Compared to noise, which is unwanted sound, a signal is any sound or message which is meant to be listened to, measured or stored.
In soundscape studies, sound signals are always treated in relation to their ambient or keynote context, since they complement that context in the same way figure and ground are related in visual perception. Thus, a study of signals also reveals important information about the overall sound environment.
Sound signals may be studied in any of the following ways:
on the basis of their acoustic characteristics, which may represent a recognized code or other pattern pertaining to their use; subjectively, by their individually perceived meanings; historically, according to their evolution within a given social context; comparatively, by type and function in different cultures or periods; symbolically, according to their connotative and associative meanings.
Sound signals are important in the way in which they regulate the life of a community and reflect its character. Those of historic importance may be termed soundmarks. The area over which a sound signal may be heard is its profile or acoustic space, which may be regarded as its sphere of influence. In modern urban environments, many community signals are disappearing both physically and acoustically with rising ambient noise levels.
(Source - adapted and summarised from Barry Truax - Handbook for Acoustic Ecology CD-ROM Edition. Cambridge Street Publishing, 1999 - CSR-CDR 9901)