[fxtentacle]

You won't need that much source code to verify their claims.

Their central improvement is that they limit the generation of high frequencies by ReLU through a upsample-ReLU-filter-downsample sequence.

Their theoretical section explains quite well why high frequencies can be proven mathematically to cause issues. And their practical implementation using filters to cut those off is very straightforward.

If someone tells you "The microphone recording had 50Hz noise so I used a filter to remove it", that's pretty much good enough for someone with experience in the field to replicate their results. This is the equivalent in AI. They uncovered a simple basic issue that everyone else overlooked, but once you know it, it seems obvious in retrospect.