Ok, so in western music, most singing can be thought of as a deviation in some way from the singing techniques in play from approx 1670-1840 (this is kind of an insulting view for a dozen reasons but that’s beyond the scope of this post).

This singing is based on consistent support of breathing from core muscle support, which creates a consistent flow of air across the vocal chords. How this is done exactly differs between the national “schools” (variations in style) but mostly its engaging the lower abdominal muscles to create a “platform” for the diaphragm to rest on, This results in no variations in pitch or intensity across a note or phrase. Some 19th century Italian teachers are reported to have focused solely on breathing and posture for 6 months before the student was allowed to sing a note. (probably untrue, but they do focus most on the breath.)

As an excercise, stand in second position (“at ease” if you don’t know ballet positions) take a deep breath, and try to not let your chest fall downwards as you run out of air on a note. That’s kind of what we’re talking about.

The other part is placement. where in the head the column of air is focused in your internal sensations. Different genres of music have very, very, different ideas on optimal placement, as do the different classical schools, but for this, try lifting your soft palate (the upper jaw behind your tounge) on a note, and feel where the vibration is in your skull on an ah or eh vowel.

Most classical schools want the palate high, the larynx (the voice box) low, creating sort of a near yawn sensation, and the resonance forward, between and slightly above the eyes, in “The mask”. Most “popular” (again, for another rant) styles want a higher larynx to help diction, though a high palate is often useful and with other techniques like “Cover” (modifying a vowel to make it easier or more beautiful sounding) you can use a classical technique and produce, to a point, a popular sound.

Vaccai was a composer, singer, and teacher of the late early romantic period (Think Barber of Seville and the “Figaro” song) and was a conservative methodologically at a time when a more robust mode of vocal production (more like what we think of as the operatic sound) was becoming popular.

He wrote a book. designed for amateurs who wanted to sing at a high level. It’s short and the excercises are short art songs based on traditional Italian poems. It’s also very comprehensive and many professionals use the excercises daily. It has terrorised beginner singers for 180 years. I strongly recommend you try the first excercise, and try to sing the phrases on one breath, focusing on getting the vowels unchanging. If you don’t have a keyboard. there are plenty of examples on you tube to sing to.

This isn’t an attempt to get you to be classical in method or that classical is the only or best method of training. but what it does right are some really nice skills to pick up, especially if you have pitching issues.

Finally, I might note, the modern 12 tone equal temperament scale is very slightly out of tune by design, for complex musical reasons. Natural singers with good pitch tend to differ a little without an accompanying instrument.