and Harsh vocals will grow in volume as you gain skill with them. To answer ur question posted on CC's video Death Walking Terror

that's how I learned at least.

Try going sssssss quietly and then increase in volume. The feeling in your stomach is your diaphragm. This is what you want to feel when performing death metal vocals.

Pick a lyric you want to perform. Always try to pick songs from bands like Slayer, Metallica or other bands who do not use the death grunts as it will be easier to rehearse your grunts. Try singing it normally, then slowly add more "fire" to it, until you can feel your diaphragm really pushing and you're getting that deep sound you're looking for. If you don't succeed in the deep guttural vocals try the raspier approach to these vocals like Mark Hunter of Chimaira. Anyone can achieve this, men as well as women (listen to the current vocalist for Arch Enemy). So long as your vocal range is Alto or lower. Arch Enemy's Vocalist Angela Gossow is an alto, and will say herself, if you are a Soprano, don't even try Death Growls.

If u don't already do this, than this will help with ur voice.

Listen to any album using harsh vocal techniques. If you're not already familiar with the genre, browse the links listed below. Buy CDs from bands and singers whose voices you admire.
Learn how to sing properly. The most important technique for performing death metal vocals is to be able to control your breathing, establishing a balance between the force used by your diaphragm and your vocal cords. Using only the vocal cords will put undue pressure on them and is sure to damage them (minor damage will heal in time). Proper technique is established by using the diaphragm to push air out of your lungs.