Signals and Systems for Speech and Hearing, 2nd edition

by Stuart Rosen & Peter Howell




An introductory textbook from Brill, published in 2010.

From a review of the second edition:

'The main strength of this book is that it engenders an intuitive understanding of signals and systems ... overall the book achieves its aims and should become core reading for many students.' R.Morse (2012) ENT & Audiology News 21(5). 91.

From reviews of the first edition:

'These authors have determined to walk the fine line between simplicity and truth ... [and]  have succeeded in their goal of clarifying what can be an esoteric subject, in my opinion quite admirably.' J.F. Bartram (1993) Journal of the Acoustical Society of America 94:5, 3530.

'An essential and commendable feature of the book is that it is built around words and pictures rather than mathematical concepts. It is specifically designed for people without a mathematical and engineering background and it succeeds in providing the student with detailed and accurate knowledge of a difficult but important area in an extremely accessible form. The authors go a step further in adopting an informal style of writing which some, more used to traditional science-speak, may find surprising but in this reviewer's opinion makes the book even more readable.' J.M. Bamford (1992) European Journal of Disorders of Communication 27(4). 374-375.

What the book is about

Many people working in the speech and hearing sciences come from non-technical backgrounds, making it difficult for them to master the essential technical underpinnings of the area. The main barrier to acquiring knowledge in this area is that available textbooks nearly always assume an audience consisting of students of engineering. It is relatively difficult for the non-engineer, even with sufficient mathematical expertise, to get much out of these books. For readers without a knowledge of calculus, it is well nigh impossible.

The problem of patchy understanding of basic technical concepts is acknowledged, at least implicitly, in most books dealing with speech and hearing. Nearly all begin with an introductory chapter purporting to cover the topics explored in this book - from relatively straightforward ones like the nature of sine waves and the calculation of decibels to the much more complex ideas of Fourier analysis and synthesis. Only those who already know this material are likely to appreciate its significance, and they do not need to read such a chapter. It seemed to us that only an entire book could cover in a sensible and thorough way the main concepts required. Furthermore, although we realized that there are some students who could handle a highly mathematical text, there are many who would have no mathematical training beyond algebra and trigonometry. Therefore, we decided to try to tell the entire story in words and pictures, with only minimal mathematics.

We have attempted to provide the reader with a thorough introduction to the concepts of signals and systems analysis that play a role in the speech and hearing sciences. Few equations are used, and we have tried to maintain an informal, friendly and informative style throughout. Readers who like their technical material straight will, we hope, forgive us our little jokes. Because much of the story is told through figures, we have gone to great lengths to provide clear and truthful figures that show what the text says they do! We hope the reader will come away with a strong visual understanding of the concepts involved.

This book can be used at many levels, from the student who hasn't heard of a spectrum before, to the experienced worker who has only a fuzzy understanding of the notion of an impulse response. We have tried to keep the underlying conceptual structure of signals and systems analysis explicit, in the hope that even some readers with advanced technical training might find clarification of the basic principles.

Notable features include over 300 figures integrated closely with the text, all drawn specifically. Exercises are provided at the end of most chapters. For details of the way in which the book has been used in an introductory course primarily for audiologists, click here.

What is new

In the nearly 20 years since the book originally appeared, little has changed in the basic concepts. (Fourier's theorem is still as valid as it was first when proposed at the beginning of the 18th century!) What has changed the field immeasurably is the nearly complete replacement of analogue techniques for digital ones in the recording, manipulation, storage and transmission of signals. This has been reflected by changes throughout the book in the kind of instrumentation described. All the spectrograms in Chapter 13, dealing with aspects of speech production, have been re-made using Praat. A new section on windowing signals and spectral splatter has been added to Chapter 10. Most importantly, three chapters have been heavily revised. Chapter 11, dealing with spectrograms, has been much extended and describes the two different ways spectrograms can be constructed — through filter banks and time windowing — and the relationship between them. Chapter 14, dealing explicitly with digital signals and systems, has been expanded greatly to give concrete examples of digital systems and digital signal processing, including the notion of infinite impulse response (IIR) and finite impulse response (FIR) filters. Finally, Chapter 12 now focuses on the notion of the auditory periphery as a set of systems, showing how its function is analagous to that of making a spectrogram.

Annotated table of contents

Chapter 1 - Introduction - The relevance of studying the properties of signals and systems for work in the speech and hearing sciences; examples of signals and systems; input and output signals.

Chapter 2 - Signals in the real world - the similarity of acoustic, mechanical and electrical signals; transduction.

Chapter 3 - Introduction to signals - The specification and construction of sinusoids; the concepts of frequency, period, amplitude and phase; periodic and aperiodic sounds; measures of amplitude - peak- to-peak, rms; dB scales.

Chapter 4 - Introduction to systems - Linearity, additivity, homogeneity and time-invariance. Saturating nonlinearities. Application to middle ear and basilar membrane vibration, and to audio recording.

Chapter 5 - A preview - If we know what a linear time-invariant system does to sinusoids, we know what it will do to any signal.

Chapter 6 - The frequency response of systems - Amplitude responses as the ratio of output levels to input levels at particular frequencies. Low-pass, high-pass, band-pass and band-stop filters. The use of logarithmic axes (dB vs log Hz). The amplitude response of a cascade of systems. Application to middle ear vibrations and vocal tracts of varying shapes. Formants as resonances. Phase responses, linear and otherwise.

Chapter 7 - The frequency characterization of signals - Fourier analysis and synthesis. The amplitude and phase spectra of periodic signals: sinusoids, sawtooths, square waves, triangle waves and pulse trains. The spectra of aperiodic signals: transients and noise.

Chapter 8 - Signals through systems - Determining the output of systems to specified signals in the frequency domain, for both amplitude and phase. A sawtooth through ideal and realistic low-pass filters. Noise through a filter. Distortion.

Chapter 9 - The time characterization of systems - The notion of an impulse, and the impulse response. The relationship between the frequency response of a system and its impulse response. Determining the frequency response of a set of headphones in 3 ways: via the impulse response, a sinusoid swept in frequency, and white noise.

Chapter 10 - The relationship between the time and frequency domains - Signals short in time tend to be wide in spectrum, and vice versa. 'Windowing' signals to minimise spectral splatter. The trade-off between temporal resolution and frequency resolution in band-pass filters. The relationship between a system's impulse response and its frequency response.

Chapter 11 - Spectrograms: Practical short-term spectral analysis - Determining dynamic spectral changes; the notion of a filter bank; rectification and smoothing; short-term spectra; the use of wide- and narrow-band filters; making spectrograms in the time domain; windowing.

Chapter 12 - Applications to hearing - The measurement of frequency responses, and notions of linearity and nonlinearity in the peripheral auditory system: head and pinna, the ear canal resonance, middle ear vibration, basilar membrane motion; modelling the auditory periphery as a set of systems.

Chapter 13 - Applications to speech production - The source-filter theory of speech production and its application to vowels, diphthongs and fricatives.

Chapter 14 - Digital signals and systems - sampling and quantization; digital-to-analog and analog-to-digital conversion; aliasing; simple digital systems; infinite impulse response (IIR) and finite impulse response (FIR) filters.

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