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inverting, and so on) that transforms the sound parameter data in some appropriate manner. For example, the command expression:
would map over each of the events referenced by * and set the amp parameter of each Event to a randomly selected value between .1 and .6. In many cases, a value for a particular sound parameter can only be calculated by first knowing its current value, or the current value of other parameter. To reference the value of a sound parameter, the name of the parameter must be preceded by a $. For example, $index means 'the value of the index parameter in the currently mapped object'. As a non-trivial example of how this might be used, the command expression:
scale examp[::2] index (interpolation $index 1 2 10 .5)
would scale every other event in the Examp container by multiplying the value of each index parameter by an interpolated coefficient ranging between 2 and .5 as the current index value ranges between 1 and 10. The effect of this command is therefore to boost small index values and to reduce larger ones according to linear interpolation using the x,y coordinates {1,2 10,.5}.
The most powerful sound parameter command in Stella is its general purpose Map utility which may be used for both querying sound data as well as editing it. When data is queried, information is returned in a table displaying the query, the number of times it was true, and the results of the query operation. Query operations are useful for statistical analysis of compositional material. For example, suppose a composer has used an Generator named Gong to algorithmically create 1000 gong-like tones whose rhythms, fm-indices and frequencies were calculated using some sort of random distribution. But the composer now wishes to know the total rhythmic space of the gong sounds whose fundamental frequencies lie between fs4 and fs5. Since randomness was used to generate values for the frequency and rhythm parameters, this information can only be gained by examining each of the 1000 elements, checking the frequency and summing the rhythm value when appropriate. The Map command allows a composer to do this easily, as a single query operation:
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