The Last Levers: Soft Palate and Pharynx
So far you have learned almost all of the little levers you can use to change the sound of your voice. But there are one or two more at the back of the throat. You want to learn to move your soft palate and your pharynx to shrink the space in your throat, just like you have used your tongue and lips to shrink the space in your mouth. The effect is subtle, but it can often make the difference between an authentically feminine voice and one that just sounds... off, somehow.
You can see a very brief overview of the technique in this video. But to make it easier, start with just the soft palate. Look in a mirror and say "ahh" and then "ung" and watch how the back of your tongue comes up while the very back of the roof of your mouth (the soft palate) comes down slightly to meet it. When they touch, the air is blocked off from your mouth and forced through your nose instead, creating a hypernasal sound.
Try the exercises in this video to learn to control your soft palate, and by extension, your nasal resonance. Generally, you want to reduce this nasality for a more feminine sound.
Pharyngeal Constriction: Gargling and Beyond
The next thing you want to learn is how to constrict your pharynx, or close your pharyngeal wall. Doing this will bring in the sides of your throat just below the soft palate (oropharynx), pushing your tonsils against the back of your tongue.
How do you do it? Gargling. Say "ahh" while you tilt your head back and gargle, then tilt your head upright again and try to keep the sound going. Or say "ahh" from the top of a swallow-and-hold, or even a whisper siren. Eventually, you want to be able to say "ung" while sticking your tongue way out - the only way you can do that is to push in the walls of your oropharynx, because your soft palate cannot reach the back of your tongue while it is stretched out of your mouth.
If you talk at the same time, you will sound like Meatwad, as in this video.
Character Voices: Elmo, Smeagol, and the Loli Voice
If you start with a Meatwad voice and bring your pitch up into a falsetto with a fair amount of nasal resonance, vocal twang, and a lot of open quotient, what do you get? You get an Elmo voice, as in this video. The reduced space in the back of the mouth and throat is what gives Elmo's voice its child-like quality.
If you take that Elmo voice and bring the pitch down while constricting your pharynx as much as possible, you get a Smeagol or Gollum voice, as in this video. For Smeagol, you want to constrict not only the oropharynx but also the hypopharynx, further down the throat, to create a dampened sound like a sob or an old man.
You do not have to take it that far, but if you add just a hint of oropharyngeal throat closure, you can make your voice sound younger and more feminine. This is most clearly demonstrated with a "loli" voice, as in this video. If you whisper with a feminine vocal posture and then squeeze in the back of your mouth and throat a little, you can sound like a cute anime girl. Try it!
Singing Application: The Britney Spears Sound
These are also important elements for singing feminization, especially for a voice like Britney Spears, which combines a fair amount of oropharyngeal constriction with a very hyponasal sound, as if from a stuffy nose. You can hear it exaggerated in this video. Imitating that sound is a great way to learn to achieve throat closure while simultaneously eliminating nasal resonance.
Practice and Safety
Your homework is to spend some time every day trying to talk like Meatwad and the other characters, by playing with your soft palate and pharynx position. Be sure to try whispering too, especially for the loli voice. Use the recording steps in your practice to capture and play back your character voices, to hear how they actually sound. Do not worry about whether they match a specific character exactly, just see what sort of funny voices you can make!
Then try adding a hint of throat closure to your speaking practice, to see if you can use it to sound more feminine. Record and play back your feminine voice experiments to help guide your practice.
If throat discomfort appears, stop and recover. Sustainable coordination is the goal, not maximal constriction.