Sound-Medium Interface

A) Acoustic: the physical transfer of energy from a vibrating object to the surrounding medium (called "acoustic radiation") and the physical transfer of acoustic energy in a medium (called "sound propagation").

B) Electroacoustic: the transfer of energy from an acoustic to an electrical form, (a process called "transduction") including various possible intermediate stages of electrical manipulation, storage and retrieval, as well as the re-conversion of the signal to an acoustic form.

C) Electromagnetic: the transfer of audio signals from transmitter to receiver via an electromagnetic wave, a process called "radio transmission".

D) Psychoacoustic: the processing of incoming sound waves by the auditory system to extract usable information for the brain, the process most commonly called "hearing".

E) Soundscape: the processing of information from the sonic environment to extract usable information for the brain which can influence human behaviour, the process most commonly called "listening".

In the original Handbook chart, a sixth term is given for the sound-medium interface in music, namely "performance", which in this context is thought of as the transfer of musical information from the composer to the listener usually via a human performer, but now also possible via loudspeaker systems. This topic is not illustrated here.

A) Acoustic: an important part of acoustics deals with the characteristics of energy-transfer (called "radiation") from a vibrating body to the surrounding medium, or from one medium to another, such as from the air to the ear canal. The emphasis is usually on the efficiency of energy transfer. In addition, we discuss some basic parameters of sound propagation through a medium; the influence of the environment on such propagation, however, will be discussed under sound-environment interaction.

B) Electroacoustic: there are three characteristic processes involved in electroacoustics, perhaps the most basic of which is the process of "transduction", that is, the conversion of acoustic energy to an equivalent electrical signal, and vice versa. Secondly, there are electrical devices which modify and manipulate such signals, and thirdly, devices which store and/or retrieve these signals. The actual devices involved are considered in a separate section of this document. In addition, digital recording and playback converts the audio signal to digital form and vice versa.

In addition, the field of electronic and computer music substitutes signal generation (sound synthesis) for the initial process of transduction from an original acoustic source. Here we present the terms which describe the essential characteristics of all of the electroacoustic transfer processes mentioned.

C) Electromagnetic: the transfer of an audio signal from a transmitter to a receiver, including its coding and decoding, via an electromagnetic wave has had a profound impact on communication in this century. The process is commonly called "radio transmission", and its details and variations are numerous. Here we present simply the basis of the process, common to all electromagnetic transmission. Keep in mind that the speed of the transmission is instantaneous, and the distances involved can be enormous.

D) Psychoacoustic: a great deal has been learned in this century about the behaviour of the human auditory system in the way it processes incoming sound waves and extracts usable information, The basic subjective concepts involved are:

a) "response" characteristics, that is, how the magnitude of the sensation caused by the stimulus relates to the physical magnitude of the stimulus;

b) the "threshold" of sensation;

c) the "just noticeable difference" in a certain parameter of the stimulus;

d) the "resolution" or "resolving power" of the system to separate simultaneous stimuli, or the way simultaneous stimuli cause a composite sensation;

e) how stimulus sensation changes over time.

E) Soundscape Studies: the basis of information transfer considered in soundscape studies is the process of listening. Listening is assumed here to include all aspects of how usable information is extracted from a complex array of environmental acoustic information, how it is classified, and how the information affects subsequent behaviour, including the listening process itself. Needless to say, not everything is known about this amazingly complex process. However, some useful terms and categories have been suggested by the research of the World Soundscape Project, many of which are related to, or at least are compatible with cognitive psychology. After some basic terms, we present those concerning:

a) categories of special sounds heard in the environment as reflected in listeners' use of the information contained in the sounds;

b) typical attitudes listeners have towards environmental sounds in recalling, accepting, rejecting, ignoring and adapting to sounds in the environment;

c) methods for documenting environmental sounds that reflect their functional importance and listeners' attitudes as mentioned.