Cricothyroid approximation is a procedure designed to mimic the function of one set of your vocal muscles, the cricothyroid muscles. This pair of muscles is one of the groups of muscles that raises your pitch. Specifically they are the muscles that put your voice into falsetto. When they are relaxed your pitch is lower or in the chest register. The surgery typically truncates the lowest pitches. It does not change speech patterns, intensity, resonance or inflection characteristics of the male voice into a female pattern.
Your original voice in falsetto will sound the same after surgery as before surgery, so you can test out what your voice will sound like by speaking in falsetto. The surgery tries to prevent or limit dropping back down into the chest voice but doesn’t alter the quality of the falsetto voice. The surgery then doesn’t change the voice, it limits it. This can be a desirable limitation by relieving the effort of always trying to keep the voice up in falsetto. It also generally prevents an inadvertent drop into a deeper voice at an inopportune moment.
I have two main concerns with the surgery. Because the quality of the voice frequently has a falsetto quality, even when the pitche is higher the speaker may sound more like a gay male than a female. The second significant risk of this surgery is that about 1/3 of patients have their vocal cords stretch back out and their pitch drops back to their original pitch even though the surgical sutures remain tight. The individual has then lost the use of these muscles but still has a comfortable speaking pitch in the male vocal range. The individual may have lost their lowest pitches and that remains a benefit, but the speaking pitch remains unchanged. This frequently happens within a month or so of the procedure.
Consequently, I have stopped performing this surgery because of it's unpredictability. It is one of the easiest surgeries to perform, but I cannot predict who will be too squeaky and who will drop back down to their original pitch after surgery. In general, it is a very standardized surgery and perfomed similarly by different surgeons.
A smaller problem is that when you lose the use of your cricothyroid muscles, you also lose some of your ability to get loud since we use the cricothryoid muscles to support the vocal cords during loud sound production.
I have also had a patient who was locked into a single pitch and could neither move up nor down in pitch after the surgery.
You may listen to some pre- and post-surgical voices here. These are from surgeries are performed some years ago.