## 3 Results  
### Measurement of HF DPOAEs (up to 16 kHz)  
DPOAEs elicited with HF stimuli can be measured in newborns. Average DPOAE levels compared with the average noise floor from 2 through to 16 kHz across the two trials for each calibration method are shown in Figure 2 for newborns with present emissions. The left panel in Figure 2 displays the results obtained with FPL calibration and in the right panel are the results from traditional SPL calibration. In each panel, the solid and long-dashed lines represent trial 1 and 2, respectively, and error bars are standard error of the mean (SEM). The short-dashed lines denote the average noise floor across the two test trials for those who had present DPOAEs. It should be noted that, despite using research equipment, the average noise floor levels are higher (worse) at all frequencies than have been recorded when testing in a quiet room within a clinic [51] and in a room housed in an infusion center [53], but are no worse, and actually better, than the typical noise floor measured with clinical  
Figure 1: The red eartip (3–5 mm Flanged Sanibel Red Silicone) used initially in this study is shown on the left and the yellow eartip (3 mm Flanged Sanibel Yellow Silicone) used for the remainder of the study is shown on the right. equipment. For DPOAE levels to be considered present a signal-to-noise ratio (SNR) of 6 dB and a level greater than \(-\)20 dB SPL needed to be met, so not every data point includes data deemed present from all 26 ears at each of the seven frequencies tested. In addition, one newborn was too noisy to be tested with the final discrete frequency sweep using FPL calibration so there are only 25 newborns represented in trial 2 for FPL calibration. The number of newborns with present DPOAEs at each frequency for each trial are indicated just above the frequency on the \(x\)-axis. The top row of numbers is for trial 1 and the bottom row for trial 2. The frequency with the greatest number of ears with present DPOAEs is 8 kHz, no matter which calibration method is used. Generally, the least number of newborns with present DPOAEs occurred at the lowest (2 kHz) and highest (16 kHz) frequency tested for both calibration methods. When examining data from all frequencies tested (\(n\) = 357), for data obtained with FPL calibration, 56 (16%) data points did not meet the overall level criterion of \(>-\)20 dB SPL whereas 113 (32%) of the data did not meet the criterion of a 6 dB SNR. If we examine these same values for frequencies of 10 through 16 kHz (\(n\) = 203) and 2 through 8 kHz (\(n\) = 154), 50 (25%) and 6 (4%) did not meet the criterion of \(>-\)20 dB SPL and 55 (27%) and 58 (38%) did not meet the criterion of a 6 dB SNR, respectively. For SPL calibration, when examining data from all frequencies tested (\(n\) = 364), 78 (21%) data points did not meet the overall level criterion of \(>-\)20 dB SPL whereas 118 (32%) of the data did not meet the criterion of a 6 dB SNR. While examining these same values for frequencies of 10 through 16 kHz (\(n\) = 207) and 2 through 8 kHz (\(n\) = 157), 63 (31%) and 13 (8%) did not meet the criterion of \(>-\)20 dB SPL and 53 (26%) and 65 (41%) did not meet the criterion of a 6 dB SNR, respectively. This means that the majority of the data that did not meet the criteria of present at frequencies of 2 through 8 kHz were due to poor SNR, which is apparent with the high noise floors seen at these frequencies. Whereas, for frequencies of 10 through 16 kHz both poor SNR and decreased levels led to the classification of not present. For those with present DPOAEs, results are similar across the trials for both calibration methods. The overall DPOAE level is similar across the two calibration methods with the greatest levels occurring for frequencies of 8 kHz and below. The minimum, maximum, and average difference between DPOAE levels using FPL and SPL calibrations across both trials are 0.29 (16 kHz T1), 5.08 (12 kHz T2), and 2.16 dB, respectively.