“…Existing NLE techniques can be categorized into two main classes. The first one is the heuristic or expert driven approaches, e.g., [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24]. These consider various approaches regarding, e.g., formants, transients, Lombard speech, spectral shaping and dynamic range compression, or plain audibility.…”