Darvishi, A.

Guggiana, V.

Rauterberg, G.W.M.

English

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 Analysis and synthesis of environmental soundsCitation for published version (APA):Guggiana, V., Darvishi, A., & Rauterberg, G. W. M. (1995). Analysis and synthesis of environmental sounds.(Technical report; Vol. 95.12). Swiss Federal Institute of Technology.Document status and date:Published: 01/01/1995Document Version:Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the version of the article upon submission and before peer-review. There can beimportant differences between the submitted version and the official published version of record. Peopleinterested in the research are advised to contact the author for the final version of the publication, or visit theDOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and pagenumbers.Link to publicationGeneral rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            • Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            • You may not further distribute the material or use it for any profit-making activity or commercial gain            • You may freely distribute the URL identifying the publication in the public portal.If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, pleasefollow below link for the End User Agreement:www.tue.nl/taverneTake down policyIf you believe that this document breaches copyright please contact us at:openaccess@tue.nlproviding details and we will investigate your claim.Download date: 04. Oct. 2023Analysis and Synthesis ofEnvironmental SoundsAuthors :Valentin Guggiana, Alireza Darvishi, Eugen Munteanu, Helmut SchauerDepartment of Computer Science (IfI), University of Zürich,Winterthurerstrasse 190, CH-8057 Zürich, SwitzerlandMasoud MotavalliSwiss Federal Laboratories for Material Testing and Research (EMPA)Uberlandstrasse 129, CH-8600 Dubendorf, SwitzerlandMatthias RauterbergUsability Laboratory, Work and Organizational Psychology UnitSwiss Federal Institute of Technology (ETH), Nelkenstrasse 11, CH-8092 Zürich,Swi tzer landTel: +41-1-632 7082, email: rauterberg@rzvax.ethz.ch2A b s t r a c tThis technical report describes steps toward synthesis of environmental soundslike impact, bouncing, breaking, scraping and other impact sounds. The firstsection shows by means of knowledge engineering the investigation of possiblemethodologies and techniques for developing and describing environmentalsounds in the industry. The second section describes various laboratoryexperiments which have been carried out in a anechoic room, impacting beamsand plates of different materials. This is followed by physical modelling of theinteracting objects which are involved in the sound generation. Thesynthetically generated and recorded sounds were used for comparison and forderiving data for further analysis. Hence physical modelling of sounds could beexamined through data analysis and adjusted if necessary. Some developedalgorithms for analysing impact sounds as well as some developed algorithms forsound synthesis are introduced later.Psycho acoustical comparison tests will soon be carried out, and will allow us totest the quality of generated sounds and to gain more knowledge about theperception of environmental sounds in general.Knowledge EngineeringIn order to define relevant parameters and possibilities for describingenvironmental sounds, we were concentrating on the following knowledgeengineering techniques:- interviewing experts- accompanying sound designers during their work- analysing sounds in film documentsIn terv i ewing  Exper t sIn the last years many automobile and household technology companies haveestablished new departments for modelling and designing sounds, i.e. soundengineering departments. They are using modern workstations for analysing,manipulating and generating sounds. In order to achieve certain sound effectswith cars (e.g. sporty, engine power), different types of sounds inside theautomobile and the sounds of wheels and motor are being analysed andmanipulated. Thus, the latest knowledge of psycho acoustics is being applied.The main idea of doing these interviews was to explore concepts and find possibleparallels between sound design in those domains and human-computerinterfaces. Listed below are the most important companies,  Universitydepartments and their contact persons, that we visited:- BMW (cars), München: Mr. Tonhauser (Department of Sound Engineering)- VW (cars), Wolfsburg: Dr. Müller (Department of Acoustics)- Cortex (Acoustic Workstations), Regensburg: Prof. Dr. Zollner- Head Acoustics (Sonometers), Herzogenrath: Mr. Schmeisser- TU München (Institute for Human-Computer Communication): Prof. Dr. Fastel- University of Oldenburg (Physics Department ): Dr. Reinert WeberObserving Sound Designers During Their WorkAt the Sound Exhibition in Basel (Switzerland) in summer 1994 two famous sounddesigners demonstrated their methods and techniques in sound simulation forfilm production. We interviewed them both about their tools and techniques forsound synchronisation in films and radio plays.3Analysing Existing Film DocumentsWe watched and analysed a film from a German television channel about sounddesign techniques and synchronisation. The film introduces the job of a sounddesigner in detail.R e s u l t sOur investigations and observations were not very relevant to our researchproject. Formal descriptions of everyday sounds by attributes or typicaladjectives are very difficult for sound designers. The design of sounds in theautomobile and household technology industry are both very different fromsound design aspects in our research project.Sound engineering in those domains aims mainly at manipulating sounds inorder to achieve specific sound effects. It does not aim at defining methods for aformal representation of sound. In contrast, the scope of our research project isto define new algorithms for the automatic generation of environmental sounds.We also try to describe environmental sounds in the German language from alinguistic point of view.Exper imentsAt the EMPA Dübendorf (Switzerland) we have carried out experiments in ananechoic room with beams and plates made of various materials and withdifferent shapes. Various spheres were dropped from different heights ontoplates and beams and the resulting sounds were recorded on a DAT tape. Thedigital recordings have an excellent quality for further processing.Through various combinations 252 different sounds were generated for analysisand later comparison:3 heights . 7 spheres . 6 materials . (plate + beam) = 252 soundsFigure 1 illustrates schematically the equipment for our laboratory experiments.Table 1 and 2 list the properties of the objects involved, which build the basis forour calculated sounds.hmv0Ha, LbplateorbeamFigure 1: laboratory equipmentn a m e g s1 s2 s3 s4 s5 s6m a t e r i a l g la s s s t ee l s t ee l s t ee l s t ee l s t ee l s t ee ldiameter [mm] 14.1 7.5 8.0 9.0 10.0 12.0 14.04mass [g] 3.65 1.72 2.09 2.98 4.07 7.02 11.16Table 1: spheresm a t e r i a l p l a t ed i a m e t e r[mm]b e a md i a m e t e r[mm]d e n s i t y[kg /m3 ]po i s son -coe f f i c i en te las t ic i ty[GPa]a l u m i n i u m 3.98 3.98 2700 0.33 71.0g la s s 7.94 7.94 2300 0.24 62.0wood 8.06 8.06 720 0.30 5.0Plexiglas 3.80 3.90 1180 0.30 3.3PVC 6.00 6.12 1390 0.38 3.9s tee l 2.96 2.96 7700 0.28 195.0Table 2: plates and beamsPhysical ModellingThe ApproachA qualitative analysis of impact sounds shows that they decrease in intensityexponentially. Theoretical considerations and real sound analysis lead us to asystem of damped natural modes of vibration with various initial amplitudes.However, this approach only applies to certain materials, those which arehomogeneous and non dispersive. A formal description for the approach is :u = A0 ⋅ e−δ ⋅t ⋅ ei⋅ω ⋅t∑ u d i sp l acemen tA0 initial amplitudeδ d a m p i n gω e i g e n - f r q u e n c yt t i m eE i g e n - F r e q u e n c i e sThe eigen-frequencies (natural frequencies) of each object depend on itsmaterial properties and its geometric shape. With respect to the above mentionedconditions, the elasticity modulus and the Poisson coefficient are encounteredwithin the formula. The formula allows a direct description of simple geometricforms like plates and beams. Complex geometric forms however, requireintensive numeric calculations. In any case, the formula remains scalable,which means that changing one instance results in a linear change in theoverall result. The next formula for a clamped beam shows this:f n =n2πhL2E3ρf n n-th eigen-frequencyE elas t ic i tyρ d e n s i t yL l e n g t hh d i a m e t e rn number of eigen-frequencyInitial Amplitude  / ExcitationResearch by Koller [K], based on previous work by Zener [Z] investigates themotion of impact force. Analyses of that force lead to the spectrum of excitednatural frequencies. The impact time is too short, so that results range within thespectral uncertainty :∆ω ⋅ ∆t ≥ 1, with ∆t ≅ 40µs , thus ∆ω ≅ 25kHz5The spectral range which can be perceived by humans, resides between 20 Hzand 20 kHz; human sensitivity decreases with higher age. Hence, the influence ofthe impact force on the initial spectrum can be ignored.eF_____F maxttimeFigure 2: Impact forceNevertheless, the exact location where the impact force strikes has a greatinfluence on initial amplitudes. Obviously, an impact force applied on a node of anatural frequency does not excite the respective modes of vibration. On thecontrary, when the sphere strikes right in the peak of an eigen frequency wave,this mode will be fully excited.0 L An (x) = A0 ⋅ sinn ⋅ π ⋅ xLn = 3 n = 2 n = 1Figure 3: Excitation localisationThe above explanations consider only relative amplitudes of differentfrequencies among each other. Even though it is possible to calculate theabsolute amplitudes as well, what we really hear is also dependent on the distancefrom sound source. Therefore, we consider only the relative initial amplitudesand their evolution related to the impact point.D a m p i n gOne can distinguish two kinds of damping for real sounds: intrinsic and systemd a m p i n g .The intrinsic damping results from the material's internal friction. It is possibleto calculate intrinsic damping by the complex elasticity modulus for variousmaterials [W]:δ = ω ⋅ tan φ M = Μ(1 + i ⋅ tan φ )δ d a m p i n gω f r e q u e n c yφ phase between strain and stressM complex elasticity modulusM real part of elasticity modulus7Typical events where intrinsic damping is much more important than systemdamping are: vibrating strings, tuning-forks and bells.System damping is very important when additional (boundary) conditions existand the whole system undergoes damping. Window panes, doors and tables aretypical examples from daily life. A precise mathematical calculation of systemdamping is impossible, so experimented values and empirical formulas are calledf o r .A n a l y s i sThe results of our experiments supply the parameter set (A0 , δ , ω ), which arerelevant for our approach. In the following three paragraphs we will describethe applied algorithms.Eigen  Frequenc iesFourier transformation is applied to the whole length of the sound in order toobtain the best frequency resolution. This results in a loss of time resolution, butit does not matter, as time is of no particular importance for this demand. Sound´sduration of course depends on the damping of different frequencies. In ourmeasurements the duration fluctuates between 15 ms and 30 ms. Therefore, thefrequency resolution ranges between 6 Hz and 63 Hz. By precise segregation ofdifferent frequencies it is even possible to have a higher resolution by using themethod of the smallest square. One can demonstrate this approach nicely, bygenerating synthetic signals. As the human ear is very sensitive to comparingthe frequencies of different sounds, we can easily justify an additional effort forthis approximation.Initial Amplitude / ExcitationThe initial amplitude of a sound can be calculated from a short fragment from thebeginning of sound. After having determined a frequency, it is easy to calculatethe initial amplitude precisely. However it is important to notice that throughtransformation a time interval is integrated. Accordingly, the amplitude is notrelated to a specific time but to a time interval. Hence, the correction factor k ,can be calculated for At=κ  A∆t as follows:κ = ∆te−δ ⋅tdt0∆t∫ ⇒ κ = δ ⋅ ∆t1 − e−δ ⋅∆t∆ttAFigure 4: Initial amplitudeD a m p i n gParameter δ of damping can be calculated from two amplitudes at different times.The precision can be increased, the more succesive amplitudes per time arecons idered .The sound is divided in multiple parts, which may overlap. Through Fouriertransformation it is possible to calculate a designated amplitude for anyfrequency which relates to a specific time interval. This amplitude A(t) is8corrected by the same factor which was mentioned above in order to have theamplitude for a certain time. δ is derived as follows:A(t) = A0 ⋅ e−δ ⋅t ⇒ δ =− ln A(t)A0tWe have divided the signals into 32 parts and each part has 512 samples in orderto minimise the time overlay of parts and yet have enough frequency resolution.These values describe the overall damping. Unfortunately, a distinction betweenintrinsic and system damping is not possible as the derived information fromanalysed data does not contain any information about the original materials.Limitations /  ProblemsThe investigation showed that such analysis offers good results if eigen-frequencies are separated clearly enough. This is the case for homogeneousmaterials like metals, glass and synthetic materials. Unfortunately this is not thecase for wood or similar materials which consist mainly of fibres, especially ifthese fibres are not strictly directed. In order to model these materials we have totake into account their dispersive characteristics as well as the differentbehaviour along axis.S y n t h e s i sReal time behaviour plays a mayor role in sound synthesis. For user-interfaceapplications synthesised sounds need to be made in real time. The two techniquesof sound synthesis, which are described below, can be also efficientlyimplemented in silicon to exploit the parallelism of the algorithms.Addit ive  Synthes i sThe technique of additive synthesis reflects our approach for which the formulawas already given above. It is possible to implement an efficient and fastalgorithm by using the Euler formula. Real time behaviour is only limited by theamount of generated frequencies. The simplicity of this technique has manyadvantages as well as disadvantages. The advantage lies in the controllability ofthe results, which always fulfil expectations, but its power is quite restricted.However, this technique is well suited for testing and generating syntheticsounds .Filter BankIn contrast to the additive synthesis this technique is an extractive one. Withsome white noise as input, only some frequency bandwidth is able to passthrough the filter. Some parallel filters, so-called filter banks are used. Thetransfer characteristic of this filter is derived from material properties and thegeometry of sound producing objects. The advantages of this technique are thatthe transfer characteristic can be controlled in time and there are a largenumber of parameter choices. It allows the generation of more complex impactsounds, like rolling, rubbing or breaking.Psycho Acoustical Tests for ComparisonDuring our project we also developed a software tool for comparison tests whichallows multiple people to listen and classify a set of sounds in random order. Byusing statistical methods we have analysed the test results, i.e. the classified9sounds to judge their quality. This helps us to decide on the suitability and theproblems of our approach.Another very useful side benefit of this project, which should not beunderestimated, is the gain of important insight about human hearing andperception capabilities.10A p p e n d i xDeveloped Tools- Sample Editor: 8, 16 and 32-bit samples; mono, stereo; can be extendeddynamica l ly :- visualisation of spectrograms (with grey levels or three dimensional relief):- numeric integration of differential equations- Fourier analysis and synthesis- generation of sounds with additive synthesis and filter bank- device independed in- and output of sounds (portability!)- automatic analysis of impact sounds11- mathematical calculation of impact sounds behind the graphical user interface:- user interface for psycho acoustical comparison test:R e f e r e n c e s[K] M. Koller, Elastischer Stoss von Kugeln auf dicke Platten, Diss. ETH Nr. 7299[Q] Quantics, Rudiments of Quantum Physics, Lévy-Leblond & Balibar, North-Hol land[W] R. Wildes, W. Richards, Recovering Material Properties from Sound, Naturalcomputation, Cambridge, MA, MIT Press, 1988[Z] C. Zener, Phys. Rev. 59, 669 (1941)

Analysis and synthesis of environmental sounds

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