New Evidence That Nonlinear Source-Filter Coupling Affects Harmonic Intensity and fo Stability During Instances of Harmonics Crossing Formants.
Lynn Maxfield, Anil Palaparthi, Ingo Titze
PMID 27501922WHAT IT FOUND
Voice intensity peaks became uneven and pitch jumps appeared when harmonics crossed vocal tract resonances in eight healthy adults using tube extensions.
The voice and vocal tract likely interacted in a nonlinear way.
Key findings
01Of 352 harmonic-formant crossings in 144 tokens, 266 (76%) showed asymmetric intensity slopes.
02Of 625 pitch-rate instabilities, 534 (85%) were associated with the first four harmonics crossing the first three formants, more than expected by chance.
03Intensity peaks for harmonics crossing formants did not align with formant centers, and the rising and falling sides of the peaks were not symmetrical.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
Only eight healthy adults were studied, so the findings do not show what happens in people with voice disorders. All recordings were made through tubes that lengthened the vocal tract, not through the natural vocal tract used in everyday speech. The tube task made formants lower and crossings more likely, so it is not representative of normal speech. Formant frequencies were estimated from vocal fry segments, and the authors could not confirm that formants did not shift during the glide. Total intensity drifted upward during glides and was corrected by analysis, which may affect interpretation of intensity peaks. The paper does not test any therapy or patient outcome.
The easy way to misread this
Do not read the 85% association as proof that a therapy works. The study used eight healthy adults with tube extensions and did not test treatment.