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Textural density is the relative amount and registral placement of simultaneously sounding pitch material, throughout the hearing range or within a specific pitch area. It is the amount and placement of pitch material in the composite musical texture (the overall sound of the piece of music) in relation to defined boundaries.
With textural density, sound sources are assigned (or perceived as being within) a certain pitch area, within the entire audible range (or range used within a certain piece of music). Thus, certain pitch areas will have more activity than other pitch areas; certain sound sources will be present only in certain pitch areas, and other sources present only in other pitch areas; some sources may share pitch areas, and cause more activity to be present in those portions of the range; some pitch areas may be void of activity. Many possible variations exist.
Textural density is a component of pitch-level relationships, that is directly related to traditional concerns of orchestration. Textural density is a much more specific concern in recorded music because it is controllable in very fine increments. Traditional orchestration was concerned, basically, with the selection of instruments, and with the placement of the musical parts (performed by the assigned instruments) against one another.
With the controls of signal processing (especially equalization), sound synthesis and multi-track recording, the registral placement of sound sources and their interaction with the other sound sources take on many more dimensions. Each sound source occupies a pitch area; the acoustic energy within the pitch area of a timbre's spectrum is distributed in ways that are unique to each sound source. The spectrum of each sound source is an individual textural density, and the textural density of the overall program (or musical texture) is the composite of all of the simultaneous pitch information from all sound sources.
Sound sources, and musical ideas, are often delineated by the pitch area they occupy within the composite textural density. Sound sources are more easily perceived as being separate entities and individual ideas, when they occupy their own pitch area in the composite, textural density of the musical texture. This area can be large or quite small, and still be effective.
Sounds that do not have well-defined pitch quality, occupy a pitch area. These types of sound are noise-like, in that they cannot be perceived as being at a specific pitch. Such sounds may, however, have unique pitch characteristics.
Many sounds cannot be assigned a specific pitch, yet have a number of frequencies that dominate their spectrum. Cymbals and drums easily fall into this category. Cymbals are easily perceived as sounding higher- or lower-than one another. Yet a specific pitch cannot be assigned to the sound source.
We perceive these sounds as occupying a pitch area. We perceive a pitch-type quality in relation to the registral placement of the area in which the highest concentration of pitch information (at the highest amplitude level) is present in the sound, and in relation to the relative density (closeness of the spacing of pitch levels) of the pitch information (spectral components). We are able to identify the approximate area of pitches in which the concentration of spectral energy occurs, and are thus able to relate that area to other sounds.
Pitch areas are defined as the range spanned by the lowest and highest dominant frequencies around the area of the spectral activity. This range is called the bandwidth of the pitch area. Many sounds will have several pitch areas where concentrated amounts of spectral energy is occurring, with one range dominating and others less prominent. The size of the bandwidth and the density of spectral information (the number of frequencies within the bandwidth and the spacing of those frequencies) define the sound quality of the pitch area.
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