Those are System Exclusive messages used only by Roland devices (or by GS compatible devices, i.e., devices that emulate the Roland SoundCanvas). You will find an explanation in the manual of your device.

Anyway, there is a tutorial by Eddit Lotter.

Thanks Clemens Ladisch, I didn't know they were used only by Roland... I found what I was looking for in a combination of Eddies page and the manual but it is so darn hard to figure something out, when you're not familiar with it and so darn obvious once you do.