The only way your 'tone' can be improved/changed is through a technique called 'placement.' We have the ability to speak or sing from 4 different resonating areas in the body. These resonating areas are important to use because sound is produced in one or more of these places. We can make our speaking and singing richer, darker, lighter, less nasal, more powerful and even add clarity. Try this exercise to project your present sound. Don't worry about your sound being a bit nasal. It will vanish as you learn how to open the back of the throat.
1. Phonate, using the "ing" found in the word 'sing.' Hold on (sustain) the ing, and feel the buzzing sound resonating in the nose area and throughout the sinus cavities (the nasopharyngeal or mask area.) Repeat this exercise several times concentrating on the 'tingling' feeling. You are now making sound using the 'mask area.'
2. This time speak or sing words ending in "ing" such as thing, sing, ring, bing, ding, ming, king, wing.
This is an example of just 1 of the resonating places that will change your vocal sound. There are more.
I've written hubs about the voice. I think they will help you. Also recording your present speaking sound as you try to lower the pitch (or raise it) can be helpful.
I wish you every success and try not to be too critical of your sound as you learn correct exercises that will give you the speaking tone you like. The sound is inside you and waiting to emerge. It's already there. Proper tutorials either by an expert or following the right exercises you are given will release the sound you want.
