The hum in the last lesson has a family. Lip trills, tongue trills, and singing through a narrow straw all work on the same principle, and voice clinics and teaching studios use them constantly. The name is a mouthful, semi-occluded vocal tract exercises, so most people say SOVT.
The idea is that partly closing the mouth creates a little back-pressure, and that back-pressure lets the vocal folds vibrate with less effort. The practical result is that you can take your voice across its whole range, including the parts that usually crack or strain, with far less strain. That is why this lesson comes before any work on pitch or registers. It gives you a safe way to visit the whole instrument first.
What to notice
The exercise is a lip trill on a long arc, up an octave and a half and back down. The piano doubles the melody the whole way, and you will need it, because the buzz gives you less to go on than an open vowel. There is no scoring on the trill; the app cannot read pitch through it. Follow the piano and keep the buzz going.
The thing to watch is whether the trill stops. It usually stops for one of two reasons. Either you have run low on air, or you have tensed somewhere, often the jaw or the corners of the mouth, as the line climbs toward the top. If it stops, restart it on the next note rather than forcing it. A trill that keeps going through the top of the arc is the whole goal.
Some people cannot lip trill at all at first. Press two fingertips lightly against your cheeks near the corners of your mouth, which takes some of the weight off the lips, or switch to a tongue trill or a hum on the same pattern. The guide covers the alternatives.
What done means
You are done when you have followed the piano through the full arc, in a few keys, without the trill collapsing on the way up. Do not worry about the highest keys on day one.
Add this to your routine if the trill works for you. Between the hum and the trill you now have a two-exercise warm-up, and the next lesson is the first one where the app starts scoring you.
The exercise
Rossini Lip Trill
Follow-along, not scored
About this exercise
Builds a full-range SOVT warm-up through the entire passaggio with reduced vocal-fold collision (the lip occlusion raises pressure in the mouth and lowers the pressure drop across the folds). The octave-and-a-half arc forces smooth register bridging and the piano doubles the melody as a pitch reference, since the buzz gives less to go on than an open vowel and the app cannot score a trill.