You can specify materials on your own textures using one of the following 12-character-prefixes inside custom materials file:
VENTTEXTURE_ (Resilient metal/brass sounds)DIRTTEXTURE_ (Dry dirt/sand/gravel sounds)GRATETEXTURE (Reverbing metal grate sounds)METALTEXTURE (Solid metal/steel sounds)SLOSHTEXTURE (Mud sounds)TILETEXTURE_ (Squeeky plastic tile sounds)WOODTEXTURE_ (Wooden planks sounds)COMPTEXTURE_ (Fragile metal/plastic/electronics sounds (hits only))GLASSTEXTURE (Glass sounds (hits only))FLESHTEXTURE (Flesh sounds; sort of like trampling through a muddy puddle)SNOWTEXTURE_ (Sound of crunching snow when walking over)
Custom materials file can be selected in map properties. | 
