I’ve been a vocal coach officially since 1994 but I worked with vocalists all the way back to 1975. Chest voice is called chest voice because someone at some time noticed that the chest vibrated, when he/she sang in the lower part of the range. The same is true for high notes and the vibration felt in the head. Some people call middle voice “mixed voice”.
First, I would point out that it is not necessarily an accurate description and can be misleading to think that you are mixing head voice and chest voice.
Secondly, middle voice is in the passaggio, which has been mis-translated as “passage area” when in fact, it means passage way.
Thirdly, many people are confused about the ranges of a voice and mistakenly believe that chest voice is a specific sound and that head voice is a specific sound and middle voice is a blend or mixture of the two. When your voice is working at its optimum, there is not a radical difference in your sound from one register to another. In fact, you should be able to do a glissando, seamlessly, from chest voice up to head voice and also in the opposite direction and at any volume level. If you cannot do that, something is not working correctly.
You should have the freedom of your entire range, without breaks or “shifting gears” and also with whatever quality you wish for expressing yourself artistically. One other thing to consider is that you should be able to sing as if you have one voice, not two or three. As a singer progresses in training with me, he or she may find that there will be variables with an overlap of ranges as far as how it feels to the singer.
It ALL blends after being properly trained and with no strain or hoarseness involved. We are working toward a consistent sound with effortless control, ultimately. Make sense? My site is