Jitter analysis of an MMPP-2 tagged stream in the presence of an MMPP-2 background stream

We first consider a single-server queue that serves a tagged MMPP-2 stream and a background MMPP-2 stream in a FIFO manner. The service time is exponentially distributed. For this queueing system, we obtain the CDF of the tagged inter-departure time, from which we can calculate the jitter, defined as a percentile of the inter-departure time. The formulation is exact, but the solution is obtained numerically, which introduces an error that has been found to be negligible. Subsequently, we consider a tandem queueing network consisting of N tandem queues, which is traversed by the MMPP-2 tagged stream, and where each queue also serves a local MMPP-2 background stream. For this queueing network, we obtain an upper bound on the CDF of the inter-departure time from the Nth queue using a heavy traffic approximation, and we verify it by simulation.     

A Comparison of Trained and Untrained Vocalists on the Dysphonia Severity Index

The purposes of this study were (1) to compare trained and untrained singers on the Dysphonia Severity Index (DSI) and its component measures, and (2) to contribute to normative DSI data for trained singers. This study included 36 untrained participants (15 males and 21 females) and 30 participants (15 males and 15 females) with singing experience between the ages of 18 and 30 years. Measures of maximum phonation time (MPT), highest phonational frequency, lowest intensity, and jitter were obtained for each subject and incorporated into the previously published multivariate DSI formula. Results indicated that vocally trained subjects have significantly higher DSI scores than untrained subjects (mean DSI: 6.48 vs 4.00, respectively), with significant differences observed between trained and untrained groups for three of the four components of the DSI (F₀ high; I low; jitter). The findings of this study are consistent with previous reports that indicate significant increases in the DSI with vocal training, and with various studies that have observed increased vocal capability in trained singers versus their untrained counterparts. The results of this study indicate that alternative normative expectations for the DSI may need to be taken into account when using the DSI with patients who have participated in directed vocal training, such as choral participation and voice/singing lessons.