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If the sound material being evaluated is not in a musical context, increments based on the second must be used. It will be common to use increments based on the second in the evaluation of timbre relationships (including sound quality and environmental characteristics). While conceptualizing the pulse of mm=60 (or an integer or a multiple thereof) will provide some reference to the listener in making time judgments without a metric grid, this activity may not always be appropriate. It may distort the listener's perception of the material, and the reference may be unstable, as the listener's attention will rightly be focused elsewhere.
A stopwatch will often assist in evaluating larger time units (to the tenths of seconds). The ability to judge time relationships can be developed. Practicing the following exercise will, over time, allow the reader to refine their skills in accurately making time judgments.
Exercise 8-1. Time Judgement Development Exercise.
With practice, the listener will develop the ability to make accurate time judgments of a few milliseconds within the context of known, recognizable sound sources and materials. This skill will be invaluable in many of the advanced sound evaluation tasks regularly performed by audio professionals.
The time unit used in the line graph will be that which is most appropriate for the sound event. The time increment selected must allow the graph to depict the sound event accurately; the smallest perceivable change in the components of sound being analyzed must be readily apparent, and yet as much material as possible should be contained on a single graph.
The components of sound to be plotted and the boundaries of states and activities of those components are next determined. In the initial two stages of the sound evaluation process, the listener determines those components of the sound event that provide it with its unique character. These components of the sound event will be those selected for analysis through plotting on the line graph.
The component of the sound event to be evaluated will be placed on the vertical (Y) axis of the line graph. Through the second step of the sound evaluation process (above), the listener will determine the maximum and minimum values found in each of the components of sound. These maximum and minimum values will be slightly exceeded in establishing the upper and lower boundaries of the Y axis (depicting the component).
Exceeding the perceived limits of the values of the components allows for errors that may have been made during initial judgments of the boundaries, and allows for greater visual clarity of the graph. Boundaries should be exceeded by five to fifteen percent, depending on context of the sound event and the space available on the line graph.
Next, the minimum changes of activity and levels are determined. Through "Step 3" of the sound evaluation process (above), the listener will determine the smallest increment of value for the components of the sound event.
This smallest increment of value will serve as the reference in determining the correct division of the Y axis. It is necessary for the Y axis to be divided to allow the smallest value of the component of sound to be clearly represented on the vertical axis of the graph, as was the above concern with the division of the X (time) axis of the graph.
The division of the vertical axis must allow the graph to depict the sound event accurately. The smallest significant change in the components of sound being evaluated must be immediately understood by the reader of the graph, and yet the vertical axis must not occupy so much space as to distort the material. The reader of the graph must be able to identify the overall shape of the activity, as well as the small details of the activity of the component the graph represents. A balance between limitations of space, and clarity of presentation of the materials must always be sought.
It is not always desirable for each component of the sound event to have its own line graph. Many times several components of a sound event can be included on the same graph, and plotted against the same time line. Multi-tier graphs allow several components to be represented against the same time line. With the advantage that their characteristics will be more easily interrelated during the final formulation of observations.
The vertical (Y) axis of the line graph is divided into segments. Each segment is dedicated to a different component of the sound event. Each segment will have its own boundaries and increments.
The plotting of a number of components of sound against the same time line not only makes efficient use of space on the graph, it allows a number of the characteristics of the sound event (perhaps the entire sound event) to be viewed simultaneously. By placing a number of the components of the sound event against the same time line, it is possible to give a more complete and a more easily understood representation of the sound event. The person reading the graph will be able to extract information more quickly from a "multi-tier" graph that from a series of individual graphs. In addition, the plotting of various components of the sound event against the same time line allows for the comparison of the states and activities of the various components of the sound event in ways that would be more difficult (if not nearly impossible) were these components separated.
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Figure 8-2. Multi-Tier Graph (click on image for full size)
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Multi-tier graphs of a specific nature will be used for certain advanced evaluation processes. In those cases, the graphs will always appear in a predetermined format.
Multiple sound sources within the same component of the sound event must also be graphed. It is quite common for more-than-one aspect within a component of the sound event to be taking place at any one time (such as the sound of harmonics and overtones within the spectrum of a sound). This activity would require a separate tier of a multi-tier graph for each sound source in each component of the sound event being evaluated. The line graph would quickly become large and unclear.
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