It isn't really a type of voice. In English, when we have a sore throat we sometimes describe our throats as being "scratchy." A "scratchy voice," is one that sounds like people sometimes do if they have a sore throat/heavy cold. The term "scratchy," might also be referring to being like the noise that a scratched record would produce. Records were what we had before Compact Discs. They were made of vinyl. The record player had a needle that would be lowered onto grooves on the record and this is how the sound was transmitted. Sometimes, something would go wrong and the needle would land outside of one of the grooves. When this happened the flat surface of the record would be scratched and, when you tried to listen to the record a noise would be heard that sounded like static.