The thyroid arytenoid (TA) is the muscle that is primarily responsible for chest voice sound color. Thus, for purposes of simplification we could say that chest voice is a TA dominant phonation. This applies to speech mode so when you speak, you could say you’re sound color comes from a very TA dominant phonation. In contrast, the Cricothyroid musculature (CA) is primarily responsible for the change in pitch. Thus, when you belt, you want to engage the CA for the increase in pitch while using the TA muscle to maintain the dark sound color of chest voice when singing high.
In the video, Robert Lunte explains how the engagement or disengagement of the TA muscle affects the sound color in your singing. If your TA musculature releases when you sing high (something that most of us intuitively do), your sound color will be falsetto-ish and you’ll get that break in the middle. In the video, Robert demonstrates with an animation what happens when the TA musculature disengages as we sing higher.
The reason we place such an emphasis on mastering a smooth transition through the vocal break is because maintaining the TA musculature engaged is not intuitive. In order to be able to sing strong high notes, we need to overcome the initial urge to release the TA muscle above the vocal break. Once we accomplish this, we are able to sing high notes with a “chesty sound color”, this technique is generally referred to as belting.
Although initially the body might not want to go into a TA dominant position above the vocal break, with training and technique any singer can achieve a TA dominant sound color for their high notes. What you need to understand is that the TA and CT musculatures do not work like biceps and triceps. You do not have to choose one or the other. In fact, if you want to sound chesty when singing high, you should think of them like members of the same team. Think about activating them simultaneously when singing into the head voice through the vocal break.
Training the TA muscle to remain engaged through the vocal break is a significant portion of a contemporary singer’s training. In The Four Pillars of Singing, we train this by using the resistance training vowel modification formulas as well as the resistance training onsets. More specifically, we recommend you pay special attention to the Attack and Release, Dampen and Release, and Contract and Release onsets for building your belting voice.