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.



Sound Effects Taxonomy

At the upcoming International Conference on Digital Audio Effects, Dave Moffat will be presenting recent work on creating a sound effects taxonomy using unsupervised learning. The paper can be found here.

A taxonomy of sound effects is useful for a range of reasons. Sound designers often spend considerable time searching for sound effects. Classically, sound effects are arranged based on some key word tagging, and based on what caused the sound to be created – such as bacon cooking would have the name “BaconCook”, the tags “Bacon Cook, Sizzle, Open Pan, Food” and be placed in the category “cooking”. However, most sound designers know that the sound of frying bacon can sound very similar to the sound of rain (See this TED talk for more info), but rain is in an entirely different folder, in a different section of the SFx Library.

The approach, is to analyse the raw content of the audio files in the sound effects library, and allow a computer to determine which sounds are similar, based on the actual sonic content of the sound sample. As such, the sounds of rain and frying bacon will be placed much closer together, allowing a sound designer to quickly and easily find related sounds that relate to each other.

Here’s a figure from the paper, comparing the generated taxonomy to the original sound effect library classification scheme.


12th International Audio Mostly Conference, London 2017

by Rod Selfridge & David Moffat. Photos by Beici Liang.

Audio Mostly – Augmented and Participatory Sound and Music Experiences, was held at Queen Mary University of London between 23 – 26 August. The conference brought together a wide variety of audio and music designers, technologists, practitioners and enthusiasts from all over the world.

The opening day of the conference ran in parallel with the Web Audio Conference, also being held at Queen Mary, with sessions open to all delegates. The day opened with a joint Keynote from the computer scientist and author of the highly influential sound effect book – Designing Sound, Andy Farnell. Andy covered a number of topics and invited audience participation which grew into a discussion regarding intellectual property – the pros and cons if it was done away with.

Andy Farnell

The paper session then opened with an interesting talk by Luca Turchet from Queen Mary’s Centre for Digital Music. Luca presented his paper on The Hyper Mandolin, an augmented music instrument allowing real-time control of digital effects and sound generators. The session concluded with the second talk I’ve seen in as many months by Charles Martin. This time Charles presented Deep Models for Ensemble Touch-Screen Improvisation where an artificial neural network model has been used to implement a live performance and sniffed touch gestures of three virtual players.

In the afternoon, I got to present my paper, co-authored by David Moffat and Josh Reiss, on a Physically Derived Sound Synthesis Model of a Propeller. Here I continue the theme of my PhD by applying equations obtained through fluid dynamics research to generate authentic sound synthesis models.

Rod Selfridge

The final session of the day saw Geraint Wiggins, our former Head of School at EECS, Queen Mary, present Callum Goddard’s work on designing Computationally Creative Musical Performance Systems, looking at questions like what makes performance virtuosic and how this can be implemented using the Creative Systems Framework.

The oral sessions continued throughout Thursday, one presentation that I found interesting was by Anna Xambo titles Turn-Taking and Chatting in Collaborative Music Live Coding. In this research the authors explored collaborative music live coding using the live coding environment and pedagogical tool EarSketch, focusing on the benefits to both performance and education.

Thursday’s Keynote was by Goldsmith’s Rebecca Fiebrink, who was mentioned in a previous blog, discussing how machine learning can be used to support human creative experiences, aiding human designers for rapid prototyping and refinement of new interactions within sound and media.

Rebecca Fiebrink

The Gala Dinner and Boat Cruise was held on Thursday evening where all the delegates were taken on a boat up and down the Thames, seeing the sites and enjoying food and drink. Prizes were awarded and appreciation expressed to the excellent volunteers, technical teams, committee members and chairpersons who brought together the event.

Tower Bridge

A session on Sports Augmentation and Health / Safety Monitoring was held on Friday Morning which included a number of excellent talks. The presentation of the conference went to Tim Ryan who presented his paper on 2K-Reality: An Acoustic Sports Entertainment Augmentation for Pickup Basketball Play Spaces. Tim re-contextualises sounds appropriated from a National Basketball Association (NBA) video game to create interactive sonic experiences for players and spectators. I was lucky enough to have a play around with this system during a coffee break and can easily see how it could give an amazing experience for basketball enthusiasts, young and old, as well as drawing in a crowd to share.

Workshops ran on Friday afternoon. I went to Andy Farnell’s Zero to Hero Pure Data Workshop where participants managed to go from scratch to having a working bass drum, snare and high-hat synthesis models. Andy managed to illustrate how quickly these could be developed and included in a simple sequencer to give a basic drum machine.

Throughout the conference a number of fixed media, demos were available for delegates to view as well as poster sessions where authors presented their work.

Alessia Milo

Live music events were held on both Wednesday and Friday. A joint session titled Web Audio Mostly Concert was held on Wednesday which was a joint event for delegates of Audio Mostly and the Web Audio Conference. This included an augmented reality musical performance, a human-playable robotic zither, the Hyper Mandolin and DJs.

The Audio Mostly Concert on the Friday included a Transmusicking performance from a laptop orchestra from around the world, where 14 different performers collaborated online. The performance was curated by Anna Xambo. Alan Chamberlain and David De Roure performed The Gift of the Algorithm, which was a computer music performance inspired by Ada Lovelace. The wood and the water was an immersive performance of interactivity and gestural control of both a Harp and lighting for the performance, by Balandino Di Donato and Eleanor Turner. GrainField, by Benjamin Matuszewski and Norbert Schnell, was an interactive audio performance that demanded entire audience involvement, for the performance to exist, this collective improvisational piece demonstrated a how digital technology can really be used to augment the traditional musical experience. GrainField was awarded the prize for the best musical performance.

Adib Mehrabi

The final day of the conference was a full day’s workshop. I attended the one titled Designing Sounds in the Cloud. The morning was spent presenting two ongoing European Horizon 2020 projects, Audio Commons ( and Rapid-Mix. The Audio Commons initiative aims to promote the use of open audio content by providing a digital ecosystem that connects content providers and creative end users. The Rapid-Mix project focuses on multimodal and procedural interactions leveraging on rich sensing capabilities, machine learning and embodied ways to interact with sound.

Before lunch we took part in a sound walk around the Queen Mary Mile End Campus, with one of each group blindfolded, informing the other what they could hear. The afternoon session had teams of participants designing and prototyping new ways to use the APIs from each of the two Horizon 2020 projects – very much in the feel of a hackathon. We devised a system which captured expressive Italian hand gestures using the Leap Motion and classified them using machine learning techniques. Then in pure data each new classification triggered a sound effect taken from the Freesound website (part of the audio commons project). If time would have allowed the project would have been extended to have pure data link to the audio commons API and play sound effects straight from the web.

Overall, I found the conference informative, yet informal, enjoyable and inclusive. The social events were spectacular and ones that will be remembered by delegates for a long time.

Behind the spectacular sound of ‘Dunkirk’ – with Richard King: — A Sound Effect

The post Behind the spectacular sound of ‘Dunkirk’ – with Richard King: appeared first on A Sound Effect. Its an interesting interview giving deep insights into sound design and soundscape creation for film. It caught my attention first because of the mention of Richard King. But its not Richard King, Grammy award winning professor in sound recording at University of McGill. Its the other one, the Oscar award winning supervising sound editor at Warner Brothers Sound.

We collaborated with Prof. Richard King on a couple of papers. In [1], we conducted an experiment where eight songs were each mixed by eight different engineers. We analysed audio features from the multitracks and mixes. This allowed us to test various assumed rules of mixing practice. In the follow-up [2], the mixes were all rated by experienced test subjects. We used the ratings to investigate relationships between perceived mix quality and sonic features of the mixes.

[1] B. De Man, M. Boerum, B. Leonard, R. King, G. Massenburg and J. D. Reiss, ‘Perceptual Evaluation of Music Mixing Practices,’ 138th Audio Engineering Society (AES) Convention, May 2015

[2] B. De Man, B. Leonard, R. King and Joshua D. Reiss, “An analysis and evaluation of audio features for multitrack music mixtures,” 15th Int. Society for Music Information Retrieval Conference (ISMIR-14), Taipei, Taiwan, Oct. 2014

via Behind the spectacular sound of ‘Dunkirk’ – with Richard King: — A Sound Effect

Why can you hear the difference between hot and cold water ?

I recently found out about an interesting little experiment where it was shown that people could identify when hot or cold water was being poured from the sound alone. This is a little surprising since we don’t usually think of temperature as having a sound.
Here are two sound samples;

Which one do you think was hot water and which was cold water? Scroll down for the answer..




Keep scrolling
Yes, the first sound sample was cold water being poured, and the second was hot water.
The work was first done by a London advertising agency, Condiment Junkie, who use sound design in branding and marketing, in collaboration with researchers from University of Oxford, and they published a research paper on this. The experiment is first described in Condiment Junkie’s blog, and was picked up by NPR and lots of others. There’s even a YouTube video about this phenomenon that has over 600,000 views.
However, there wasn’t really a good explanation as to why we hear the difference. The academic paper did not really discuss this. The youtube video simply states ‘change in the splashing of the water changes the sound that it makes because of various complex fluid dynamic reasons,’ which really doesn’t explain anything. According to one of the founders of Condiment Junkie, “more bubbling in a liquid that’s hot… you tend to get higher frequency sounds from it,” but further discussion on NPR noted “Cold water is more viscous… That’s what makes that high pitched ringing.” Are they both right? There is even a fair amount of discussion of this on physics forums.
But its all speculation. Most of the arguments are half-formed and involve a fair amount of handwaving. No one actually analysed the audio.

So I put the two samples above through some analysis using Sonic Visualiser. Spectrograms are very good for this sort of thing because they show you how the frequency content is changing over time. But you have to be careful because if you don’t choose how to visualise it carefully, you’ll easily overlook the interesting stuff.

Here’s the spectrograms of the two files, cold water on top, hot water on bottom. Frequency is on a log scale (otherwise all the detail will be crammed at the bottom) and the peak frequencies are heavily emphasised (there’s an awful lot of noise).



There’s more analysis than shown, but the most striking feature is that the same frequencies are present in both signals! There is a strong, dominant frequency that linearly increases from about 650 Hz to just over 1 kilohertz. And there is a second frequency that appears a little later, starting at around 720 Hz, falling all the way to 250 Hz, then climbing back up again.

These frequencies are pretty much the same in both hot and cold cases. The difference is mainly that cold water has a much stronger second frequency (the one that dips).
So all those people who speculated on why and how hot and cold water sound different seem to have gotten it wrong. If they had actually analysed the audio, they would have seen that the same frequencies are produced, but with different strengths.
My first guess was that the second frequency is due to the size of water droplets being dependent on the rate of water flow. When more water is flowing, in the middle of the pour, the droplets are large and so produce lower frequencies. Hot water is less viscuous (more runny) and so doesn’t separate into these droplets so much.
I was less sure about the first frequency. Maybe this is due to a default droplet size, and only some water droplets have a larger size. But why would this first frequency be linearly increasing? Maybe after water hits the surface, it always separates into small droplets and so this is them splashing back down after initial impact. Perhaps, the more water on the floor, the smaller the droplets splashing back up, giving the increase in this frequency.
But Rod Selfridge, a researcher in the Audio Engineering team here, gave a better possible explanation, which I’ll repeat verbatim here.
The higher frequency line in the spectrogram which linearly increases could be related to the volume of air left in the vessel the liquid is being poured into. As the fluid is poured in the volume of air decreases and the resonant frequency of the remaining ‘chamber’ increases.
The lower line of frequencies could be related to the force of liquid being added. As the pouring speed increases, increasing the force, the falling liquid pushes further into the reservoir. This means a deeper column of air is trapped and becomes a bubble. The larger the bubble the lower the resonant frequency. This is the theory of Minneart and described in the attached paper.
My last thought was that for hot water, especially boiling, there will be steam in the vessel and surrounding the contact area of the pour. Perhaps the steam has an acoustic filtering effect and/or a physical effect on the initial pour or splashes.
 Of course, a more definitive answer would involve a few experiments, pouring differing amounts of water into differing containers. But I think this already demonstrates the need to test the theory of what sound will occur against analysis of the actual sounds produced.


Audio and informatics researchers are perhaps quite familiar with retrieval systems that try to analyse recordings to identify when an important word or phrase was spoken, or when a song was played. But I once did some collaboration with a company who did laughter and question detection, two audio informatics problems I hadn’t heard of before. I asked them about it. The company was developing audio analytics software to assist Call Centres. Call Centres wanted to keep track of the unusual or problematic calls, and in particular, any laughter when someone is calling tech support would be worth investigating. And I suppose all sorts of unusual sounds should indicate that something about the call is worth noting. Which brings me to the subject of this blog entry.



Screams occupy an important evolutionary niche, since they are used as a warning and alert signal, and hence are intended to be a sound which we strongly and quickly focus on. A 2015 study by Arnal et al. showed that screams contain a strong modulation component, typically within the 30 to 150 Hz range. This sort of modulation is sometimes called roughness. Arnal showed that roughness occurs in both natural and artificial alarm sounds, and that adding roughness to a sound can make it be perceived as more alarming or fearful.

This new study suggests that a peculiar set of features may be appropriate for detecting screams. And like most fields of research, if you dig deep enough, you find that quite a few people have already scratched the surface.

I did a quick search of AES and IEEE papers and found ten that had ‘scream’ in the title, not counting those referring to systems or algorithms given the acronym SCREAM. This is actually very few, indicating that the field is underdeveloped. One of them, is really about screams and growls in death metal music, which though interesting in its own right, is quite different. Most of the rest all seem to mostly just ‘applying my favourite machine learning technique to scream data’. This is an issue with a lot of papers, deserving of a blog entry in future.

But one of the most detailed analyses of screams was conducted by audio forensics researcher and consultant Durand Begault. In 2008 he published  ‘Forensic Analysis of the Audibility of Female Screams’ In it, he notes “the local frequency modulation (‘warble’ or ‘vibrato’)” that was later focused on in Arnal’s paper.

Begault also has some interesting discussion of investigations of scream audibility for a court case. He was asked to determine whether a woman screaming in one location could be heard by potential witnesses in a nearby community. He tested this on site by playing back prerecorded screams at the site of the incident. The test screams were generated by asking female subjects ‘to scream as loudly as possible, as if you had just been surprised by something very scary.’ Thirty screams were recorded, ranging from 123 to 102 decibels. The end result was that these screams could easily be heard more than 100 meters away, even with background noise and obstructions.

This is certainly not the only audio analysis and processing that has found its way into the courtroom. One high profile case was in February 2012. Neighborhood watch coordinator George Zimmerman shot and killed black teenager Trayvon Martin in Sanford, Florida. In Zimmerman’s trial for second degree murder, experts offered analysis of a scream heard in the background of a 911 phone call that also captured the sound of the gunshot that killed Martin. If the screamer was Zimmerman, it would strengthen the case that he acted in self-defense, but if it was Martin, it would imply that Zimmerman was the aggressor. But FBI audio analysis experts testified in the case about the difficulties in identifying the speaker, or even his age, from the screams , and news outlets also called on experts who noted the lack of robust ‘screamer identification’ technologies.

The issue of scream audibility thus begs the question, ‘how loud is a scream.’ We know they can be attention-grabbing, ear –piercing shrieks. The loudest scream Begault recorded was 123 dB, and he stated that scream “frequency content seems almost tailored to frequencies of maximal sensitivity on an equal-loudness contour.”

And apparently, one can get a lot louder with a scream than a shout. According to the Guinness Book of World Records, the loudest shout was 121.7 dBA by Annalisa Flanagan, shouting the word ‘Quiet!’. And the loudest scream ever recorded is 129 dB (C-Weighted), by Jill Drake. Not surprisingly, both Jill and Annalisa are teachers, who seem to have found a very effective way to deal with unruly classrooms.

Interestingly, one might have a false conception of the diversity of screaming sounds if one’s understanding is based on films. The Wilhelm Scream, a sound sample that has been used in over 300 films. This overuse perhaps gives a certain familiarity to the listener, and lessens the alarming nature of the sound.

For more on the Wilhelm scream, see the blog entry ‘Swinging microphones and slashing lightsabres’. But here’s a short video on the sound, which includes a few more examples of its use than were given in the previous blog entry.

Sound Synthesis of an Aeolian Harp


Synthesising the Aeolian harp is part of a project into synthesising sounds that fall into a class called aeroacoustics. The synthesis model operates in real-time and is based on the physics that generate the sounds in nature. 

The Aeolian harp is an instrument that is played by the wind. It is believed to date back to ancient Greece; legend states that King David hung a harp in the tree to hear it being played by the wind. They became popular in Europe in the romantic period and Aeolian harps can be designed as garden ornaments, part of sculptures or large scale sound installations.  

The sound created by Aeolian harp has often been described as meditative and inspiring. A poem by Ralph Emerson describes it as follows:
Keep your lips or finger-tips
For flute or spinet’s dancing chips; 
I await a tenderer touch
I ask more or not so much:

Give me to the atmosphere.


The harp in the picture is taken from Professor Henry Gurr’s website. This has an excellent review of the principles behind design and operation of Aeolian harps. 
Basic Principles

As air flows past a cylinder vortices are shed at a frequency that is proportional to the cylinder diameter and speed of the air. This has been discussed in the previous blog entry on Aeolian tones. We now think of the cylinders as a string, like that of a harp, guitar, violin, etc. When a string of one of these instruments is plucked it vibrates at it’s natural frequency. The natural frequency is proportional to the tension, length and mass of the string.  

Instead of a pluck or a bow exciting a string, in an Aeolian harp it is the vortex shedding that stimulates the strings. When the frequency of the vortex shedding is in the region of the natural vibration frequency of the string, or one of it’s harmonics, a phenomenon known as lock-in occurs. While in lock-in the string starts to vibrate at the relevant harmonic frequency. For a range of airspeed the string vibration is the dominant factor that dictates the frequency of the vortex shedding; changing the air speed does not change the frequency of vortex shedding, hence the process is locked-in. 

While in lock-in a FM type acoustic output is generated giving the harp its unique sound, described by the poet Samuel Coleridge as a “soft floating witchery of sound”.
Our Model 

As with the Aeolian tone model we calculate the frequency of vortex shedding for a given string dimensions and airspeed. We also calculate the fundamental natural vibrational frequency and harmonics of a string given its properties. 

There is a specific area of airspeed that leads to string vibration and vortex shedding locking in. This is calculated and the specific frequencies for the FM acoustic signal generated. There is a hysteresis effect on the vibration amplitude based on the increase and decrease of the airspeed which is also implemented. 

 A used interface is provided that allows a user to select up to 13 strings, adjusting their length, diameter, tension, mass and the amount of damping (which reduces the vibration effects as the harmonic number increases). This interface is shown below which includes presets of an number of different string and wind configurations. 

A copy of the pure data patch can be downloaded here. The video below was made to give an overview of the principles, sounds generated and variety of Aeolian harp constructions.