In the modal register, the length, tension, and mass of the
vocal folds are in a state of flux which causes the frequency of vibration of the vocal folds to vary. As the tension of the vocal folds is increased, causing them to lengthen and their edges to become thinner, the
pitch of the resultant vocalisation rises. If any of the three factors were to be held constant, interfering with the progressive state of change, the
laryngeal function of the voice would become static and, eventually, breaks would occur, resulting in obvious changes in
vocal quality. While some vocal pedagogists identify such breaks as register boundaries or transition areas between registers, other vocal pedagogists maintain that the breaks are a result of vocal problems caused by a static laryngeal adjustment that does not permit the necessary changes to take place within the modal register. On the lower pitches in the modal register, the
vocal folds are thick and wedge-shaped. Because of the thickness, large portions of the opposing surfaces of the vocal folds are brought into contact, and the
glottis remains closed for a considerable time in each cycle. The glottis opens from the bottom before it opens at the top, which imparts a fluid, wavelike motion to the cords. The modal voice has a broad harmonic spectrum, rich in
overtones, because of the rolling motion of the cords. It is comparatively loud to the other vocal registers because of the vibratory energy present, but it is capable of dynamic variation.{{cite journal For the lowest tones, only the
thyroarytenoid muscles are active, but as the pitch rises, the
cricothyroids enter the action, which begins to lengthen the folds. As longitudinal tension increases, the glottis tends to develop a gap in the middle. To counteract the tendency, the lateral cricoarytenoids are brought into action, pulling forward on the muscular process of the
arytenoids. The process is sometimes referred to as medial compression.{{cite book In addition to the stretching of the vocal folds and the increased tension as the pitch rises, the opposing surfaces of the folds, which may be brought into contact, become smaller and smaller, as the edges of the folds become thinner. The basic vibratory or
phonatory pattern remains the same, with the whole vocal fold active, but the vertical excursions are not as large and the rolling motion is not as apparent as on the lower pitches of the modal register.{{cite book |title= The Voice and its Disorders |author1=
Greene, Margaret |author2=Lesley Mathieson |year= 2001 |publisher= John Wiley & Sons|edition=6E The physical limits of muscular strength of the internal thyroarytenoids or
vocalis muscle are being approached. To sing or speak above this pitch level, the voice must adopt a new phonatory pattern to change registers. == See also ==