## 4 Discussion
### Serial Measurements of DPOAEs \(\leq\)8 kHz
This difference in the amount of points available at baseline for continued monitoring is a practical and critical point for the consideration of having an objective, stable DPOAE measurement over time for the purpose of monitoring the pattern of progression of basal cochlear dysfunction (or preservation of cochlear function) throughout treatment. When DPOAEs are recorded using more closely spaced stimulus frequencies, as in the case of the concentrated sweep for the research approach at \(\sim\)1/8 th octave steps, a more detailed pattern of minima and maxima of DPOAE levels are revealed. As illustrated in Figure 5, we see that the more concentrated paradigm permits greater characterization of cochlear function as well as more data points to monitor  
Figure 5: Case illustration of an adult undergoing cisplatin therapy with serial measurement of DPOAEs over 3 trials, averaging 3 weeks apart displayed. DPOAE levels across f\({}_{2}\) frequencies (up to 8 kHz) using standard stimulus parameters (1.22; 65/55 dB SPL) tested using a clinical approach (**left panel**; SPL calibration; \(\sim\)4 points per octave) and research approach (**right panel**; FPL calibration; \(\sim\)8 points per octave). The solid lines with black triangles represent trial 1 (baseline) prior to exposures and the long-dashed lines with red squares or gray diamonds represent trials 2 and 3 (monitoring visits), respectively. The short-dashed lines without symbols are the average noise floor for all trials for the respective approach. The line at \(-\)20 dB SPL plotted as a reference for visual comparison. from baseline in the standard frequency range. This reflects a paradigm that can be readily employed on standard clinical equipment used in practices today. Moreover, considerable attention in terms of potential clinical utility has been given to even finer frequency resolution measurements, known as fine structure which is understood to be an interference pattern between multiple components of the DPOAE at 2f\({}_{1}\)-f\({}_{2}\) (e.g., [40; 41; 42]). DPOAE fine structure characterization has demonstrated little clinical utility in a population of 10- to 65-year-olds [21]. This highlights that there is an optimal configuration, likely defined by the suspected damage pattern, for what stimulus parameters hold the most clinical utility. When present, DPOAE levels were larger for the research approach in alignment with improved hardware, calibration and signal delivery capabilities highlighted in previous work [21; 39]. Most striking is the comparison between the two approaches for the average noise floors. These are distinctly different with a notably lower noise floor (\(-20\) to \(-30\) dB) for the research approach compared to the clinical approach (\(-10\) to \(-20\)). It should be noted that the average noise floor was higher at the lower frequencies for both calibration methods and approaches. This lower noise floor in the research approach permits the opportunity to expand SNR criterion for monitoring purposes. Furthermore, the ability to measure DPOAEs at baseline with the research approach permits an illustration (Figure 5) of the value of quantifying stable cochlear health in a region. Specifically, stable DPOAE levels are demonstrated 0.8-1.8 kHz for the research approach relative to baseline.