R Murray Schafer's Classification system was first introduced in 1977 within his book the Tuning of the World. It is referenced in a chapter sharing the same name. He refers to the framework as a selection of "cataloguing systems for sound" (Schafer 1977: 134), although some of the systems are more developed than others.
The framework is split into four sections: classification of physical characteristics, classification according to referential aspects, classification according to aesthetic qualities and sound contexts.
Classification of physical characteristics
The classification of the physical characteristics of a sound deals with the salient information of a sound could be quickly notated in order to compare it with other sounds (Schafer 1977: 134). The outcome is a chart that details a sound event in its entirety. Firstly, it separates a sound event into three sections (which act as three columns within the chart): attack, body and decay. Secondly, the sound event is described by its: duration, frequency/mass, fluctuations/grain and dynamics. These four aspects act as the vertical criteria of the chart. Each of these four aspects of a sound event can be notated by using symbols or letters to denounce their state at a particular point within the event itself (either in the attack, body or decay of the sound). All but duration have the same notation that can feasibly continue throughout the entire sound (duration has to have specific notation for each of the sections in order to communicate the envelope of the sound). Finally, the estimated duration of the event is noted below.
The 'setting' of the sound is also noted as part of Schaefer's Classification system. Each sound event is described by its: distance from observer, intensity in decibels, how it is heard (distinctly, moderately, indistinctly or as ambience), texture of ambience (hi-fi, lo-fi etc.), if it is a repeated or isolated event and finally its environmental factors (reverb, echo etc.).
Classification according to referential aspects
Schafer does comment that the system used to organise the vast number of designations will be arbitrary, as no sound has objective meaning (Schafer 1977: 137). Nevertheless, he has collated a vast number of designators for referential sounds, too many to document here. However, Schafer has divided these into six categories (natural sounds, human sounds, sounds and society, mechanical sounds, quiet and silence and sounds as indicators), although it should be mentioned that Schafer has stated that these headings are arbitrary and have only been used as they seem to accommodate all descriptions he has encountered through empirical study (Schafer 1977: 137).
Classification according to aesthetic qualities
Schafer states that, reduced to its simplest form, aesthetics is concerned with the contrast between preferences of sounds; whether a person likes of dislikes a particular sound (Schafer 1997: 147). Unfortunately, because of the complexities surrounding aesthetics of sounds Schafer does not provide a simple method of noting such findings. Needless to say Schafer concludes that different cultural groups have varying attitudes to environmental sounds (Schafer 1997: 147), although Schaefer does remark that more detail is needed in this area to have a better understanding of why different groups of people react to the same sound in different ways (Schafer 1977: 148).
Finally, Schafer discusses a sounds context. This is not so much a tool, but an indication that there is a divide between the areas of acoustic, psychoacoustics, semantics and aesthetics (Schafer describes these fields as questions: what sounds are? , how they are perceived?, what they mean? and if they appeal? (Schafer 1977: 148)). He argues that a sound could share acoustic and psychoacoustic properties, but at the same time have different semantic and aesthetics connotations (Schafer 1977: 149). This is the same for the inverse.
How can it be used?
The framework acts as a means to cross examine different sounds that exist within one work. It does not fully describe a single sound event, but can be used as a quick notational method whilst listening to a work. Furthermore, it is a tool specifically devised for soundscape works (although it can of course be applied to acousmatic works as well).