We read the article by Kim et al. [1] with great interest. Since tinnitus is common among otological patients and serious if untreated, the comparative study on different sounds in relieving tinnitus is relevant. The information gathered from the study is useful to direct clinicians in providing an optimum stimulus for sound therapy in tinnitus sufferers.

The authors found the highest improvements in broadband noise tinnitus retraining therapy (bTRT) group, followed by mixed noise TRT (mTRT) group and narrowband noise TRT (nTRT) group. This finding is in line with the previous studies [2,3] indicating that bTRT is effective to treat tinnitus to some degree. In this regard, we would like to highlight some issues that might be worthy of consideration. For tinnitus management, we prescribe customized sound therapy (coupled with a specific counseling module) to eligible patients on a regular basis. From our clinical experience, we have been observing a consistent pattern where patients with more severe tinnitus tend to show higher improvements compared to those with milder form of tinnitus. Our observation, even though not scientifically proven, is in line with a study by Henry et al. [2]. In this study, patients with 'very big tinnitus problem' showed significantly greater improvements than those with 'moderate tinnitus problem' after undergoing TRT. Herein, it seems that the baseline tinnitus severity has influence on TRT outcomes. In the study by Kim et al. [1], it is noted that on average, bTRT group had more severe tinnitus (Tinnitus Handicap Inventory [THI]=54.22±22.41) compared to mTRT (THI= 42.5±22.27) and nTRT (THI=48.25±25.56). In this matter, it seems possible that the superior performance of bTRT could also be contributed by the tinnitus severity factor. On the other hand, mTRT procedure is relatively new and its 'true' potential in treating tinnitus has not been revealed in large-scale studies. The mTRT employs a sequential technique (where different types of noise were given at specific time intervals) and offers a novel way for tinnitus treatment. The sequential technique for sound therapy has been found to be effective in treating tinnitus [4].

If a similar study to be expanded in future, perhaps the tinnitus treatment groups to be compared should have almost equal baseline tinnitus severity scores. If this is unachievable, applying analysis of covariance can be useful. By using the baseline tinnitus severity as the covariate (e.g., THI score), comparing the outcomes among different sound therapy groups would be more valid as the tinnitus severity is controlled.