Effects of Historical Recording Technology on Vibrato in Modern-Day Opera Singers.

Objective: Past literature indicates that vibrato measurements of singers objectively changed (i.e., vibrato rate decreased and vibrato extent increased) from 1900 to the present day; however, historical audio recording technology may distort acoustic measurements of the voice output signal, including vibrato. As such, the listener's perception of historical singing may be influenced by the limitations of historical technology. This study attempts to show how the wax cylinder phonograph system-the oldest form of mass-produced audio recording technology-alters the recorded voice output signal of modern-day singers and, thus, provides an objective lens through which to study the effect(s) of historical audio recording technology on vibrato measurements.

Methods: Twenty professional Western opera singers sang a messa di voce on the vowel [a] and on the pitch C for male singers and C for female singers, three times into a flat-response omnidirectional microphone and onto an Edison Home Phonograph simultaneously. The middle 1-3 seconds (6-10 vibrato cycles) of each sample was analyzed for vibrato rate, vibrato extent, jitter (ddp), shimmer (dda), and fundamental frequency for each recording condition (wax cylinder phonograph or microphone). Steady-state and frequency-modulating sinewave test signals were also recorded under the multiple recording conditions.

Results: Results indicated no significant effect of recording condition on vibrato rate (mean [standard deviation], cylinder: 5.3 Hz [0.5], microphone: 5.3 Hz [0.5]) and no significant difference was found for mean fundamental frequency (cylinder: 389 Hz [137], microphone: 390 Hz [137]). A significant main effect of recording condition was found for vibrato extent (cylinder: ±103 cents [30], microphone: ±100 cents [31]). Additionally, mean jitter (ddp) (cylinder: 1.22% [1.09], microphone: 0.24% [0.12]) and mean shimmer (dda) (cylinder: 9.40% [4.90], microphone: 1.92% [0.94]) were significantly higher for the cylinder recording condition, indicating more cycle-to-cycle variability in the wax cylinder recorded signal. Analysis of test signals revealed similar patterns based on recording condition.

Discussion: This study validates past scholarly inquiry about vibrato measurements as extracted from digitized wax cylinder phonograph recordings by demonstrating that measured vibrato rate remains constant during both recording conditions. In other words, vibrato rate as measured from historical recordings can be viewed as an accurate representation of the historical singer being studied. Furthermore, it suggests that the value of prior vibrato extent measurements from these acoustic recordings may be slightly overestimated from the original voice output signals produced by singers near the beginning of the 20th century (i.e., a narrow vibrato extent might have been numerically smaller on average). Increased jitter and shimmer in the wax cylinder recording conditions may be indicative of nonlinearities in the phonograph recording or playback systems.