Question

Passage:
In the late nineteenth century, linguistic geography and dialectology relied almost entirely on impressionistic field transcription, wherein trained fieldworkers recorded regional speech variations using specialized phonetic alphabets. This methodology came under fierce scrutiny following the emergence of experimental phonetics, pioneered by the French linguist Abbé Pierre-Jean Rousselot. Rousselot argued that human auditory perception was inherently subjective, prone to acoustic illusions, and incapable of capturing the minute physiological mechanics of articulation. To establish linguistics as an exact physical science, Rousselot adapted the kymograph—a rotating cylinder wrapped in smoked paper, originally devised for physiological research—to capture mechanical tracings of airflow, pitch, and vocal tract movements.

Rousselot’s mechanical apparatus utilized flexible rubber membranes (Marey tambours) and air-filled capsules connected via semi-rigid tubes to exploratory bulbs and artificial palates placed on a speaker’s lips, larynx, or inside the oral cavity. As the speaker articulated words, localized air pressure fluctuations deformed the membranes, causing lightweight recording styluses tipped with straw or metal to etch continuous wave patterns onto the soot-coated kymograph drum. By calibrating the drum’s rotational velocity against a vibrating tuning fork of known frequency, researchers could quantify the exact duration of phonemes, the onset of vocal fold vibration, and nasal air emission with millisecond precision. For the first time, phonetic phenomena that eluded human ears—such as micro-pauses before stop consonants and imperceptible vowel nasalization—were rendered visually measurable.

Despite its groundbreaking accuracy, Rousselot’s technique faced significant operational and theoretical resistance. Traditional dialectologists, notably Jules Gilliéron, creator of the Atlas Linguistique de la France, contended that laboratory apparatuses imposed unnatural physical constraints on informants, thereby distorting natural conversational cadence. Moreover, the physical inertia of the mechanical styluses and the pneumatic dampening inherent in rubber tubing imposed severe physical limits: the apparatus failed to register the rapid, high-frequency acoustic transients characteristic of fricatives like [s] and [ʃ], dampening amplitudes above a few hundred hertz. While Rousselot acknowledged that the apparatus could not resolve high-frequency acoustic energy, he maintained that its primary value lay in charting articulatory mechanics rather than acoustic waveforms. Nevertheless, this acoustic blind spot meant that while the kymograph excelled at documenting muscular timing and intraoral pressure, it could not provide a complete physical representation of the speech sound itself, necessitating the later development of electromagnetic and oscillographic recording methods.

Based on the passage, which of the following is an explicit limitation of Rousselot’s kymographic apparatus?