page_title: Temporal envelope and fine structure
section_title: Definition
hierarchical_section_title: Temporal envelope and fine structure / Definition
caption_attribution_description: English: Diagram showing the three levels of temporal envelope and temporal fine structure of a signal processed by the auditory system
context_page_description: Temporal envelope and temporal fine structure are changes in the amplitude and
  frequency of sound perceived by humans over time. These temporal changes are responsible for several aspects of auditory perception, including loudness, pitch and timbre perception and spatial hearing.
  Complex sounds such as speech or music are decomposed by the peripheral auditory system of humans into narrow frequency bands. The resulting narrow-band signals convey information at different time scales ranging from less than one millisecond to hundreds of milliseconds. A dichotomy between slow "temporal envelope" cues and faster "temporal fine structure" cues has been proposed to study several aspects of auditory perception at two distinct time scales in each frequency band. Over the last decades, a wealth of psychophysical, electrophysiological and computational studies based on this envelope/fine-structure dichotomy have examined the role of these temporal cues in sound identification and communication, how these temporal cues are processed by the peripheral and central auditory system, and the effects of aging and cochlear damage on temporal auditory processing.
context_section_description: Notions of temporal envelope and temporal fine structure may have different meanings in many studies. An important distinction to make is between the physical (i.e., acoustical) and the biological (or perceptual) description of these ENV and TFS cues.
  Any sound whose frequency components cover a narrow range (called a narrowband signal) can be considered as an envelope (ENVₚ, where p denotes the physical signal) superimposed on a more rapidly oscillating carrier, the temporal fine structure (TFSₚ).
  Many sounds in everyday life, including speech and music, are broadband; the frequency components spread over a wide range and there is no well-defined way to represent the signal in terms of ENVₚ and TFSₚ. However, in a normally functioning cochlea, complex broadband signals are decomposed by the filtering on the basilar membrane (BM) within the cochlea into a series of narrowband signals. Therefore, the waveform at each place on the BM can be considered as an envelope (ENVBM) superimposed on a more rapidly oscillating carrier, the temporal fine structure (TFSBM). The ENVBM and TFSBM depend on the place along the BM. At the apical end, which is tuned to low (audio) frequencies, ENVBM and TFSBM vary relatively slowly with time, while at the basal end, which is tuned to high frequencies, both ENVBM and TFSBM vary more rapidly with time.
  Both ENVBM and TFSBM are represented in the time patterns of action potentials in the auditory nerve these are denoted ENVₙ and TFSₙ. TFSₙ is represented most prominently in neurons tuned to low frequencies, while ENVₙ is represented most prominently in neurons tuned to high (audio) frequencies. For a broadband signal, it is not possible to manipulate TFSₚ without affecting ENVBM and ENVₙ, and it is not possible to manipulate ENVₚ without affecting TFSBM and TFSₙ.
caption: Schematic representation of the three levels of temporal envelope (ENV) and temporal fine structure (TFS) cues conveyed by a band-limited signal processed by the peripheral auditory system.
exif: {"Image Orientation": "Horizontal (normal)"}