This is warm up going from a lower tone of chest voice to higher head tones. You will feel the resonating chambers move from your range in your throat, then your mouth and then your nose then all the way up to higher pitches in your forehead. This wakes up the stuffiness in the nose and loosens it by practicing this siren like effect on an m sound.
Practice speaking on a higher intonation. Say, Hi, how are you today? Then try in on a single M nasal consonant. Practice it through several times. Let’s begin an M on changing pitches. Go up the scale one note at a time. First on the low chest range and then add one note higher. This is great for learning to support the sound by forcing a little bit out and down with your abdomen. Keep one hand over the diaphragm two fingers above the belly button. And watch that the breath is exhaling and the stomach is hard and pushing out as you pitch up in range.
This change in pitch is a wonderful way to practice changing intonation while speaking with an American accent which tends to use a higher range of pitches (notes). This helps avoid monotone speech.
