Called by the signal chain to update this UGen's ouput data. Subclassses of UGen should implement the UGen's DSP perform routine here. In
general this involves grabbing data from UGen.bufIn and putting data
into UGen.bufOut in some way. UGen.bufIn and UGen.bufOut are 2D arrays of floats of the form float[numChannels][bufferSize]. The length of the buffers is given by
UGen.bufferSize, and the number of channels of the input and output buffers are given by UGen.ins and UGen.outs respectively.