The purpose of this book is to j.ir€'~ 0l'l\' a new technique for the experimental investigation of the free wave model sound field of acoustics. The technique is based on the use of spherical harmonic functions of angle. Acousticians frequently encounter random sound fields whose properties may be closely modelled by use of the "free wave" field. This model field is defined by two basic statistical properties: stationarity in time, and homogeneity in space. Stationarity means that any single order statistic measured by a microphone in the field will be independent of the time at which the recording is taken, while homogeneity means that the measurement will also be independent of the mic- phone's position in the field. Furthermore, second order statistics obtained from the measurements of two microphones will depend only on the time lapse between the two recordings, and the relative spatial separation of the micro phones, and not on the microphones' absolute positions in space and time. The free wave field may also (equivalently) be pictured as a collection of plane sound waves which approach an observation position from all angles. These are the "free waves" of the title, with no correlation between waves at different angles and frequencies, although there may exist an angle-dependant plane wave density function. This is a measure of the density of sound energy arriving from different angles. The free wave field has proved to be a simple but remarkably powerful model.

This is an up-to-date reference and textbook on modern acoustics from a signal-theoretic point of view, as well as a wave-theoretic approach for students, engineers, and researchers. It provides readers the fundamental basis of acoustics and vibration science and proceeds up to recent hot topics related to acoustic transfer functions and signal analysis including a perceptual point of view. In the first part, the work uniquely introduces into the fundamentals without using heavy mathematics The following, advanced chapters deal with new and deep insights into acoustic signal analysis and investigation of room transfer functions based on the poles and zeros.

Understanding acoustics – the science of sound -- is essential for audio and communications engineers working in media technology. It is also extremely important for engineers to understand what allows a sound to be heard in the way it is, what makes speech intelligible, and how a particular sound is recognized within a multitude of sounds. Acoustic Signals and Hearing: A Time-Envelope and Phase Spectral Approach is unique in presenting the principles of sound and sound fields from the perspective of hearing, particularly through the use of speech and musical sounds. Acoustic Signals and Hearing: A Time-Envelope and Phase Spectral Approach is an ideal resource for researchers and acoustic engineers working in today's environment of media technology, and graduate students studying acoustics, audio engineering, and signal processing. - Presents unique sounds and sound fields from the perspective of hearing - Covers source-signature and sound-path analysis - Gives a reconstruction of the basics of acoustics and audio engineering via timeless topics such as linear system theory in the time and frequency domains - Uses the new envelope and phase analysis approach to signal and waveform analysis - Provides new perspectives via phase properties on ways to solve acoustical problems - Presents straightforward mathematical formulations that give familiarity to discrete expressions of sound waves - Gives a seamless and intuitive understanding — from mathematical expressions to a subjective impression of sound

Analytic methods are used to assess the impact of the two-dimensional (2-D) wave spectrum of a wind-driven sea on multistatic low-frequency surface reverberation. The problem is initially posed with a narrowband source beneath a time-dependent sea surface in an ocean that can have depth dependence and bottom layering. The propagated signal interacts with the slower moving surface waves to produce a narrowband scattered field. The small-waveheight approximation is applied to a deterministic sea surface to express the scattered field in terms of the surface elevation and the Green's function for a perfectly calm sea. Randomness is then incorporated into the surface description, and its impact is formulated for an arbitrarily placed pair of receivers. The three-dimensional (3-D) cross-spectral density (CSD) of the reverberation is reduced to a sum of baseband and sideband terms formulated as multiple mean-sea-surface integrals. The sideband result is identified as an active scattering generalization of the van Cittert-Zernike theorem from partial coherence theory. The focus is then narrowed to shallow deployment in a homogeneous ocean, and stationary-phase estimates are used to produce analytic expressions for the CSD. The zero-Doppler component and Bragg-Doppler sidebands are expressed in terms of the power spectrum of the source, the power spectrum and directionality of the surface waves, and the multistatic source/receiver geometry. Sample sideband calculations are provided to illustrate the results, and system implications are considered.

Acoustics is the science concerned with the production, control, transmission, reception, and effects of sound. Its origins began with the study of mechanical vibrations and the radiation of these vibrations through mechanical waves, and still continue today. Research was done to look into the many aspects of the fundamental physical processes involved in waves and sound and into possible applications of these processes in modern life. The study of sound waves also leads to physical principles that can be applied to the study of all waves. The broad scope of acoustics as an area of interest and endeavour can be ascribed to a variety of reasons. First, there is the ubiquitous nature of mechanical radiation, generated by natural causes and by human activity. Then, there is the existence of the sensation of hearing, of the human vocal ability, of communication via sound, along with the variety of psychological influences sound has on those who hear it. Such areas as speech, music, sound recording and reproduction.