The STFT is a mapping from a one-dimensional function (the domain, which is a function of time) to a two-dimensional function (the range, which is a function of time and frequency). Now suppose, rather than holding constant (4), we also allow it to be a parameter. The new mapping we so obtain is a mapping from the one-dimensional domain (time) to a three-dimensional range (time, frequency, and log-scale) that we previously referred to as the TFS parameter space (Fig. 1(a)).