Communication Acoustics

An Introduction to Speech, Audio and Psychoacoustics

Ville Pulkki, Matti Karjalainen

• Publisher: Wiley
• Year: 2015
• ISBN:
  9781118866559
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Signals & Signal Processing
• Index: Technology & Engineering

In communication acoustics, the communication channel consists of a sound source, a channel (acoustic and/or electric) and finally the receiver: the human auditory system, a complex and intricate system that shapes the way sound is heard. Thus, when developing techniques in communication acoustics, such as in speech, audio and aided hearing, it is important to understand the time–frequency–space resolution of hearing.

This book facilitates the reader's understanding and development of speech and audio techniques based on our knowledge of the auditory perceptual mechanisms by introducing the physical, signal-processing and psychophysical background to communication acoustics. It then provides a detailed explanation of sound technologies where a human listener is involved, including audio and speech techniques, sound quality measurement, hearing aids and audiology.

Key features:

• Explains perceptually-based audio: the authors take a detailed but accessible engineering perspective on sound and hearing with a focus on the human place in the audio communications signal chain, from psychoacoustics and audiology to optimizing digital signal processing for human listening.
• Presents a wide overview of speech, from the human production of speech sounds and basics of phonetics to major speech technologies, recognition and synthesis of speech and methods for speech quality evaluation.
• Includes MATLAB examples that serve as an excellent basis for the reader's own investigations into communication acoustics interaction schemes which intuitively combine touch, vision and voice for lifelike interactions.

1
How to Study and Develop Communication Acoustics

The rest of this book describes facts, theories, and models of communication by sound and voice – both human and machine. The objective of basic research in this field is to better understand how we communicate, while the engineering goal is to develop and use technology to make this communication more versatile and powerful. In both cases, the challenge is to understand a variety of topics and to solve problems by approaching them from several points of view.

1.1 Domains of Knowledge

Different phenomena in nature, living organisms, society, and technology obey different laws and exhibit different properties and thus require different scientific concepts to study them. Even when phenomena appear similar, a detailed interpretation of specific laws to be applied may be quite different. That is why we can have (and actually must use) different domains of knowledge.

In some problems it is enough to have a look at just one aspect of reality (one domain), but with complicated multidisciplinary problems, many domains must be mastered. In complex cases, such as the topic of this book, we are forced to know at least the basics of several domains of knowledge in order to master the field properly. Some of these domains are more basic, while some are important from a methodological point of view in research and others from an application or a practical point of view. For a modern approach to sound and voice communications, we deal in this book with the following domains of knowledge:

• Acoustics and the fundamentals of physical sound deal with the interaction between physical objects that form the basis for sound and vibration phenomena. This domain answers questions on how sound is generated by sound sources, how it propagates or is absorbed, how it behaves in a closed space such as a room, auditorium, or a concert hall, and so on.
• Signal processing comprises the theories and techniques on how signals carrying information are generated, transmitted, analysed, or transformed by humans, in nature, or using technical devices. In this domain, the basic physical details are of less importance, and abstraction from physical interaction to (typically) one-directional input–output causal relations is emphasized.
• Speech and audio are concerned with the fundamental characteristics of spoken and audio signals, and the specific techniques for communication with them. Spoken language and speech or language technology are of great importance, although in this book we will discuss them only briefly. Music, music acoustics, and music technology also belong to this category.
• Physiology and the psychophysics (psychoacoustics) of hearing study how our auditory system works both from a physiological and a functional point of view. This domain includes several important subtopics, one of which is spatial hearing, which deals with how we localize sound sources and perceive sound environments.
• Mathematics and computer science are the sciences that provide the general methodologies required to get the formal understanding necessary to model and realize complex communication processes.
• Engineering applications is the field that utilizes a wide variety of techniques for sound and voice communications. This includes traditional acoustics design, control of noise, speech technology (speech analysis, synthesis, coding, recognition), audio technology (recording, production, reproduction), multimedia sound (integration of sound with other modalities) virtual acoustics, and technical audiology for helping with hearing problems, etc.

Research in these and related topics is often scattered and separated. One of the main objectives of this book is to provide the reader with a broad overview, without digging too deeply into details of any subtopic, since there are more specialized books and publications available for that purpose. Before starting this journey of facts, theories, and models, a characterization of related research methodologies and how they evolve is given.

1.2 Methodology of Research and Development

Scientific and engineering knowledge of communication processes has developed over the last hundreds, even thousands, of years. First there were beliefs that sounded rational, but a closer investigation found them to be false or only partially true. Some early thinkers and experimenters, such as Pythagoras, turned out to be very successful and influential (Hunt, 1992). Pythagoras studied the behavior of strings and understood the inverse relation between pitch and string length in ancient Greece during the sixth century B.C. Related to the harmony (consonance) of sounds, he assumed that the whole universe followed simple number rules of harmony. In the 1700s experimental studies in, and mathematical theories of, the physical sciences improved our understanding on how, for example, sound propagates in the air. Sound sources were better understood, and Hermann von Helmholtz had a modern view on the functioning of the human ear (von Helmholtz, 1954) more than a century ago. Since then, electronic and digital communications have forced scientists and engineers to learn more deeply the secrets of signals and the information conveyed by them.

There are three basic ways a scientist or engineer may acquire knowledge about a system or process, such as communication by sound and voice:

• Experimentation with, say, concrete physical or psychophysical, systems. This has been the standard approach used by scientists and engineers, augmented by practical or theoretical thinking. Concrete experimentation involves a large number of details, which makes seeing general laws behind the multitude of phenomena difficult, but on the other hand it helps to verify that the thinking is not too far from reality.
• Modelling of an object or phenomenon by means of constructing another kind of system that simulates the original phenomenon or object but is easier to experiment with. The first modelling techniques were based on constructing concrete, physical objects as models. The modern approach, using computer-based simulation, has expanded the capability of modelling techniques dramatically.
• Theory formation is a conceptual approach to formulating general principles inherent in a specific field of research. A theory has higher generality and potentially the widest applicability compared to experimentation and modelling techniques. On the other hand, very general theories are hard to apply to complex and specific cases in practice; they rather help and direct the thinking process.

Many forms of scientific and engineering methodologies can be formulated as different combinations of the three approaches. Figure 1.1 characterizes these as levels of the abstraction process as well as realizing abstractions back towards practice. Abstraction means getting rid of details that are not essential for modelling or understanding a specific object or principle, and concretization (realization) is the opposite process of adding details in order to approach reality or practical construction of a system.

Figure 1.1 Abstraction and realization processes in research through experimentation, modelling, and theory formation.

Recently, in this age of computers being applied everywhere, the three approaches of experimentation, modelling, and theory formation have started to merge and integrate. Experiments are often carried out using computational models before the final validation against practice. The difference between theory and computational models is also becoming less distinctive, since advanced computer models, including artificial intelligence and logic programming, may enable high-level theoretical inference.

Progress in research and practical applications is based on continuous iteration between the levels of abstraction, aiming at improved models and theories that better meet the challenges of reality.

1.3 Systems Approach to Modelling

A systems approach to studying a specific object means abstraction and modelling which is based on the finding that very many (if not all) objects in reality exhibit some general properties that can be described using systemic concepts. The target may be of a physical origin, a society of living beings, or a human-made technical artefact, and yet some general concepts may apply to all of them.

Figure 1.2 shows a very simple diagram and Figure 1.3 a more complex one that may be understood as systemic descriptions of something, not specific to any domain of knowledge until so related. Based on such descriptions, one may compile a list of concepts representing systemic aspects. The reader may wish to propose another set of systemic concepts, or disagree with the authors about the usefulness of such concepts. The list presented here is not intended as a basis of a ‘general systems theory’, rather it orients the reader to the way the authors have tried to...

Table of contents

• Cover
• Title page
• Copyright page
• Dedication page
• About the Authors
• Preface
• Preface to the Unfinished Manuscript of the Book
• Introduction
• 1 How to Study and Develop Communication Acoustics
• 2 Physics of Sound
• 3 Signal Processing and Signals
• 4 Electroacoustics and Responses of Audio Systems
• 5 Human Voice
• 6 Musical Instruments and Sound Synthesis
• 7 Physiology and Anatomy of Hearing
• 8 The Approach and Methodology of Psychoacoustics
• 9 Basic Function of Hearing
• 10 Basic Psychoacoustic Quantities
• 11 Further Analysis in Hearing
• 12 Spatial Hearing
• 13 Auditory Modelling
• 14 Sound Reproduction
• 15 Time–Frequency-domain Processing and Coding of Audio
• 16 Speech Technologies
• 17 Sound Quality
• 18 Other Audio Applications
• 19 Technical Audiology
• Index
• End User License Agreement