Software-Based Acoustical Measurements

438 Pages·2017·10.2 MB·English

by  Federico Miyara (auth.)

Modern Acoustics and Signal Processing
Federico Miyara
Software-Based
Acoustical
Measurements
Modern Acoustics and Signal Processing
Editor-in-chief
William M. Hartmann, East Lansing, USA
Editorial Board
Yoichi Ando, Kobe, Japan
Whitlow W.L. Au, Kane’ohe, USA
Arthur B. Baggeroer, Cambridge, USA
Neville H. Fletcher, Canberra, Australia
Christopher R. Fuller, Blacksburg, USA
William A. Kuperman, La Jolla, USA
Joanne L. Miller, Boston, USA
Alexandra I. Tolstoy, McLean, USA
Series Preface for Modern Acoustics and Signal Processing
Inthepopularmind,theterm“acoustics”referstothepropertiesofaroomorother
environment—the acoustics of a room are good or the acoustics are bad. But as
understood in the professional acoustical societies of the world, such as the highly
influentialAcousticalSocietyofAmerica,theconceptofacousticsismuchbroader.
Ofcourse,itisconcernedwiththeacousticalpropertiesofconcerthalls,classrooms,
offices,andfactories—atopicgenerallyknownasarchitecturalacoustics,butitalso
is concerned with vibrations and waves too high or too low to be audible.
Acousticiansemployultrasoundinprobingthepropertiesofmaterials,orinmedicine
for imaging, diagnosis, therapy, and surgery. Acoustics includes infrasound—the
winddrivenmotionsofskyscrapers,thevibrationsoftheearth,andthemacroscopic
dynamicsofthesun.
Acoustics studies the interaction of waves with structures, from the detection of
submarines in the sea to the buffeting of spacecraft. The scope of acoustics ranges
from the electronic recording of rock and roll and the control of noise in our
environments to the inhomogeneous distribution of matter in the cosmos.
Acoustics extendstotheproductionandreceptionofspeech andtothesongs of
humans and animals. It is in music, from the generation of sounds by musical
instruments to the emotional response of listeners. Along this path, acoustics
encounters the complex processing in the auditory nervous system, its anatomy,
genetics, and physiology—perception and behavior of living things.
Acousticsisapracticalscience,andmodernacousticsissotightlycoupledtodigital
signalprocessingthatthetwofieldshavebecomeinseparable.Signalprocessingisnot
only an indispensable tool for synthesis and analysis, it informs many of our most
fundamentalmodelsforhowacousticalcommunicationsystemswork.
Given the importance of acoustics to modern science, industry, and human
welfare Springer presents this series of scientific literature, entitled Modern
AcousticsandSignalProcessing.Thisseriesofmonographsandreferencebooksis
intended to cover all areas of today’s acoustics as an interdisciplinary field. We
expect that scientists, engineers, and graduate students will find the books in this
series useful in their research, teaching and studies.
William M. Hartmann
Series Editor-in-Chief
More information about this series at http://www.springer.com/series/3754
Federico Miyara
Software-Based Acoustical
Measurements
123
Federico Miyara
Laboratorio deAcústica y Electroacústica
Universidad NacionaldeRosario
Rosario
Argentina
ISSN 2364-4915 ISSN 2364-4923 (electronic)
ModernAcoustics andSignal Processing
ISBN978-3-319-55870-7 ISBN978-3-319-55871-4 (eBook)
DOI 10.1007/978-3-319-55871-4
LibraryofCongressControlNumber:2017935823
ThisisanupdatedandexpandedEnglish-languageversionoftheSpanish-languageedition:Mediciones
acústicas basadas en software by Federico Miyara, Asociación de Acústicos Argentinos, © Federico
Miyara2013.AllRightsReserved.
©SpringerInternationalPublishingAG2017
Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpart
of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations,
recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission
orinformationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar
methodologynowknownorhereafterdeveloped.
The use of general descriptive names, registered names, trademarks, service marks, etc. in this
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To María Victoria, Francisco and Andrés
Preface
Acoustic metrology has long presented the problem that sound measuring instru-
ments are very expensive. This is due to two types of components: the transducer,
i.e.,themicrophone,andtheelectronicsrequiredtoperformsignalconditioningand
processing (filtering, analysis, comparisons) and display the results.
At the beginning, both the microphone and the electronics were intrinsically
expensive.Themicrophone,becauseitwasasophisticatedelectromechanicdevice
which required a complex manufacturing process and high-quality materials to
ensure robustness, flat frequency response, low distortion, and stability over time.
The electronics, because of the need of highly trained labor as well as expensive
high-quality components.
Nowadays, instrumentation grade microphones are still expensive, but the cost
of electronics has dropped several orders of magnitude. So one would expect that
acoustical instrumentation prices had dropped as well. However, they tend to rise!
For instance, a decade ago it was possible to purchase a first-brand sound level
meter for about $2000. Today, the cheapest instrument that replaces that one is
twiceasexpensive,evenconsideringthattheinternationalinflationofthedollarhas
been only 30 % during the same time span, and the manufacturing cost has been
further reduced by offshoring in countries like China and by the replacement of
many discrete components by a small count of custom integrated circuits. In con-
trast,thecomputerindustryexhibitstheoppositetrend:thepriceofwhatatagiven
timeisconsideredtobeastate-of-the-artcomputernotonlydoesnotincreasebutis
actually falling below the dollar inflation.
Measurementinstrumentmanufacturerstrytoimplythatthepricerisepaysfora
lot of exciting new features that are now possible through the use of sophisticated
microprocessing units. However, the real cost of hardware and software is a very
smallfractionoftheretailprice.Moreover,theyhaveadoptedacommercialpolicy
from the software industry, which is to license different software (firmware)
modulesthatrunonasinglehardwareplatform.Fromthemanufacturerstandpoint,
this reduces even further the manufacturing cost since the same hardware can be
used to provide the functionality of several instruments as well as the promise of
futureupdates(whichcertainlyarenotcheap).Insomecases,firmwaremodulesare
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preinstalled and all that is needed is to buy the code that unlocks the desired
function.
In this scenario, the idea to exploit the potential of personal computers arises.
Any user with some programming experience has at their fingertips the possibility
to replace or emulate the signal processing that takes place inside a typical
advanced soundlevelmeteroranalyzer.Asinequanonprerequisiteistohavethe
signal available in digital format. This is accomplished by means of an external
digital audio recorder which records the calibrated audio output signal that almost
anysoundlevelmeterprovides.Oncedigitized,thesignalmaybesubjecttomany
differentprocesses,fromcomputinganyoftheclassicparametersandindicatorsto
any possibility deserving to be investigated that our imagination can think of.
The traditional measuring paradigm is, hence, starting to change. Instead of
recording a reading as an abstract translation of some property of a given phe-
nomenonwithnopossibilityoffurtherverification,werecordtheveryobjecttobe
measured. It is true that the original object is a sound field with complex spatial,
temporal, and spectral distribution, and that by capturing it by means of a single
microphone a severe abstraction process has been already performed. But it is the
same abstraction process that the sound level meter carries out prior to the actual
measurement!
The proposal put forward in this book is to examine traditional measurement
processes and to present alternative approaches to be implemented using mathe-
matical software running on a general purpose personal computer. Compatibility
withInternationalStandardsinthefieldofacousticalmeasurementsisalsoanalyzed
to ensure that the algorithms to be used comply with relevant standards. Several
examples of parameters that are usually absent even in sophisticated commercial
instruments are also given. In all cases, the proposal involves the minimum hard-
wareandsoftwareinvestment,whichiswhyalltheexamplesusefree,opensource,
and multiplatform software.
While every effort has been made to render the book reasonably self-contained,
some prerequisites should be fulfilled to profit the most from its reading: (1) A
fluent working knowledge of algebra and calculus of several variables, including
thecomplexvariableandthebasicsofdifferentialequations.(2)Afairacquaintance
with the theory of signals and systems, including the Laplace and Fourier trans-
forms, the concept of spectrum and basic filter theory. (3) At least an elementary
knowledge of Acoustics. (4) A good command of computers. (5) Some program-
mingexperience.(6)Agraspofelementaryprobabilityandstatistics(thoughthere
is an appendix covering the basics).
Chapter 1 introduces the general concepts of acoustical measurements, such as
equivalent levels, time and frequency weighting, statistical descriptors, and spec-
trum analysis, with emphasis on theprocess ofmeasurementstabilization. Chapter
2 covers the most distinct aspect of measurement quality: uncertainty. While
measurement uncertainty is extensively treated in many books and standards, the
particular case of acoustical measurements is often neglected or presented in a
fragmentary way. An in-depth treatment is provided here. This chapter may be
skippedinafirstreadingwithoutlossofcontinuity.Chapter3coversmanyaspects
Preface ix
of digital recording, from sampling and analog/digital/analog conversion to audio
fileformats,recordingmedia,andlong-term preservation.Thischaptercanalsobe
skippedorpresented inadifferent order ifstartingearliertoprogramalgorithms is
the priority and the reader has a practical acquaintance with digital recording.
Chapter 4 is an introduction to digital audio editing with special reference to its
applications to measurement postprocessing. Chapter 5 covers several aspects of
transducers that are relevant to their use in a measurement system, such as fre-
quency response and directivity. Chapter 6 introduces digital signal processing,
covering the main standard techniques such as convolution, discrete systems, dif-
ference equations, Z transforms, and stability. This chapter can be skipped if the
reader is already acquainted with the basic theory of digital signal processing.
Chapters 7 and 8 cover specific techniques and algorithms used in acoustical
measurements. Finally, Chap. 9 presents the test methods to be applied to digital
recorders to ensure the hardware complies with the relevant standards.
Each chapter includes a problem set in which the main ideas are applied to
practicalsituations.Inseveralproblems,additional oradvancedmethodsrelatedto
the subject of the chapter are introduced.
Finally, the book contains sixteen appendices covering supplementary material,
derivations, and basic theory or examples.
Becauseofspacerestrictions,itisnotpossibletoincludeherebutshortexcerpts
of some programs implementing the general ideas that are studied herein. That is
why full-length examples are to be included in the Web site of the Acoustics and
Electroacoustics Laboratory of the National University of Rosario. They will be
available for download from http://www.fceia.unr.edu.ar/acustica/measurements.
Rosario, Argentina Federico Miyara
March 2016
Acknowledgements
Special thanks to my wife, María Victoria Gómez, and to my sons, Francisco and
Andrés, for their permanent support to my crazy projects. To my parents, José
Miyara and Julia Elvira Verdeja, my gratitude for the best legacy they could have
given me: the intellectual stimulus and the awareness of the importance of
knowledge, two necessary conditions so that someday I could write this book.
Thankstomy fellows,colleagues, scholars, andfriendsfrom the Noise Group and
the Acoustics and Electroacoustics Laboratory (National University of Rosario):
Susana Cabanellas, Vivian Pasch, Marta Yanitelli, Patricia Mosconi, Juan Carlos
Rall,JorgeVazquez,JoanPuigdomènech,PabloMiechi,DavidGiardini,Fernando
Marengo Rodriguez, Ernesto Accolti, Ezequiel Mignini, Federico Bergero, Mauro
Treffiló,EzequielRaynaudo,andLucianoBoggino,withwhomIhavesharedmany
metrological adventures, including the development of measurement software, all
of which have been the basis for the methods discussed herein. Thanks to Marina
Fernández de Luco for her frequent help with Statistics. I am also indebted to the
Agencia Nacional de Promoción Científica y Tecnológica, a national research
programfundingorganizationthatsupportedseveralresearchprojectsinvolvingthe
development of techniques that inspired parts of this book. My gratitude to the
AcousticalSocietyofArgentina(AsociacióndeAcústicosArgentinos),AdAA,and
particularly to its president, Nilda Vechiatti, for giving me the opportunity to
publish the original Spanish version of this book under its imprint. Finally, thanks
to my publishing editor at Springer, Sara Kate Heukerott, for her support in the
processofgettingthisbookpublishedandtothereviewerWilliamHartman,whose
comments have helped me to give the manuscript a final polish, and to the
Production Editor Govardhana Manoharan for the final typesetting of the
manuscript.
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