerous, demanding perceptual attention. Especially when walking in the streets the user must be aware. Informants overall enjoyed the quietness of the headset to the extent that they did not take them off even in demanding situations, and they compensated with increased visual vigilance. Agnes (50): «I’m very visually aware. I pick up body language really quickly, so I would know if something was going on. Wearing the headset wouldn’t interfere with my perception of what was going on.» They trust that their visual perception will compensate for the artificial quietness. Laura (27): «When I’m on the move with my headphones on, I’m definitely looking around a lot more, because you have to be aware. I also listen to music when I’m walking around at night, but I’m always, always aware.» Some informants engage in behaviour that requires extraordinary vigilance. One informant was riding a motorcycle in city traffic wearing headphones, and some respondents also mentioned cycling with headphones. The combination of a modified attention to c(A)-entities and strongly increased attention on An-entities was an observed effect.
Being apprehensive of others. There was a felt need for being socially attuned to the people around you. This was felt particularly strongly by Virginia (29), and we will trace her attitude in some detail. She says, “If somebody was going to say something to me, I’d like to know if they were in the right or in the wrong. I like to be totally aware of my situation. If I’ve done something wrong, fair enough, but I’d like to know it for myself. And having the headset on seems to take that away”. Virginia is constantly aware of potential danger from other people, having experienced how chaotic situations may influence your perception. She says, «I had my bag stolen once. They didn’t actually get it, but this guy came up behind me, hit me on the shoulder, and wrestled for my bag for a good few minutes. And I was on the phone, so I didn’t notice. And with noise-cancelling headphones; could you hear someone coming up behind you? I don’t know, but to take that away from me just seems a bit weird.» Virginia was not comfortable with having only c(A)-entities, Ar-entities, and An-entities to relate to their surroundings, in particular in the context of spoken communication.
Regulated situations allowing for relaxation. Less active surroundings make the listener more at ease than demanding ones, and places like the bus seat are where the informants express greatest pleasure and satisfaction. The noise may be very loud sometimes, like on the Tube during rush hour, but that might not be the most stressful thing. Also, there is a relaxing kind of automated bodily behaviour on the Tube. Catherine (39): «On the Tube, I’ve got to weave through all the different tunnels and make lots of changes, and sometimes I can switch off and be ‘led’. I can be led by directions, I can be led by the Tube system. I don’t have to use my own faculties, as it were. I’ve still got to be aware of my journey, looking out for directions, but I’m being spoon-fed and led on the Tube. It’s easier just to follow the direction, a way of being directed to somewhere.» In Catherine’s perspective, a non-negotiable regulation of movement can be a good thing in the big city.
There is a certain degree of stability and therefore less need for constant attention to the route through the surroundings. There is more room for attention to the cultural sound content in all its richness of meaning and texture when not having to look at things. The underground enables a relaxing mode of listening. The underground is a good place to use noise-cancelling headphones to pacify oneself. Laura (27): «Everyone is so silent and in their own world, especially early in the morning. I would hate to be on the underground and not listen to anything, ‘cause I would probably look around a lot more, you know». In this case, the stability of c(A)- and An-entities enables a higher degree of focus on the Am-entities.
We have seen the array of action possibilities that noise-cancelling headphones can afford humans; like high quality listening, healthy listening, and isolation from a disturbing environment. The transformation of A-entities to non-auditory entities contributes to avoidance of types of sounds considered to be unwanted (exemplified by buskers on the London Underground). At the same time, this transformation enables a full attention on Am-entities in highly regulated environments. Still, we observed that the users considered, to a varying extent, that some A-entities should continue to be A-entities, but perhaps in a different form. The need to use all senses in a complex, chaotic environment is seen to be essential; our attention needs to be at a maximum. The imperfection of noise-cancellation contributes in an unintended manner to maintain some wanted A-entities. This is discussed in the data under the category on attention requirements. Furthermore, much of the findings in the improvement category also relate to how we want to keep important A-entities like ambulances and messages on the tube as A-entities.
"The technology can learn from your behaviour."
- Lars Nyre and Bjørnar Tessem
Analysis 2: Enhanced by Artificial Intelligence
In newer noise-cancelling headphones, we can see the initial inclusion of intelligent noise cancellation and sonification functionality as a modified version of the basic affordance. We suggest a mathematical formulation of the added feature of intelligent situation awareness. First, we define the set of auditory entities that one considers to be of use for a listener in a specific context. We note these entities Aw,s , i.e., the wanted entities in a situation s. The sounds we want to cancel thus become . A new function c with two arguments, both the situation, and the auditory entities, will now consist of two parts. First, the original noise-cancelling affordance c is applied to only. In addition, a function p modifies the wanted sounds to something meaningful and personally acceptable for the listener. Thus, intelligent noise cancellation can be written as a new function:
In the original formula, we can now substitute c(A) with c(s,A) to obtain smart noise-cancelling headphones. Intelligent sound cancellation as formulated here will probably increase the user’s attention control, enabling them to receive needed perception from the surroundings according to own preferences, different from the previous situation where noise slipped through due to technological constraints.
Note that this is not the same as the formula that included Ar-entities. Ar-entities are results of the imperfection of the machine. On the other hand, the users’ appreciation of Ar-entities was helpful in giving us an indication on how to formulate the functionality of the intelligent headphone with perfect noise cancelling.
We have data on this topic from the field trial, too. We asked informants to imagine the future of noise-cancelling headphones and give advice about what designs should be made. The dialogue produced three specific pieces of advice.
Smart noise cancellation. Presuming that the main affordance of the headphones is to make the environment quieter, several informants ask for smart filtering of noise. All sounds from the outside can be analysed to select what should get through and not. Sounds that are probably important for the wearer, like voices directed directly at you, sirens in traffic and traffic approaching from behind, would be filtered in. Isaac (41) imagines intelligent filtering-out: «It would be interesting if they could filter out buskers, – and everyday chat, you know». Elisabeth (32) suggests a function called «Complete Silence». «It would be fantastic never to hear a siren going across the street. That is the most annoying sound ever. The buses, the trains, the trucks braking, all of that. No one wants to hear that. But I think obviously it’s quite important to hear things like “Please mind the gap,” so you don’t kill yourself. I don’t know how they would figure that one out, but …»
Sensors can detect the type of behaviour the user engages in now; e.g. sitting quietly in a bus or running in the park may influence the selection of content to the user. Future technologies will have more finely adjustable cancellation abilities. Laura (27) plays along with this idea: «For cycling, you might want to be a little bit more alert, but when you get to work and have people around you, you just want to block everything out and you could just whack it back up to max».
Sonification of non-auditory entities (both An-entities and c(A)-entities). Another scenario is that the headphones could shut out absolutely everything, yet warn you with a noise or vibration when demanding situations appear. Sonification means that a technological function is accompanied by a sound in order to make it easier for humans to stay in control (Dubus & Bresin, 2013), such as a beep for each product sent through the cash register at a supermarket. An interesting question arose. Would it be better to have another noise, or should it just be the real sound in augmented form? Laura (27): «maybe a slight vibration if there was a siren or danger, or what else could there be? An announcement or something like that». Agnes (50) thinks that such sonification should have the real sound in a quieter version. «Because the sound gives you the quality of what it is: so it’s telling you what it is, rather than having a beeping sound. You would have to invent a different beep for every sound, and I would prefer to have the sound».
Personalized sound content. The technology can learn from your behaviour. Players could be connected to GPS information so that when the user walked in a certain area, certain types of music or news would be launched. Agnes (50) likes this idea. «I’d quite like that, because it takes the work out of having to actually find it. For me it feels like a lot of effort to find good content». William (36) is positive to «Anything that can tailor my experience, or the content I’m receiving has got to be a good thing». «Having headphones that can talk to you while you’re walking through the street. Like, “Oh this is the Ten Bells, this is the pub where Jack the Ripper used to drink.». I think it’d be a useful piece of technology. You could even have adverts from local places ‘round the place: “We do Bagels here” or “We work with people who are homeless.» Here we see that the user is willing to leave the choice of Am-entities to the machine.
Personalization through speech recognition is also an opportunity. Elisabeth (32) does not think the technology is mature yet. «Those programs don’t immediately know your voice and get everything right. You have to train them a little bit, so they get used to your voice. I imagine the headphones would have to get used to your voice». Since the interviews were made, in 2013, there has been great progress when it comes to voice assistants. There now exists voice-guided headphones on the market.
The article has analysed the inflexible physical functionality of noise-cancelling headphones. While we relate to the human experience, it is the material regularities, constants or invariables that interest us the most. What we call the perceptual mechanics of noise-cancelling headphones can be expressed in mathematical formulas that show the combination of two physical influences on human perception: cancellation of sounds and addition of sounds.
(1) Cancellation means that A-entities are changed into non-auditory entities. Examples include positive experiences like removing painful, distracting noises like buskers, shrieking brakes, surroundings allowing for less attention or demanding more attention by other senses. Problematic experiences of noise cancellation could be missing warning sounds or announcements. This leads to increased vigilance with other senses.
(2) Addition means that mediated sound (Am-entities) are added by selecting an electronic source of sound. A-entities remain empty. Effects would be experiences of controlled attentive listening with good quality, immersion in self-selected sounds (Am-entities), and enjoyment.
Our study is particularly concerned with the computer logic necessary for creating intelligent attention management for urban users. The perceptual mechanics we have identified here can potentially inform design science projects. Presumably, the same features of attention management are transferable to other languages and cultures than English, and to other noisy settings such as an open office space, or while admitted at a hospital. A richer understanding of attention management with noise-cancelling headphones could be achieved with empirical studies in other contexts aiming to verify and/or improve on our theoretical hypothesis.
The article has design implications regarding the use of artificial intelligence to augment human perception. There is a potential to use the formulas in this article as input to the design of algorithms controlling the sound flows in noise-cancelling headphones. We see a particular use value for immersive storytelling and news. There are media design projects that explore complex augmented or virtual reality technologies for storytelling; for example, projects related to the Guardian and several Norwegian newspapers. The insights from this article can spur further development of advanced, smart, intelligent sonic interfaces.
The interviews were done in late 2013, when noise cancelling was not as developed as now, and results may therefore be inconsistent with the technological level reached today. Manual setting of noise-cancelling level has for example been realized in products like Bose QC35 and Libratone Q. Apple’s Airpods do not have (as of the time of writing) noise cancelling, but they have some intelligence in selecting which sounds you will hear. However, this again confirms that technology development moves in the ways we suggest; i.e., to support more complex computer-based attention management.
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