Effects of different calibration schedules on the test-retest differences of nasalance scores obtained with the Nasometer 6450.

ABSTRACT

Nasometry is used to assess nasality in speech but it is unclear whether overly frequent recalibration of the instrument adds measurement errors. The goal of the present research study was to describe the effect of the Nasometer 6450 calibration on the nasalance scores of repeated recordings. In a first experiment, the Nasometer calibration values stored in the computer's registry were manipulated to investigate the impact on nasalance scores. In the second experiment, a set of pre-recorded speech samples was re-recorded 40 times with a Nasometer 6450 in 4 different calibration regimens Short-term repeated recordings without (R1) and with recalibration (R2C), and long-term repeated recordings over 10 days without (R3) and with recalibration (R4C). The first experiment showed that, compared to a calibration value of 1.0, a value of 0.9 resulted in nasalance scores that were on average 3 points lower while a calibration value of 1.1 resulted in scores that were 0.5 points higher. The results of the second experiment showed test-retest differences of less than 2 nasalance points for 91% of the data for a non-nasal stimulus. For a nasal stimulus, 91% of data were within 5 points for R3 and R4C. The results suggested that frequent recalibration of the Nasometer may slightly increase test-retest differences of nasalance scores. An alternative procedure for verifying microphone balance without recalibration is suggested.