Summarize:

If you want to change your voice to make it sound either higher or deeper, start by recording yourself so you'll know what approach to take. Use a recording device to capture the sound of your voice talking quietly, talking loudly, and singing. How would you describe the sound of your voice? What would you like to change? Does your voice sound nasally or gravelly? Is it easy or difficult to understand what you're saying? Is your voice breathy or clear? Many people have a voice that can be described as "nasally." A nasally voice tends to sound unnaturally higher than it should, because it doesn't have a chance to resonate properly to produce a deeper tone. This type of voice can sound grating to others as well as being difficult to understand. Make the following changes to eliminate that nasally sound: Make sure your breathing passages are clear. If you tend to have allergies or your nose is often clogged for other reasons, your voice is going to be stunted and nasally. Clear up your allergies, drink plenty of water and try to keep your sinuses clear. Practice opening your mouth wider when you speak. Drop your jaw and enunciate your words lower in your mouth, rather than producing them in your soft palate. In order to correct a high voice, many people speak from the back of their throat to produce a falsely deep tone. It's hard to get the proper amount of volume when you're straining to speak from the back of your throat, so doing this produces a muffled, difficult-to-interpret voice. In addition, speaking from the back of your throat in an attempt to sound as though your voice is deeper than it really is puts strain on your vocal cords and can cause a sore throat and voice loss over time. In order to make your voice sound deeper and more full, it's necessary to speak through your "mask," which is the area comprised of both your lips and nose. Using your entire mask to speak gives your voice the best chance of sounding a bit lower and richer. To determine whether you're speaking through your mask, touch your lips and nose as you speak. They should vibrate if you're utilizing the entire area. If they don't vibrate at first, experiment with different sounds until you find a way of speaking that works, then practice speaking that way all the time. Breathing deeply and projecting from your diaphragm is key to having a full, rich, strong voice. When you're breathing deeply, your stomach should move in and out with each breath, rather than your chest rising and falling. Practice projecting from your diaphragm by pulling your stomach in to exhale as you speak. You'll notice that your voice rings out loud and clear when you breathe this way. Doing breathing exercises in which you focus on deep breathing will help you remember to project from your diaphragm. Exhale, pushing all the air from your lungs. Once your air runs out, your lungs will automatically begin to inhale deeply in an attempt to satisfy your need for air. Pay close attention to how your lungs feel when you take a deep breath. Inhale comfortably and hold your breath for 15 seconds before exhaling. Gradually increase the amount of time you hold your breath to 20 seconds, 30 seconds, 45 seconds, and 1 minute. This exercise strengthens your diaphragm. Laugh heartily, purposefully making a "ha ha ha" sound. Expel all the air from your lungs with your laugh, then inhale deeply and quickly. Lie on your back and place a book or solid object on your diaphragm. Relax as much of your body as possible. Pay close attention to the movement of your diaphragm, noting how the book rises and falls as you breathe. Flatten your stomach as much as possible when you exhale, and repeat until you automatically expand and contract your waist with each breath. Inhale deeply while standing. Exhale, counting aloud from one to five with a single breath. Repeat the exercise until you are able to comfortably count from 1 to 10 on one exhale. When you get the hang of speaking this way, you should be able to project so that your voice can be heard by people on the other side of the room without causing you to become hoarse. The human voice is capable of producing sound in a range of pitches. Speak in a pitch higher or a pitch lower to temporarily change your voice. Pitch is altered in large part by the laryngeal cartilage. This is the movable piece of cartilage that rises and falls in your throat as you sing a scale: doh, re, mi, fa, sol, lah, ti, doh. Raising the laryngeal cartilage raises your pitch and creates a more feminine sound. Dropping the laryngeal cartilage drops your pitch and creates a more masculine sound.
Figure out what you sound like. Stop talking through your nose. Don't speak from the back of your throat. Speak through your "mask". Project from your diaphragm. Change your pitch.