Lookup Tables

The majority of the parameters in the SynthBuilder patch are assigned by lookup table note filters indexed by the incoming MIDI note. The filter indexes a linearly interpolated envelope and assigns the value to the parameter. In the STK implementation, Stephen converted the envelope breakpoints to arrays and created a linear interpolation function to index the discrete values. To verify both the envelope coordinates and indexing function, I generated a sweep of every note and plotted the debug output values. Figure 1 shows one of the lookup tables verified in this manner. While accurate, it should be noted that the coordinates listed in the arrays have only three digits of precision, while some lookup tables in the SynthBuilder patch use more than this.

Figure 1: lookup7 screen shot and plotted debug output. This particular table sets the values of the parameter DryTapAmpT60.