<![CDATA[SOUND FOCUS - Blog: Sculpting Sound]]>Fri, 25 Dec 2015 10:26:53 -0800Weebly<![CDATA[Sculpting with sound]]>Fri, 19 Jun 2015 07:46:46 GMThttp://soundfocus.weebly.com/blog-sculpting-sound/sculpting-with-sound
For many years "acoustic levitation" was a technique in search of an application: just like light waves, sound waves apply force to objects, but for audio frequencies the force is tiny unless the sound level is enormous. Ultrasonic frequencies pack a much bigger punch and, since they are inaudible, are rather more user friendly. Nevertheless, except under very controlled conditions the radiation pressure is still very small. 

Recently however, it has become possible to mould ultrasonic sound fields to form keyboards made of sound (see, for example, http://www.newscientist.com/article/dn26463-ultrasound-makes-hologram-keyboard-touchyfeely.html). At least, that's what they feel like: the examples currently available use infrared detectors link to pattern recognisers to determine the positions of a user's fingers. Ultrasound beams are then focussed at the fingertips, generating a pressure on them. So in fact the keyboard only exists at the points where it is felt; a kind of relative acoustic object.

In principle, one could generate all sorts of shapes in this way. Different textures could also be produced : the details of such an acoustic sculpture are limited by the wavelength of the sounds used to mould it.

At the cost of many more ultrasonic projecting elements and a lot more processing power, acoustic objects which are there all the time, whether they are touched or not, could be made too. If the idea of invisible but feelable objects seems a bit unsatisfactory, suspended particles are very easy to levitate, so one could make objects from smoke or mist or even glitter.

It's easy to imagine all sorts of applications for such things : art objects, theatre effects, virtual reality games and systems without the need to dress up like a robot, training facilities, control systems.

There is, unfortunately, a "but"... ultrasound is absorbed very rapidly by air, so the objects could be formed only within a very few centimetres of the array of projectors. There are two possible ways round this, however. Ultrasound travels much further underwater than in air, so much larger submerged acoustic shapes could be formed : acting as virtual walls to separate sharks from divers for example, or for fishing. Conceivably, one could also make subterranean structures (ultrasound travels easily underground too), like temporary walls or baffles to support the ground after earthquakes perhaps, or even for tunnelling

Another possibility would be to overcome the main limitations of audible sound by using what is known as a parametric array. This enables sounds of even very low frequency to be formed into precise beams. These beams could be made quite powerful, since they would be silent unless aimed directly at the ear or bounced from a surface (I've added a short explanation of how these arrays work below).

A key characteristic of acoustic pressure-beams, of whatever frequency, is that they can only apply a force in the direction in which they are sent. So, while it is simple enough to make a flat or gently curving shape by using a panel covered by a layer of small acoustic projectors, to make something like a sphere or a hand-shape, there would have to be projectors in every direction - but one could imagine the walls, floor and ceiling of a gallery or wall being coated with such projectors, along with infrared detectors. A great deal of processing power would be needed to work out where people and other inconvenient objects are in the room, and literally work round them to make the shapes - and the projectors and sensors would need to be small, cheap, efficient and precise, but ever-faster processor speeds and ever-better MEMS (MicroElectroMechanical Systems) will soon be able to deliver both.


BACKGROUND : SOUND PROJECTION BY PARAMETRIC ARRAYS

When a sound wave is produced by a loudspeaker (or by any other source), it will tend to radiate in all directions as long as its wavelength is much longer than the loudspeaker (source) size. Hence, if you speak in the open air, your lower tones can be heard by someone standing behind you, because they are a few hundred Hz, corresponding to wavelengths of a few decimetres.

(Frequencies are related to wavelengths through the well-known equation
v = fλ (v : velocity ; f : frequency; λ : wavelength)).

The highest-pitched components will not be very audible, as they are several kHz in frequency, and so around a centimetre in length. Since they are therefore smaller than the mouth opening, they are quite directional.

Underwater, since sound speeds are much higher than in air (typically about five times faster), the wavelength of a wave of a given frequency is proportionately large. This means that, unless sources are many metres across, all audible-frequency underwater sound waves tend to radiate in all directions.

In many applications, it is desirable to generate directional sound beams, for communication or for pulse-echo detection techniques. Narrow beams reduce off-axis noise levels, travel great distances with little energy loss, produce few confusing side-echoes and are more suitable for transmitting sensitive information.

However, in all media, higher-frequency sound waves are absorbed over shorter distances than lower ones, and for this and other reasons one often wishes to transmit relatively low-frequency sounds in directional beams.

An elegant way to make a low-frequency directional sound source is the parametric array. If two sound sources generate waves which differ just a little in frequency, then waves with that difference frequency will be produced, along with others whose frequency is the sum of those of the sources. The wavelength of the difference wave can be a long as required, but it maintains the directionality of its parent waves. Parametric arrays exploit the fact that sound velocity depends on density. At high sound powers, the pressure in the compressions becomes very large, increasing density significantly and therefore speeding up the sound wave briefly; the reverse happens in the rarefactions. The effect of these velocity changes is to distort the wave from its usual sinusoidal form, as shown in Figure 1.

A non-sinusoidal wave is equivalent to a sum of component sinusoids. In the case of the parametric array, these components include the original waves, together with the sum and difference waves: the difference wave being the one of interest (Figure 2).

Mathematically, the directionality of a sound wave is defined through a directivity function, which describes the intensity (or other measure) of the sound as a function of angle from the source axis. For a parametric array, the directivity function is given at the end of this blog.

The parametric array effect was discovered by chance when, in 1951, acoustician Peter J. Westervelt was working at the Office of Naval Research in London. He noticed that an experimental superheterodyne (frequency-mixing) radio receiver was generating directional audible sound at low frequencies. It was not until 1960 that Westervelt was able properly to explain the effect, which he did at a meeting of the Acoustical Society of America, and in a published paper a few years later.

Today, parametric arrays have numerous underwater applications, and they are also used in museums and galleries for the "acoustic spotlight" system in which recorded descriptions are beamed at appropriate exhibits and can only be heard by people close to the exhibits. A parametric array is also the basis of the LRAD (Long Range Acoustic Device), used to direct painfully load sounds at, for example, Somalian pirates. Underground, sound beams from parametric arrays are used for prospecting.

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<![CDATA[Crossing sound barriers]]>Fri, 01 May 2015 05:59:16 GMThttp://soundfocus.weebly.com/blog-sculpting-sound/crossing-sound-barriers
Last week, I took part in an excellent series of workshops and events at the London Science Museum, which brought together specialists from many sound-related fields, including performers, engineers, historians, composers, experts in sound studies, and acousticians. A few years ago, I attended an EU COST (European Cooperation in Science and Technology) meeting about soundscaping, with a similarly wide range of specialisms.

Both events were very successful in terms of exchanging information and experiences from a range of perspectives, and the work of many of the attendees benefitted. However, one thing I learned from both meetings is just how chasm-like the distinctions between different approaches can be. As soon as any topic is explained in any depth, technical terms proliferate, and many are properly understood only within the field. Worse, the same term may have very different meanings in different disciplines (interference, post-processing, mitigation, noise, reluctance, sharpness ...).

But there are other, more general distinctions too, between analytic, reductive approaches and holistic, synthesizing ones, between fields in which the need for political perspective and motivation is taken for granted and those in which such any such thing is deplored, between criticism and calls for action, between art and science.

None of this is surprising, nor is it unique to the field of sound; television, for example, is the subject of a similarly vast and partially mutually incomprehensible range of approaches. But in sound, this "out of scope" issue really matters, because there are numerous problems which many specialists could potentially work together to solve, and some problems which cannot be solved by any one approach alone.

Soundscaping is one such example. Faced with the challenge of modifying a small urban park surrounded by busy roads, one might start by gathering a meeting of people with relevant interests. Who should be there? Town planners and local residents, clearly. And environmental noise experts. And sound artists. And then, how about social psychologists? Anthropologists? Architects? Landscape gardeners? Legal experts? Local politicians? Government bodies? Local historians? The Highways Agency, DEFRA, the AA.... and so on.

The problem here is not really that of bridge-building; in my (albeit limited) experience, experts in different fields do trust the expertise of those in others and there seems a general appreciation that even very unfamiliar approaches have their own unique advantages, and should be taken seriously. In most cases too there is a lot of pleasure to be had in explaining the fundamentals of one's subject or of learning the basics of a new one. The difficulty is in actually working together across fields.

Yet surely true collaboration across barriers must be possible? After all, grappling with sound - however one does it - is rarely an esoteric pursuit in the sense that, say, string theory is. So no approach to it is likely to be impenetrable to someone from another field. Secondly, the point and purpose of any practitioner is usually easy both to grasp and to empathise with : it may not be clear why proving the Riemann hypothesis or reaching Pluto matters, but we can all appreciate the hazards of noise and the benefits of music.

Two experiences may have some bearing on possible solutions. Part of the COST meeting was a series of visits to locations with noise problems, but where interventions could be made: a very small green area with a fantastic view (in the heart of a busy estate), ancient monuments in a leafy setting (in the middle of a gyratory system), a school playground (surrounded  by residential  buildings). We were asked to discuss and propose ways in which the soundscape of each amenity could be improved. And, at the Science Museum, we were provided with sets of instructions and some electronic components and tasked with building and playing a musical instrument. In both cases, the challenge of a well-defined yet broad task, with a set timescale and specific set of deliverables, led immediately to enthusiastic collaboration, augmentation of approaches and formulation of novel solutions.

Perhaps these successes happened because the problems which any particular sound specialists wishes to solve are usually recognised as important by others too. Secondly, those problems can usually be explained quite precisely in non-technical language. And thirdly it is usually clear to all when a satisfactory solution has been reached. This trio of characteristics is absent from many other fields, like sociology, advanced mathematics, economics, education, political theory, robotics, clothes design, genetic engineering...

If there's a moral it might be: if you're planning a cross-disciplinary meeting in the field of sound, build a problem-solving activity into its heart.
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<![CDATA[Call back yesterday...]]>Fri, 13 Feb 2015 10:48:41 GMThttp://soundfocus.weebly.com/blog-sculpting-sound/call-back-yesterday
... bid time return,

so said the Earl of Salisbury (according to Shakespeare), and so says the Engineering and Physical Sciences Research Council (EPSRC) - which has recently announced its trio of "Engineering Challenges", for which groups of researchers may apply for funding (details at
http://www.epsrc.ac.uk/funding/calls/towardengnmrcc/)

One of these Challenges is "Future Cities: engineering approaches that restore the balance between engineered and natural systems" which sounds at once interesting, laudable and vague and so exactly the kind of thing to stir the imagination and think up ways to improve our cities.

Though one might not initially think of one of the goals of an acoustician as being the restoration of balance in this way, perhaps in fact that is precisely what many of us are trying to do, at least in the fields of noise, room acoustics and underwater sound.

The soundscape concept (roughly, the aural equivalent to a landscape, but applicable indoors as well at out) is a useful one with which to explore this idea, by asking: what soundscapes do we wish to inhabit? If you're reading this on a train carriage shared with a group of football supporters or museum-bound school children, under a flight path or next door to a drum-kit, "a silent one" might be your response. Actually living in silence, however would quickly lose its charm (as anyone who has spent any time in an anechoic chamber will probably agree).

Maybe living or working in "a natural soundscape" is more appealing - birdsong, the wind through trees, waves on the shore, the falling of the rain. If those were all there was to hear though, most of us might be pining for music before long. And, when switching on the washing machine, vacuum cleaner, car, or lawn-mower, silence would be a rather uncomfortable result.

So perhaps, one might say that the ideal soundscape would be one that balances sounds which natural with some that are ... well, "engineered" is actually the best word I can find here. However, given that most of us probably are not entirely content with the soundscapes we work or travel in, and many of us feel the same way about those we live in, a bit of rebalancing could be welcome.

Initially the word "restore" seems an odd one for EPSRC to use in discussing the requirements for future cities but actually it may be an appropriate one for our soundscape ideals. Imagine the sound-world you might really like to live and work in and it might well be based on memories : maybe a quieter home with fewer machines, a cellular office, older music, fewer planes? Or perhaps a workspace where rather the hum of computers and the whisper of air conditioning, some outdoor sound drifted in through open windows?

Short of inventing a time machine or signing up for one of those BBC series where people pretend to live in the 1940s, this may seem an unhelpful conclusion. But looking closer at this idea of a remembered or otherwise idealised soundscape does lead to some concrete ideas as to what a soundscape with a "restored" balance between nature and engineering might mean.

For a start, a larger contribution by natural sounds would probably be welcome. Perhaps (as in my last blog) acoustic barriers with a vegetation layer might help, especially if the plants attracted birds and bees. Maybe the addition of recorded or synthesised natural sounds could help too - if carefully chosen, subtly used and properly trialled. Air conditioning with a slight temporal variation of shifted tonality might hint at waves on shores or wind in forests.  Work has been done already (by Brigade electronic in particular) on warning systems which use "shushing" sounds rather than sirens or buzzers – and arguably such sounds are acceptable in part because they are more like natural ones. Recorded bird song in shopping centres is not new, though has often failed in the past through insufficient discussion with visitors before and during its installation. And of course, the rise of the electric car - which all agree must make sounds for safety reasons - gives us a whole new acoustic canvas which we have great freedom to colour with whatever sound seem best. Work is certainly required here to decide what sounds, and to what if any extent they might have natural elements, would be best - not just for individual cars, but for busy traffic too.

Whether any of these ideas are good, the time seems right to consider what kind of sound world we want - in part because many of these we have are becoming increasingly unsatisfactory. Many efforts have been and are being made to quieten our world, but in some areas, little further progress is possible - such in the areas of aircraft noise and neighbour noise. In such cases, it is certainly worth asking whether adding sounds can help (which is the essence of the whole soundscape approach to improving our acoustic environment).

This is a good time to be having these discussion for another reason: thanks to advances in solar power and other energy-harvesting systems, in computer technology and in the use of MEMS (Micro-Electronic Mechanical Systems) to build tiny acoustic devices, we now have highly effective, discreet, reliable, autonomous and adaptable sound-generating systems which would allow us to add whatever sounds we want, wherever we want them.

Before any such additions are made, it would be essential to bring together experts in the many disparate fields involved: psychologists, sociologists, noise consultants, engineers, acousticians, sound artists, architects and local authorities, and also second to find out, though well-designed and substantial social surveys, just what kind of balance between natural and engineered sounds people would really like to restore.


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<![CDATA[Crowd soundings?]]>Fri, 30 Jan 2015 15:44:25 GMThttp://soundfocus.weebly.com/blog-sculpting-sound/crowd-soundings
I have a confession to make: I've just bought my first smart phone. And I do now understand why, before I did so, some people were prone to gasping with astonishment when they found that I just had a boring old mobile, and wondered how I was able to leave home without one, let alone make a phone call. 

In fact, I'd already been forced to embrace a key aspect of smart telephonics - I've been no stranger to apps since buying a new laptop, but the advantage of being able to press a virtual button-with-symbol rather than an icon-with-label escaped me till I understood that I'd only scraped the surface. There's a galaxy of the things available on my Galaxy.  

I soon discovered that one of these things is a sound level meter. Two minutes later, I'd found lots more - most of which are free - and the ones I tried gave sensible readings and had some useful features.

On the face of it, the sudden availability of sound level meters to everyone with a smart phone allows a revolution in acoustic data gathering - and a very timely revolution too, now that soundmapping has become a key concept in noise abatement (thanks in large part to the European Noise Directive).

In fact, given that the starting-point of that directive was the reduction in personal noise exposure, a sound level meter you carry with you - a personal noise dosimeter, in other words - is actually even more useful than a sound map.

However, though there have been some projects in which people have used their phones to chart noise levels, it's not an idea that has really taken off. I've no idea how many people use calorie-counting apps, or symptom-checking or healthy lifestyle ones, but I bet it's a lot more than use sound level meter ones, even those on the phones of people who work, live or play in noisy places. Nor -as far as I know - is there any system of collection of level data from owners. Of course, there are plenty of technical reasons to prefer an actual sound level meter to an appy one. The MEMS microphones that all mobile phones used are not designed for measurement, and their frequency range is limited. If you want to know your noise exposure, your measurements should be taken near your ears, not your pockets. And phone microphones are designed to be directional, too.

On the other hand... you don't need an accurate measurement to determine that noise exposure is too high. With potentially millions of readings, sophisticated statistical analysis, modelling and data pruning can be conducted. For detecting changes over time, or season, or place, the low quality of the instruments is more than offset by their similarities and constancies. And compared to the cost of an actual sound level meter - to say nothing of that of the accompanying acoustician or extensive training course required to use it properly, the price tag of £0.00 looks like good value to me.

Maybe all that's needed is a little dot-connecting: like a system in which people permit their phones to measure noise levels and transmit them to a central database, in exchange for an (automated) regular report about the noise levels they are exposed to, and what that means in terms of health impacts. The data thus collected could be used to generate live and detailed sound maps of ... well, practically everywhere on Earth where people gather. And, over time, the evolution of the soundscapes of those areas would be charted too. A bit of publicity and some centralised data processing is all that's required. And of course, an app.

What do you reckon? Unworkable? Unnecessary? Possible? Let's do it? Any comments much appreciated... 

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<![CDATA[Sound maps by crowd science?]]>Fri, 30 Jan 2015 15:16:38 GMThttp://soundfocus.weebly.com/blog-sculpting-sound/sound-maps-by-crowd-scienceI have a confession to make: I've just bought my first smart phone. And I do now understand why, before I did so, some people were prone to gasping with astonishment when they found that I just had a boring old mobile, and wondered how I was able to leave home without one, let alone make a phone call (actually I bet there's a much smarter phrase than "make a phone call" these days). 

In fact, I'd already been forced to embrace a key aspect of smart telephonics - I've been no stranger to apps since buying a new laptop, but the advantage of being able to press a virtual button-with-symbol rather than an icon-with-label escaped me till I understood that I'd only scraped the surface. There's a galaxy of the things available on my phone.  

I soon discovered that one of these things is a sound level meter. Two minutes later, I'd found lots more - most of which are free - and the ones I tried gave sensible readings and had some useful features.

On the face of it, the sudden availability of sound level meters to everyone with a smart phone allows a revolution in acoustic data gathering - and a very timely revolution too, now that soundmapping has become a key concept in noise abatement (thanks in large part to the European Noise Directive).

In fact, given that the starting-point of the directive was the reduction in personal noise exposure, a sound level meter you carry with you - a personal noise dosemeter, in other words - is actually even more useful than a sound map.

However, though there have been some projects in which people have used their phones to chart noise levels, it's not an idea that has really taken off. I've no idea how many people use calorie-counting apps, or symptom-checking or healthy lifestyle ones, but I bet it's a lot more than use sound level meter ones, even those on the phones of people who work, live or play in noisy places. Nor -as far as I know - is there any system of collection of level data from owners.

Of course, there are plenty of technical reasons to prefer an actual sound level meter to an appy one. The MEMS microphones phones used are not designed for measurement, and the frequency range is limited. If you want to know your noise exposure, your measurements should be taken near your ears, not your pockets. And phone microphones are directional, too.

On the other hand... you don't need an accurate measurement to determine that noise exposure is too high. With potentially millions of readings, sophisticated statistical analysis and data pruning can be conducted. For detecting changes over time, or season, or place, the low quality of the instruments is more than offset by their similarities and constancies. And compared to the cost of an actual sound level meter - to say nothing of that of the accompanyinng acoustician or extensive training course required to use it properly, the price tage of £0.00 looks like good value to me.

Maybe all that's needed is a little dot-connecting: like a system in which people permit their phones to measure noise levels and transmit them to a central database, in exchange for an (automated) regular report about the noise levels they are exposed to, and what that means in terms of health impacts. The data thus collected could be used to generate live and detailed sound maps of ... well, practically everywhere on Earth where people gather. And, over time, the evolution of the soundscapes of those areas would be charted too. A bit of publicity and some centralised data processing is all that's required. And of course, an app. 








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<![CDATA[Beyond the barrier]]>Thu, 08 Jan 2015 18:57:24 GMThttp://soundfocus.weebly.com/blog-sculpting-sound/beyond-the-barrier
Sound barriers are not regarded with a great deal of affection. In fact, they're not much regarded at all; perhaps not surprising, given that their greatest goal is to ensure that those who benefit notice neither the barrier nor the noise sources it hides. The majority are basic workmanlike structures, built according to tried and trusted principles: their sound reduction effects depend primarily on density and dimension; at least 10 kg under each square metre of surface, and high enough to hide the sound source, will reduce the noise level by about 5 dB. Adding extra height provides further reductions of about 1.5 dB per additional metre.

Just like every other kind of noise reducing element, introducing noise barriers at the earliest design stage of a noisy new project is far superior to retrofitting them - but in reality, at least in the UK, most barriers are sticking-plasters rather than structural elements. Thsi is becaise., by the tiem nayone (anyone in pawer, that is) got round to the realsiation that roads, railways and airports, though lovely in many ways, are none too pleasant to listen to, most such noise sources had been built. The widespread introdcution of nosu ebarriers to UK roads and airports was triggered largeoy by the efforts of pioneering nosue campaigner (and architect ogf the Noise Abatement Spcoity) in eth 1960s. Hence their usually uninspiring appearence.

Of course, like every other kind of technology, there is a select group who love sound barriers. When I located a book called "Environmental Noise Barriers" recently, it was far from the drab monochrome tome I was expecting - packed with great photography and artwork as well as equations and diagrams, it was clearly a labour of love.

And maybe we should all learn to love them - or at least to consider their potential: in principle they offer a canvas for great  artwork (non-distracting), for the collection of energy (solar, acoustic, vibratory), for noise measurement (and hence sound mapping), for teh absorbtion of chemcial polluanst from engines exhuasts, for illumination or for planting.

Such are the complexities of the link between objetive sound levels and the annoyance they cause, using noise barriers for more than just blocking sound wheels can allow them tod o a better job: while planting vegetation on the quiet side of barriers will not attenuate nise significant unless the layer is many metres deep (100 metres of forest reduces noise by about 20 dB), a natural-looking screen can sigificantly reduce the number of people whom the remaining noise annoys, having the same effect as a 5 dB reduction according to one study. Similarly, how much more wlecome woudl a nsoie barrier at the bootom of your garden if it was used to power your house or clean your air.

In addition to changing teh way barriers look, one coudl also modify teh way theywork. the main mechanism for soudn reduction in traditional barriers is reflection, but new materials could be used tobuild an absorbtiev barrier (and the captural energy used to generate electrciity, for example). Or, if the noise has characteristci frequncies., layer sof Helmholt resonators could be used.

With HS2 (probably) on its way, new roads being planned, and old infrastuctures crumbling, maybe now is the time to rethink our barriers and even - who knows? - to love them.

















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