Ingo’s Register Treadmill

Abstract

Ingo's Register Treadmill Ingo Titze (bio) VOICE RESEARCH AND TECHNOLOGY A register treadmill was proposed eight years ago as a diagnostic exercise for exposing involuntary register shifts in the D4 to A4 pitch range.1 The basic concept was to create pitch and vowel progressions that would elicit maximum crossings of harmonics with supraglottal resonances (formants) of the vocal tract. It is well known that sudden increases or decreases in harmonic amplitudes in proximity of a resonance can cause a timbral change that can be considered an acoustic registration.2 In particular, strengthening or weakening the second harmonic with the first formant can be responsible for such a register shift. A pentavowel sequence, combined with a pentatonic scale, was proposed such that source frequencies move in opposite direction to resonance frequencies. This produces multiple harmonic-resonance crossovers. This article is a follow-up to expand the treadmill to include a wider pitch range and sex differences in formant frequencies. While allophonic variations of formants F1 and F2 are large across individuals and languages, a smoothed penta-vowel sequence has been chosen here. Each sequence begins with a wide mouth shape and ends with a narrow mouth shape. Formant frequencies for females have been chosen to be 20 % higher than for males. All formant frequencies are listed below for two vowel sequences. High Vowel Sequence [æ] [ɛ] [e] [ɪ] [i] Male F1 670 550 420 350 280 Female F1 860 660 504 420 320 Male F2 1800 1900 2000 2200 2300 Female F2 2160 2280 2400 2640 2760 Low Vowel Sequence [a] [Ɔ] [o] [Ʊ] [u] Male F1 850 500 360 300 300 Female F1 1020 600 431 360 370 Male F2 1610 800 640 610 595 Female F2 1932 960 768 732 714 In the treadmill, F1 is descending while fo is ascending to produce a maximum number of harmonic/formant crossings. Figure 1 shows the graphic display for a D4–A4 up and down pentatonic scale (solid lines), combined with the low vowel formant frequencies (dashed lines). Note that there are [End Page 197] Click for larger view View full resolution Figure 1. Treadmill for the D4–A4 pentatonic scale produced on low vowels; (a) male sequence and (b) female sequence. five crossings on the ascending scale for both males and females. For males, the crossings are: fo crosses F1 near the [o] vowel; 2fo crosses F1 near the [Ɔ] vowel 2fo crosses F2 near the [o] vowel 3fo crosses F2 near the [Ɔ] vowel 4fo crosses F2 near the [Ɔ] vowel. Note the importance of the [Ɔ] and [o] vowels in males in this region of the pitch range. For females, the same five crossings occur, but on slightly more closed-mouth vowels due to higher overall formant frequencies. For example, fo crosses F1 closer to the [Ʊ] vowel than the [o] vowel. Figure 2 shows the treadmill for the high vowel sequence. The pentatonic scale is kept the same, D4–A4. There are now only two major crossings: fo crosses F1 between [e] and [I] in males and between [I] and [i] in females; 2fo crosses F2 between [æ] and [ɛ] in males and between [ɛ] and [e] in females None of the first 4 harmonics cross the second formant F2. Thus, in this region of the pitch range (D4–A4), acoustic registration in high vowels is carried primarily by the first two harmonics. The fifth and higher harmonics are not plotted. They will interact with F2 and higher formants, particularly if fo is raised. Figures 3 and 4 show the treadmills when the pentatonic scale is raised to the G4–D5 range. Usually one progresses in half-steps to this higher level. Most of the high pitch range for males and female belters is then covered. Figure 3 shows the low vowel sequence. The bright [a] vowel is now included in the crossings, but the general picture has not changed much from the A4–D4 scale. Of special...