Frankly, I dunno. I recognized it during the time I added hum to some of the sound fonts I own, to be compatible with the DIYino boards. I was wondering how come the sound quality was inferior to how they sounded like in original on the PC. I despaired...until Jakesoft introduced his app to append hum automatically. For the first time I had sounds unaltered, and they sounded all of a sudden clear and crisp.
So here is my case: Jake's app makes a magnificient job of adding hum to the sounds. It always adds one hum length, which is perfect. However some sound fonts have exteremly long hum sounds, some justified because the whole is unique, some just repeats the same sequence over and over again. These latter I would like to shorted to about 3-5 secs, with which I could convert the sound fonts to be compatible with my board which comes with SPI flash. With optimized lenght I could squeeze in up to 3 sound fonts, which is my goal. I already have a working build with 3, but so far I only have the xxx resamples version from Audacity.
Of course if there is any way to get rid of this annoying feature, so much better.