Within his writings on spectromorphology Smalley describes gesture as a sound, which is brought to life by an agent (human) through a physical activity (applying energy to a sounding body) to produce spectromorphological qualities (Smalley 1997: 111) He refers to this process as the energy-motion trajectory. As gesture is related to an agent we as listeners try to decode the source cause based on the spectromorphological qualities attributed to a specific sound. However, often within electroacoustic music there is no perceivable source causebecause of manipulation undertaken by a composer on a specific sound. Smalley refers to this process as Gestural Surrogacy and outlines four types of surrogacy within music: first-order surrogacy, second-order surrogacy, third-order surrogacy and remote surrogacy (Smalley 1997: 112).
Sounds of a first-order surrogacy can include recordings of sonic activity that are not intended for musical use, as they are not able to attain the status of an instrument (Smalley 1997: 112). However, it is imperative that listeners are able to apprehend the source of the sound in order for it to be considered a first-order surrogate.
Second-order surrogacy deals with sounds that are instrumental by nature, where "recognisable performance skills" are used to "develop an extensive registral articulatory play" (Smalley 1997: 112). Simulations of such sounds are also considered as second-order surrogates because of the perception of the listener.
Third-order surrogacy refers to gestures that have a source case that is either "inferred or imaged" (Smalley 1997: 112). This could be because the material might not be know to the listener, or that the spectromorphological qualities might behave in an unexpected way.
Smalley uses the term "gestural vestiges" to describe how a gesture might be perceived to be a remote surrogate (Smalley 1997: 112). For a gesture to be considered a remote surrogate it will have no perceivable or indeed inferred source cause or agent.
SMALLEY, D. (1997) Spectromorphology: explaining sound-shapes. Organised Sound, 2(2), pp. 107-126.