Have you ever wanted to walk on gravel or dirt and have it sound like you are walking on gravel or dirt? Well this tutorial will tell you how to get those pesky textures to sound real. You will need a .pak explorer type program. Half-Life Model Viewer and PakScape work very well.
Open up PakScape or HLMV and open the Half-Life pak0.pak file. You should see folders with PakScape or a tree with HLMV.Open up the sound folder. You should see a text file called materials.txt. Extract it to your Half-Life\Valve\sound folder. To do this in PakScape just drag it on the area like a zip file.
In HLMV you must right click materials.txt, click extract file. Go to your valvesound folder. Type in materials.txt in the File Name field. Click save.
Now for the editing. Go ahead and open up the new file you just saved.
Notice at the top where it explains how the different letters represent different footstep sounds. All of the textures that have footstep sounds OTHER THAN the default footstep is in here, with a letter before the texture's actual name. To change the sound of a texture just simply change the letter before the name.
Ex: V DUCT_FLR01 will sound like you're crawling through a vent. Change the V to a T and that texture footstep will be a squeeky, tile like sound. Save the file, and make sure it is in the valvesound folder and your all set.
With this you can add texture sounds, change them, or remove them. If you have even more time on your hands you can replace the actual footstep sounds with your own recordings if you want, but I won't go into that in this tutorial.
There have been a few questions in the forums about changing this and other Half-Life files. It clearly says on most files not to change or modify them, this is mainly to ensure integrity of the original files.
Make sure you Back-up or Copy your original materials.txt before you modify it. If you want people to use your modified materials text, then upload your map as a minimod and include your new file in the Mods sound file. The server will automatically look in the mod's sound file first, and use any stuff you put in there. If there isn't a sound folder, then it will default to the valvesound folder.
Get into the habit of creating minimod folders for all the maps you are adding enhancements too. People don't mind running custom games, but DO mind overwriting original files.