Decisions about whether to specify sound sources and pitch determined the way we set up the “layers” of our manuscript paper (see Sound sources; Unspecified pitch). Next we need to decide how to represent the actual sounds by using appropriate graphic shapes. A graphic shape that represents a sound will be called a “symbol.”
What kind of symbol to use depends whether we want to specify the duration of the sound or not.
“Duration” means how long the sound continues. Since sounds are sometimes separated by silences, duration is a separate question from the question of when each sound begins, which we will call “onset timing.”
Staff notation tends to blur this distinction, but Global Notation needs to keep it clear. That is because onset timing is nearly always musically significant and worth specifying in the score, while duration may or may not be. Global Notation does not force you to specify duration (or anything else) when it is not relevant to your purposes.
In singing or playing a bowed or wind instrument, the sounds are “sustainable” in that the performer has the ability to sustain a sound and control when it ends. For sustainable sounds, it usually matters how long the sound goes on.
The sounds of most drums and xylophones, on the other hand, are “impulsive”- generated by a momentary “impulse” such as hitting the instrument - and die away rapidly without the player’s control. For impulsive sounds it can be misleading to specify a definite duration, or to suggest that one note lasts longer than another.
Thus, it is usually helpful to specify duration for sustainable sounds but not for impulsive sounds. However, there may sometimes be reasons for doing otherwise (see Further considerations re: specifying duration).
According to whether duration is to be specified or not, Global Notation distinguishes between two basic categories of symbol:
Unspecified duration: discrete symbols of fixed shape.
Specified duration: extendable symbols whose length varies according to duration.
The form that the symbols take is governed by the convention that time is represented as flowing from left to right. Thus, the left-hand edge of a symbol represents the beginning or “onset” of the sound.
With impulsive sounds, the onset is normally the loudest part, after which the sound dies away. In a computer-generated waveform graph, such a sound looks roughly like a triangle, tall at the left and diminishing to a point at the right. In global notation, this shape is stylised to form the default symbol for a sound of unspecified duration: a triangle or “wedge” shape with a vertical left-hand edge. The wedge shape makes the onset of the sound visually prominent - appropriately so, since the onset is usually the most rhythmically significant moment in a sound, even when it is not the loudest.
While a wave-form graph might show wedges of different proportions according to the varying rates of decay of different impulsive sounds, in the notation the wedge shape is standardised as an equilateral triangle, remaining the same for every stroke, to indicate that no differentiation of durations is intended.
The wedge symbol is normally filled in solid black, but for more rapid writing by hand, it can be drawn in outline only. (Similar adaptations can be made for many other aspects of Global Notation: see Writing by hand).
While the wedge shape is the default symbol for sounds of unspecified duration, various other shapes can be used to convey further information about the sounds (see Specifying other information where duration is unspecified).
When duration is to be specified, the wedge is modified into an extendable symbol.