Your phd examination – the best defense is a good offense

Previously, I’ve written a few blog entries giving research advice, like ‘So you want to write a research paper‘ and ‘What a PhD thesis is really about… really!‘ I thought I’d come up with a good title for this blog entry, but then I saw this.


The PhD examination is certainly one of the most important moments in a researcher’s career. Its structure differs from country to country, institution to institution, and subject to subject. In some places, the PhD examination is open to the public, and failure is very rare. The student wouldn’t get to that stage unless the committee was confident that only minor issues remained. It might even be a bit of an event, with the committee wearing gowns and some of the student’s family attending.

But in most countries and most subjects it’s a bit more adversarial and passing is not guaranteed. It usually has a small committee. A public talk might be given, but the question and answer sessions are just the student and the committee.

There are lots and lots of guidance online about how to prepare for a PhD exam, and I’m not going to try to summarise them. Instead, I’ll give you some insights from my own experience, being examined, preparing others for a phd examination, or doing the examination myself. And having had experience with students who ranged from near flawless to, unfortunately, almost hopeless.

First off, congratulations for getting to this stage. That is already a major achievement. And keep in mind is that ultimately, it’s the document itself that is most important. If your thesis is strong, and you can explain it and discuss it well, then you’re already in a good position for the defense.


I’ve noticed that there are questions which seem relevant for me to ask in most PhD examinations, and other examiners tend to ask similar ones. So you can certainly prepare for them. The first are the sort of general PhD study questions; what’s it all about? Here’s a few typical ones.

  • Summarise your key findings?
  • What is your main contribution?
  • What is novel/significant/new?
  • What is the impact? your contribution to the field?
  • What are the weakest parts of your thesis?
  • Knowing what you know now, what would you change?

If there were aspects of your PhD study that were unusual, they also might ask you just to clarify things. For instance, I once examined a PhD whose research had taken a very long time. I wanted to know if there was research that hadn’t made it into the thesis, or whether there were technical issues that made the research more challenging. So I asked a question something like, ‘When did you start your phd research? Were there technical reasons it took so long?’ As it turned out, it was due to a perfectly understandable change of supervisor.

And the examiners will want to know what you know about your subject area and the state of the art.

  • Who else is doing research in this subject?
  • What are the most significant results in the last few years?
  • How does your approach differ from others?
  • Please characterise and summarise other approaches to your topic.

Then there will be some questions specific to your field. These questions might touch on the examiners’ knowledge, or on specific aspects of the literature that may or may not have been mentioned in the thesis.

  • Explain, in your own words, the following concepts -.
  • Compare the – and -. What are the fundamental differences?
  • Is all of your work relevant to other — challenges?
  • Why use —? Are there other approaches?
  • How does your work connect to — and — research?

And many examiners will want to know about the impact of the research so far, e.g. publications or demonstrators. If you do have any demonstrations (audio samples, videos, software, interfaces), it’s a good idea to present them, or at least be ready to present them.

  • Are the community aware of your work? Are people using your software?
  • Do you have any publications?
  • Which (other) results could you publish, and where?
  • Have you attended or presented at any conferences? What did you learn from them?


Then typically, the examiners start diving into the fine details of the thesis. So you should know where to find anything in your own document. Its also a good idea to reread your whole document a couple of days before the examination, so that its all fresh in your mind. It could have been a long time since you wrote it!


And best of luck to you!



My favorite sessions from the 143rd AES Convention


Recently, several researchers from the audio engineering research team here attended the 143rd Audio Engineering Society Convention in New York. Before the Convention, I wrote a blog entry highlighting a lot of the more interesting or adventurous research that was being presented there. As is usually the case at these Conventions, I have so many meetings to attend that I miss out on a lot of highlights, even ones that I flag up beforehand as ‘must see’. Still, I managed to attend some real gems this time, and I’ll discuss a few of them here.

I’m glad that I attended ‘Audio Engineering with Hearing Loss—A Practical Symposium’ . Hearing loss amongst musicians, audiophiles and audio engineers is an important topic that needs more attention. Overexposure, both prolonged and too loud, is a major cause of hearing dage. In addition to all the issues it causes for anybody, for those in the industry, it affects their ability to work or even appreciate their passion. The session had lots of interesting advice.

The most interesting presentation in the session was from Richard Einhorn, a composer and music producer. In 2010, he lost much of his hearing due to a virus. He woke up one day to find that he had completely lost hearing in his right ear, a condition known as Idiopathic Sudden Sensorineural Hearing Loss. This then evolved into hyperacusis, with extreme distortion, excessive volume and speech intelligibility. In many ways, deafness in the right ear would have been preferred. On top of that, his left ear suffered otosclerosis, where everything was at greatly reduced volume. And given that this was his only functioning ear, the risk of surgery to correct it was too great.

Richard has found some wonderful ways to still function, and even continue working in audio and music, with the limited hearing he still has. There’s a wonderful description of them in Hearing Loss Magazine, and they include the use of the ‘Companion Mic,’ which allowed him to hear from many different locations around a busy, noisy environment, like a crowded restaurant.

Thomas Lund presented ‘The Bandwidth of Human Perception and its Implications for Pro Audio.’ I really wasn’t sure about this before the Convention. I had read the abstract, and thought it might be some meandering, somewhat philosophical talk about hearing perception, with plenty of speculation but lacking in substance. I was very glad to be proven wrong! It had aspects of all of that, but in a very positive sense. It was quite rigorous, essentially a systematic review of research in the field that had been published in medical journals. It looks at the question of auditory perceptual bandwidth, where bandwidth is in a general information theoretic and cognitive sense, not specifically frequency range. The research revolves around the fact that, though we receive many megabits of sensory information every second, it seems that we only use dozens of bits per second of information in our higher level perception. This has lots of implications for listening test design, notably on how to deal with aspects like sample duration or training of participants. This was probably the most fascinating technical talk I saw at the Convention.

There were two papers that I had flagged up as having the most interesting titles, ‘Influence of Audience Noises on the Classical Music Perception on the Example of Anti-cough Candies Unwrapping Noise’, and ‘Acoustic Levitation—Standing Wave Demonstration.’ I had an interesting chat with an author of the first one, Adam Pilch. When walking around much later looking for the poster for the second one, I bump into Adam again. Turns out, he was a co-author on both of them! It looks like Adam Pilch and Bartlomiej Chojnacki (the shared authors on those papers) and their co-authors have an appreciation of the joy of doing research for fun and curiousity, and an appreciation for a good paper title.

Leslie Ann Jones was the Heyser lecturer. The Heyser lecture, named after Richard C. Heyser, is an evening talk given by an eminent individual in audio engineering or related fields. Leslie has had a fascinating career, and gave a talk that makes one realise just how much the industry is changing and growing, and how important are the individuals and opportunities that one encounters in a career.

The last session I attended was also one of the best. Chris Pike, who recently became leader of the audio research team at BBC R&D (he has big shoes to fill, but fits them well and is already racing ahead), presented ‘What’s This? Doctor Who with Spatial Audio!’ . I knew this was going to be good because it involved two of my favorite things, but it was much better than that. The audience were all handed headphones so that they could listen to binaural renderings used throughout the presentation. I love props at technical talks! I also expected the talk to focus almost completely on the binaural, 3d sound rendering for a recent episode, but it was so much more than that. There was quite detailed discussion of audio innovation throughout the more than 50 years of Doctor Who, some of which we have discussed when mentioning Daphne Oram and Delia Derbyshire in our blog entry on female pioneers in audio engineering.

There’s a nice short interview with Chris and colleagues Darran Clement (sound mixer) and Catherine Robinson (audio supervisor) about the binaural sound in Doctor Who on BBC R&D’s blog, and here’s a youtube video promoting the binaural sound in the recent episode;


The Audiovisual bounce-inducing effect (Bounce, bounce, bounce… Part II)

Last week we talked about bouncing sounds. Its very much a physical phenomenon, but a lot has been made of a perceptual effect sometimes referred to as the ‘Audiovisual bounce-inducing effect.’ The idea is that if someone is presented with two identical objects moving on a screen in opposing direction and crossing paths, they appear to do just that- cross paths. But if a short sound is played at the moment they first intersect, they appear to bounce off each other.

I’ve read a couple of papers on this, and browsed a few more, and I’ve yet to see anything interesting here.

Consider the figures below. On the left are the two paths taken by the two objects, one with short dashes in blue, one with long dashes in red. Since they are identical (usually just circles on a computer screen), it could just as easily be the paths shown on the right.


So which one is perceived? Well, two common occurrences are;

– Two objects, and one of them passes behind the other. This usually doesn’t produce a sound.
– Two objects, and they bounce off each other, producing the sound of a bounce.

If you show the objects without a sound, it perfectly matches the first scenario. It would be highly unlikely to perceive this as a bounce since then we would expect to hear something. On the other hand, if you play a short sound at the moment the two objects interact, even if it doesn’t exactly match a ‘bounce sound’, it is still a noise at the moment of visual contact. And so this is much more likely to be perceived as a bounce (which clearly produces a sound) than as passing by (which doesn’t). Further studies showed that the more ‘bounce-like’ the sound is, the more likely it is to be perceived as a bounce, and its less likely to be perceived as a bounce if similar sounds are also played when the objects do not intersect.

The literature gives all sorts of fanciful explanations for the basic phenomenon. And maybe someone can enlighten me as to why this is interesting. I suppose, if one begins with the assumption that auditory cues (even silence) do not play a role in perception of motion, then this may be surprising. But to me, this just seems to match everyday experience of sight and sound, and is intuitively obvious.

I should also note that in one of the papers on the ‘Audiovisual bounce-inducing effect’ (Watanabe 2001), the authors committed the cardinal sin of including one of the authors as a test subject and performing standard statistical analysis on the results. There are situations when this sort of thing may be acceptable or even appropriate*, but in which case one should be very careful to take that into account in any analysis and interpretation of results.

* In the following two papers, participants rated multrack audio mixes, where one of the mixes had been created by the participant. But this was intentional, to see whether the participant would rate their own mix highly.

And here’s just a few references on the audiovisual bounce inducing effect.

Grassi M, Casco C. Audiovisual bounce-inducing effect: When sound congruence affects grouping in vision. Attention, Perception, & Psychophysics. 2010 Feb 1;72(2):378-86.

Remijn GB, Ito H, Nakajima Y. Audiovisual integration: An investigation of the ‘streaming-bouncing’phenomenon. Journal of physiological anthropology and applied human science. 2004;23(6):243-7.

Watanabe K, Shimojo S. When sound affects vision: effects of auditory grouping on visual motion perception. Psychological Science. 2001 Mar;12(2):109-16.

Zeljko M, Grove PM. Sensitivity and Bias in the Resolution of Stream-Bounce Stimuli. Perception. 2017 Feb;46(2):178-204.

Bounce, bounce, bounce . . .


Another in our continuing exploration of everyday sounds (Screams, Applause, Pouring water) is the bouncing ball. It’s a nice one for a blog entry since there are only a small number of papers focused on bouncing, which means we can give a good overview of the field. It’s also one of those sounds that we can identify very clearly; we all know it when we hear it. It has two components that can be treated separately; the sound of a single bounce and the timing between bounces.

Let’s consider the second aspect. If we drop a ball from a certain height and ignore any drag, the time it takes to hit the ground is completely determined by gravity. When it hits the ground, some energy is absorbed on impact. And so it may be traveling downwards with a velocity v1 just before impact, and after impact travels upwards with velocity v2. The ratio v2/v1 is called the coefficient of restitution (COR). A high COR means that the ball travels back up almost to its original height, and a low COR means that most energy is absorbed and it only travels up a short distance.

Knowing COR, one can use simple equations of motion to determine the time between each bounce. And since the sum of the times between bounces is a convergent series, one can find the maximum time until it stops bouncing. Conversely, measuring the coefficient of friction from times between bounces is literally a tabletop physics experiment (Aguiar 2003, Farkas 2006, Schwarz 2013). And kinetic energy depends on the square of the velocity, so we know how much energy is lost with each bounce, which also gives an idea of how the sound levels of successive bounces should decrease.

[The derivation of all this has been left to the reader 😊. But again, its straightforward application of the equations of motion that give time dependence of position and velocity under constant acceleration]

Its not that hard to extend this approach, for instance by including air drag or sloped surfaces. But if you put the ball on a vibrating platform, all sorts of wonderful nonlinear behaviour can be observed; chaos, locking and chattering (Luck 1993).

For instance, have a look at the following video; which shows some interesting behaviour where bouncing balls all seem to organise onto one side of a partition.

So much for the timing of bounces, but what about the sound of a single bounce? Well, Nagurka (2004) modelled the bounce as a mass-spring-damper system, giving the time of contact for each bounce. It provides a little more realism by capturing some aspects of the bounce sound, Stoelinga (2007) did a detailed analysis of bouncing and rolling sounds. It has a wealth of useful information, and deep insights into both the physics and perception of bouncing, but stops short of describing how to synthesize a bounce.

To really capture the sound of a bounce, something like modal synthesis should be used. That is, one should identify the modes that are excited for impact of a given ball on a given surface, and their decay rates. Farnell measured these modes for some materials, and used those values to synthesize bounces in Designing Sound . But perhaps the most detailed analysis and generation of such sounds, at least as far as I’m aware, is in the work of Davide Rocchesso and his colleagues, leaders in the field of sound synthesis and sound design. They have produced a wealth of useful work in the area, but an excellent starting point is The Sounding Object.

Are you aware of any other interesting research about the sound of bouncing? Let us know.

Next week, I’ll continue talking about bouncing sounds with discussion of ‘the audiovisual bounce-inducing effect.’


  • Aguiar CE, Laudares F. Listening to the coefficient of restitution and the gravitational acceleration of a bouncing ball. American Journal of Physics. 2003 May;71(5):499-501.
  • Farkas N, Ramsier RD. Measurement of coefficient of restitution made easy. Physics education. 2006 Jan;41(1):73.
  • Luck, J.M. and Mehta, A., 1993. Bouncing ball with a finite restitution: chattering, locking, and chaos. Physical Review E, 48(5), p.3988.
  • Nagurka, M., Shuguang H,. “A mass-spring-damper model of a bouncing ball.” American Control Conference, 2004. Vol. 1. IEEE, 2004.
  • Schwarz O, Vogt P, Kuhn J. Acoustic measurements of bouncing balls and the determination of gravitational acceleration. The Physics Teacher. 2013 May;51(5):312-3.
  • Stoelinga C, Chaigne A. Time-domain modeling and simulation of rolling objects. Acta Acustica united with Acustica. 2007 Mar 1;93(2):290-304.

Our meta-analysis wins best JAES paper 2016!

Last year, we published an Open Access article in the Journal of the Audio Engineering Society (JAES) on “A meta-analysis of high resolution audio perceptual evaluation.”


I’m very pleased and proud to announce that this paper won the award for best JAES paper for the calendar year 2016.

We discussed the research a little bit while it was ongoing, and then in more detail soon after publication. The research addressed a contentious issue in the audio industry. For decades, professionals and enthusiasts have engaged in heated debate over whether high resolution audio (beyond CD quality) really makes a difference. So I undertook a meta-analysis to assess the ability to perceive a difference between high resolution and standard CD quality audio. Meta-analysis is a popular technique in medical research, but this may be the first time that its been formally applied to audio engineering and psychoacoustics. Results showed a highly significant ability to discriminate high resolution content in trained subjects that had not previously been revealed. With over 400 participants in over 12,500 trials, it represented the most thorough investigation of high resolution audio so far.

Since publication, this paper was covered broadly across social media, popular press and trade journals. Thousands of comments were made on forums, with hundreds of thousands of reads.

Here’s one popular independent youtube video discussing it.

and an interview with Scientific American about it,

and some discussion of it in this article for Forbes magazine (which is actually about the lack of a headphone jack in the iPhone 7).

But if you want to see just how angry this research made people, check out the discussion on hydrogenaudio. Wow, I’ve never been called an intellectually dishonest placebophile apologist before 😉 .

In fact, the discussion on social media was full of misinformation, so I’ll try and clear up a few things here;

When I first started looking into this subject , it became clear that potential issues in the studies was a problem. One option would have been to just give up, but then I’d be adding no rigour to a discussion because I felt it wasn’t rigourous enough. Its the same as not publishing because you don’t get a significant result, only now on a meta scale. And though I did not have a strong opinion either way as to whether differences could be perceived, I could easily be fooling myself. I wanted to avoid any of my own biases or judgement calls. So I set some ground rules.

  • I committed to publishing all results, regardless of outcome.
  • A strong motivation for doing the meta-analysis was to avoid cherry-picking studies. So I included all studies for which there was sufficient data for them to be used in meta-analysis.  Even if I thought a study was poor, its conclusions seemed flawed or it disagreed with my own conceptions, if I could get the minimal data to do meta-analysis, I included it. I then discussed potential issues.
  • Any choices regarding analysis or transformation of data was made a priori, regardless of the result of that choice, in an attempt to minimize any of my own biases influencing the outcome.
  • I did further analysis to look at alternative methods of study selection and representation.

I found the whole process of doing a meta-analysis in this field to be fascinating. In audio engineering and psychoacoustics, there are a wealth of studies investigating big questions, and I hope others will use similar approaches to gain deeper insights and perhaps even resolve some issues.

Exciting research at the upcoming Audio Engineering Society Convention


About five months ago, we previewed the last European Audio Engineering Society Convention, which we followed with a wrap-up discussion. The next AES  convention is just around the corner, October 18 to 21st in New York. As before, the Audio Engineering research team here aim to be quite active at the convention.

These conventions are quite big, with thousands of attendees, but not so large that you get lost or overwhelmed. Away from the main exhibition hall is the Technical Program, which includes plenty of tutorials and presentations on cutting edge research.

So here, we’ve gathered together some information about a lot of the events that we will be involved in, attending, or we just thought were worth mentioning. And I’ve gotta say, the Technical Program looks amazing.


One of the first events of the Convention is the Diversity Town Hall, which introduces the AES Diversity and Inclusion Committee. I’m a firm supporter of this, and wrote a recent blog entry about female pioneers in audio engineering. The AES aims to be fully inclusive, open and encouraging to all, but that’s not yet fully reflected in its activities and membership. So expect to see some exciting initiatives in this area coming soon.

In the 10:45 to 12:15 poster session, Steve Fenton will present Alternative Weighting Filters for Multi-Track Program Loudness Measurement. We’ve published a couple of papers (Loudness Measurement of Multitrack Audio Content Using Modifications of ITU-R BS.1770, and Partial loudness in multitrack mixing) showing that well-known loudness measures don’t correlate very well with perception when used on individual tracks within a multitrack mix, so it would be interesting to see what Steve and his co-author Hyunkook Lee found out. Perhaps all this research will lead to better loudness models and measures.

At 2 pm, Cleopatra Pike will present a discussion and analysis of Direct and Indirect Listening Test Methods. I’m often sceptical when someone draws strong conclusions from indirect methods like measuring EEGs and reaction times, so I’m curious what this study found and what recommendations they propose.

The 2:15 to 3:45 poster session will feature the work with probably the coolest name, Influence of Audience Noises on the Classical Music Perception on the Example of Anti-cough Candies Unwrapping Noise. And yes, it looks like a rigorous study, using an anechoic chamber to record the sounds of sweets being unwrapped, and the signal analysis is coupled with a survey to identify the most distracting sounds. It reminds me of the DFA faders paper from the last convention.

At 4:30, researchers from Fraunhofer and the Technical University of Ilmenau present Training on the Acoustical Identification of the Listening Position in a Virtual Environment. In a recent paper in the Journal of the AES, we found that training resulted in a huge difference between participant results in a discrimination task, yet listening tests often employ untrained listeners. This suggests that maybe we can hear a lot more than what studies suggest, we just don’t know how to listen and what to listen for.


If you were to spend only one day this year immersing yourself in frontier audio engineering research, this is the day to do it.

At 9 am, researchers from Harman will present part 1 of A Statistical Model that Predicts Listeners’ Preference Ratings of In-Ear Headphones. This was a massive study involving 30 headphone models and 71 listeners under carefully controlled conditions. Part 2, on Friday, focuses on development and validation of the model based on the listening tests. I’m looking forward to both, but puzzled as to why they weren’t put back-to-back in the schedule.

At 10 am, researchers from the Tokyo University of the Arts will present Frequency Bands Distribution for Virtual Source Widening in Binaural Synthesis, a technique which seems closely related to work we presented previously on Cross-adaptive Dynamic Spectral Panning.

From 10:45 to 12:15, our own Brecht De Man will be chairing and speaking in a Workshop on ‘New Developments in Listening Test Design.’ He’s quite a leader in this field, and has developed some great software that makes the set up, running and analysis of listening tests much simpler and still rigorous.

In the 11-12:30 poster session, Nick Jillings will present Automatic Masking Reduction in Balance Mixes Using Evolutionary Computing, which deals with a challenging problem in music production, and builds on the large amount of research we’ve done on Automatic Mixing.

At 11:45, researchers from McGill will present work on Simultaneous Audio Capture at Multiple Sample Rates and Formats. This helps address one of the challenges in perceptual evaluation of high resolution audio (and see the open access journal paper on this), ensuring that the same audio is used for different versions of the stimuli, with only variation in formats.

At 1:30, renowned audio researcher John Vanderkooy will present research on how a  loudspeaker can be used as the sensor for a high-performance infrasound microphone. In the same session at 2:30, researchers from Plextek will show how consumer headphones can be augmented to automatically perform hearing assessments. Should we expect a new audiometry product from them soon?

At 2 pm, our own Marco Martinez Ramirez will present Analysis and Prediction of the Audio Feature Space when Mixing Raw Recordings into Individual Stems, which applies machine learning to challenging music production problems. Immediately following this, Stephen Roessner discusses a Tempo Analysis of Billboard #1 Songs from 1955–2015, which builds partly on other work analysing hit songs to observe trends in music and production tastes.

At 3:45, there is a short talk on Evolving the Audio Equalizer. Audio equalization is a topic on which we’ve done quite a lot of research (see our review article, and a blog entry on the history of EQ). I’m not sure where the novelty is in the author’s approach though, since dynamic EQ has been around for a while, and there are plenty of harmonic processing tools.

At 4:15, there’s a presentation on Designing Sound and Creating Soundscapes for Still Images, an interesting and unusual bit of sound design.


Judging from the abstract, the short Tutorial on the Audibility of Loudspeaker Distortion at Bass Frequencies at 5:30 looks like it will be an excellent and easy to understand review, covering practice and theory, perception and metrics. In 15 minutes, I suppose it can only give a taster of what’s in the paper.

There’s a great session on perception from 1:30 to 4. At 2, perceptual evaluation expert Nick Zacharov gives a Comparison of Hedonic and Quality Rating Scales for Perceptual Evaluation. I think people often have a favorite evaluation method without knowing if its the best one for the test. We briefly looked at pairwise versus multistimuli tests in previous work, but it looks like Nick’s work is far more focused on comparing methodologies.

Immediately after that, researchers from the University of Surrey present Perceptual Evaluation of Source Separation for Remixing Music. Techniques for remixing audio via source separation is a hot topic, with lots of applications whenever the original unmixed sources are unavailable. This work will get to the heart of which approaches sound best.

The last talk in the session, at 3:30 is on The Bandwidth of Human Perception and its Implications for Pro Audio. Judging from the abstract, this is a big picture, almost philosophical discussion about what and how we hear, but with some definitive conclusions and proposals that could be useful for psychoacoustics researchers.


Grateful Dead fans will want to check out Bridging Fan Communities and Facilitating Access to Music Archives through Semantic Audio Applications in the 9 to 10:30 poster session, which is all about an application providing wonderful new experiences for interacting with the huge archives of live Grateful Dead performances.

At 11 o’clock, Alessia Milo, a researcher in our team with a background in architecture, will discuss Soundwalk Exploration with a Textile Sonic Map. We discussed her work in a recent blog entry on Aural Fabric.

In the 2 to 3:30 poster session, I really hope there will be a live demonstration accompanying the paper on Acoustic Levitation.

At 3 o’clock, Gopal Mathur will present an Active Acoustic Meta Material Loudspeaker System. Metamaterials are receiving a lot of deserved attention, and such advances in materials are expected to lead to innovative and superior headphones and loudspeakers in the near future.


The full program can be explored on the Convention Calendar or the Convention website. Come say hi to us if you’re there! Josh Reiss (author of this blog entry), Brecht De Man, Marco Martinez and Alessia Milo from the Audio Engineering research team within the Centre for Digital Music  will all be there.


Aural fabric

This is a slightly modified version of a post that originally appeared on the Bela blog.

Alessia Milo is an architect currently researching education in acoustics for architecture while pursuing her PhD  with the audio engineering team here, as well as with the Media and Arts Technology programme.

She will present Influences of a Key Map on Soundwalk Exploration with a Textile Sonic Map at the upcoming AES Convention.

Here, she  introduces Aural Fabric, a captivating interactive sound installation consisting of a textile map which plays back field recordings when touched.

Aural Fabric is an interactive textile map allowing you to listen to selected field recordings by touching areas of the map that can sense touch. It uses conductive thread, capacitive sensing and Bela to process sensor data and play back the field recordings. The first map that was made represents a selection of sounds from the area of Greenwich, London. The field recordings of the area were captured with binaural microphones as part of a group soundwalk as part of a study on sonic perception. For the installation I chose recordings of particular locations that have a unique sonic identity, which you can listen to here. The textile map was created as a way of presenting these recordings to the general public.

When I created this project I wanted people to be able to explore the fabric surface of the map and hear the field recordings of the specific locations on the map as they touched it. An interesting way to do this was with conductive thread that I could embroider into the layout of the map. To read the touches from the conductive areas of the map I decided to use the MPR121 capacitive touch sensing board along with a Bela board.

Designing the map


I first considered the scale of the map based on how big the conductive areas could be in order to be touched comfortably, and on the limits of the embroidery machine used (Brother Pr1000E) . I finally settled on a 360mmx200mm frame. The vector traces from the map of the area (retrieved from OpenStreetMap) were reduced to the minimum amount needed to make the map recognizable and easily manageable by the embroidery PE-Design 10 software, which I used to transform the shapes into filling patterns.

Linen was chosen as the best material for the fabric base due to its availability, resistance and plain-aesthetic qualities. I decided to represent the covered areas we entered during the soundwalk as coloured reliefs completely made of grey/gold conductive thread. The park areas were left olive-green if not interactive and green mixed with the conductive thread if interactive. This was to allow the map to be clearly understood in its different elements. Courtyards we crossed were embroidered as flat areas in white with parts in conductive thread, whilst landmarks were represented with a mixture of pale grey, with conductive thread only on the side where the walk took place.

The River Thames, also present in the recordings, was depicted as a pale blue wavy surface with some conductive parts close to the sides where the walk took place. Buildings belonging to the area but not covered in the soundwalk were represented in flat pale grey hatch.

The engineering process

The fabric was meticulously embroidered with coloured rayon and conductive threads thanks to the precision of the embroidery machine. I tested the conductive thread and the different stitch configurations on a small sample of fabric to determine how well the capacitive charges and discharges caused by touching the conductive parts could be read by the breakout board.

The whole map consists of a graphical layer, an insulation layer, an embroidered circuit layer, a second insulation layer, and a bottom layer in neoprene which works as a soft base. Below the capacitive areas of the top layer I cut some holes in the insulation layer to allow the top layer to communicate with the circuit layer. Some of these areas have been also manually stitched to the circuit layer to keep the two layers in place. The fabric can be easily rolled and moved separately from the Bela board.

Some of the embroidered underlying traces. The first two traces appear too close in one point: when the fabric is not fully stretched they risk being triggered together!

Stitching the breakout board

Particular care was taken when connecting the circuit traces in the inner embroidered circuit layer to the capacitive pins of the breakout board. As this connection needs to be extremely solid it was decided to solder some conductive wire to the board, pass it through the holes beforehand, and then stitch the wires one by one to the correspondent conductive thread traces, which were previously embroidered.

Some pointers came from the process of working with the conductive thread:

  • Two traces should never be too close to one another or they will trigger false readings by shorting together.
  • A multimeter comes in handy to verify the continuity of the circuit. To avoid wasting time and material, it’s better to check for continuity on some samples before embroidering the final one as the particular materials and threads in use can behave very differently.
  • Be patient and carefully design your circuit according to the intended position of the capacitive boards. For example, I decided to place the two of them (to allow for 24 separate readings) in the top corners of the fabric.

Connecting with Bela:

The two breakout boards are connected through i2c to Bela which receives the readings from each pin of the breakout boards. The leftmost is connected through i2c to the other one, and this one goes to Bela. This cable is the only connection between the Fabric and Bela. It is possible to set an independent threshold for each pin, which will trigger the index releasing the correspondent recording. The code used to read the capacitive touch breakout board comes with the board and can be found here: examples/06-Sensors/capacitive-touch/.

MPR121 capacitive touch sensing breakout board connected to the i2c terminals of Bela.

The code to handle the recordings was nicely tweaked by Christian Heinrichs to add a natural fade in and fade out for the recordings. This code is based on the multi sample streamer example already available in Bela’s IDE which can be found here: examples/04-Audio/sample-streamer-multi/. Each recording has a pointer that keeps track of where the recording paused, so that touching the corresponding area again will resume playing from that point and not from the beginning. Multiple areas can be played at the same time allowing you to create experimental mixes of different ambiances.

Exhibition setting

This piece is best experienced through headphones as the recordings were made using binaural microphones. Nevertheless it is also possible to use speakers, with some loss of the spatial sonic image fidelity. In either case the audio output is taken directly from the Bela board. In the photograph below I made a wooden and perspex case for the board to protect it while it was installed in a gallery and powered the board with a USB 5V phone charger. Bela was set to run this project on start-up making it simple for gallery assistants to turn the piece on and off. The Aural Fabric is used for my PhD research, focused on novel approaches to strengthening the relationship between architecture and acoustics.  I’m engaging architecture students in sonic explorations and reflections on how architecture and its design contributes to defining our sonic environments.

Aural Fabric: Greenwich has been displayed at Sonic Environments in Brisbane among the installations and Inter/sections 2016 in London. More information documenting the making process is available here.