Hearing Pitch Breaks
A pitch break occurs when vocal cord swellings touch in the midline:
- As pitch increases, the cricothyroid muscles pull the vocal cords longer, limiting the maximum excursion of the vocal cords during each oscillation and forcing swellings to ultimately remain in contact with the opposite side throughout the entire vibratory cycle.
- As pitch increases, the cricothyroid muscles pull the vocal cords tighter, not allowing marginal swellings to press into the vocal cord body easily (conversly, at low pitch and tension, even firm swellings like nodules can be compressed into the body of the vocal cord during the closing impact).
- The sudden division of the vocal cord vibrating length by half causes the frequency of vibration to approximately double (although pitch depends on the length, tension and mass of the vibrating segment).
- The sudden division of the vocal cord vibrating length into anterior and posterior segments creates two sound sources.
Case study
History
Antonia began to notice a voice problem 10 days ago. She is a voice teacher in her mid-30s, with 20 years of vocal training herself as a mezzosoprano. Her upper notes began to cut out and then she lost some of her high notes completely. Now it is also affecting the quality of her speaking voice. The last time she lost her voice was 10 years ago. She is moderately talkative and rates herself a 4 on a 7-point talkativeness scale, although with children she has been using her voice more recently.
Vocal Capabilities
Her voice is melodic, but mildly rough on a reading task. Her maximum phonation time at her comfortable pitch is 13 seconds during which there is audible air leak. She has a full, 2.5-octave vocal range from C3 to G5. As she goes up in pitch, she sings loudly. At D5, her voice suddenly breaks upward in pitch almost an octave to B5. For vocal tasks at a soft volume I have her sing “Happy Birthday to you” at several pitches. She leaks air throughout the C4 to A4 range and cannot sing softly above A4. If she increase her volume, the pitch break occurs again.
Her voice is somewhere between clear and rough at a typical female speaking pitch so I layered the colors red and green. You could say it has a bit of a gravelly quality. The pitch break occurs in the upper right of the chart. She cannot get above A4 in the lower right at high pitch and low volume.
Laryngoscopy
To visualize the finding on endoscopy, the patient phonate at a pitch just below the problem are and then glide upward in pitch.
As she increases to pitch G4 the membranous vocal cords, separate during each oscillation. Here they're shown during the most open phase of the vibratory cycle.
As she attempts to increase to pitch G4#, her pitch suddenly jumps upward one octave and the membranous vocal cords, are split into two separate segments. The anterior and posterior segments are approximately the same length and vibrate on the same note. Here the vocal cords are shown during the most open phase of the vibratory cycle. The central swellings remain compressed throughout the vibratory cycle.
Summary
We can diagram pitch breaks on a pitch vs. volume plot. At some tightness, her pitch suddenly breaks and jumps upward. This occurs because the vibrating segments are suddenly half the length of the previous note after vocal swellings touch.
We can correlate this with a visual finding of the entire vocal cord vibrating as pitch is increased until the point where the membranous vocal cord is split into two segments.
Pitch breaks typically occur at higher volumes when a swelling firmly touches the other side and splits the membranous vocal cord’s vibrating length abruptly into two separate segments.
The mechanical phenomenon underlying a pitch break is nearly identical to an onset dealy from a swelling. The individual glides upward in pitch, but in this case utilizes a high subglottic pressure. The high subglottic pressure keeps the vocal cords vibrating even when the swellings touch. When the cricothyroid muscles pull the vocal cords taught to the point where the vocal cord swelling(s) are compressed against one another, rather than the vibrations stopping, suddenly the vibrating segment of the membranous vocal cords has been split nearly in half. A vibrating structure with half the length tends to vibrate at much higher rate, perhaps up to double and this leads to a large jump in pitch, perhaps as much as an octave.
It may be difficult to produce any sound at all in this in-between range.
The mid-cord swelling splits the vocal cords into two, equal vibratory segments. They may be out of phase, but since they are the same pitch, the strobe light tracks them both simultaneously.
We can diagram onset delays and pitch breaks on a pitch vs. volume plot. We can correlate this with a visual finding of something touching the vibrating vocal cord and dampening the vibrations at a specific pitch during stroboscopy.