Drag and drop a wav file onto the waveform display on the center bottom. There is a function that indefinitely runs grains at variable rate intervals, selectable by clicking the 'Constant' tab on the top left.

Additionally there is a function to playback the grains in a linear rate by clicking 'Linear' tab on the top left. This function let's you specify the speed to playback the individual grains, as well as the size of each.

The synth is based on the tutorials of Peter Batchelor which I highly recommend for learning more about Max programming and digital synthesis techniques.

The source code can be downloaded on my github.