We’ve seen that sounds of unspecified duration are normally represented by a triangle or “wedge” shape.
For sounds of specified duration, the wedge symbol is modified, keeping the same outline while reducing the symbol to one vertical and one horizontal line, like a rotated letter T. As with the wedge symbol, the vertical line at the left represents the onset of the sound. The horizontal line—the “stem” of the T—is extended to the point where the sound ends, thus specifying the duration of the sound.
Normally, equal units of horizontal length will represent equal units of time, e.g. 1cm = 1 second, or 1cm = 1 beat. Thus, if one sound of specified duration lasts twice as long as another, the symbol for the first sound will be twice as long as that for the second.
Symbols representing sounds of either specified or unspecified duration can be positioned along a layer line according to their timing, always remembering that the left-hand edge of a symbol represents the onset of the sound. As the rotated T symbol representing sounds of specified duration also includes a horizontal line, both lines of that symbol are drawn thicker than the layer line to distinguish them from it.
When pitch is to be unspecified, the symbols for sounds are placed immediately above or below the layer line. By default, symbols are placed above the line.
However, the distinction between above and below can also be used to convey information, such as the division of strokes between a pair of drums (see Specifying other information where duration is unspecified).
When pitch is to be specified, the symbols are normally placed on a line representing that pitch (see Specified pitch).
The basic symbols for sounds of specified and unspecified duration can be varied and combined with other symbols to specify many other aspects of sound.
Next: Specified onset timing