When defining an Instrument, apart from constructing the space of Generators and pre-existing samples, the most important thing is to define what events the Instrument may acknowledge and how it can respond to them. We distinguish three kinds of events or parameters: low-level parameters, timbre space parameters and high-level parameters.
The first kind of parameters address low level features in the sound like its amplitude or fundamental frequency. These parameters represent transformations can be more or less immediately applied to the sounding note using regular signal processing techniques.
The timbre space parameters are indeed a specific kind of low-level parameters that affect one of the dimensions integrated into the defined timbre space. A variation in the parameter just represents a new coordinate in the space and therefore a new interpolation between the existing samples.
Finally, the high-level parameters represent concepts that cannot be obtained by an immediate transformation or that have been assigned to one o the timbre space dimensions. Usually, a variation in a high-level parameter represents a variation in several low-level parameters and even in the timbre space coordinate. For defining those relations we need ways of describing mapping strategies.
In MetriX, for describing mappings as well as transformation there is a simple language tool that allows to define break point functions and refer to things like the number of the Generator, or the value of the parameter. We will comment more details on these matters in next section.
Finally it is interesting to note that this distinction between low-level and high-level parameters in the synthesis process is very similar to the distinction between low-level and high-level analysis parameters or descriptors that we explained in the OOCTM (see section 5.2.1).