[fig:melspecs]</a> b.3) was designed to remove magnitudes that fall below a defined threshold and to let the remaining magnitudes through. Thus, by constructing this filter with the gradients and applying it to the original sound, the regions of the gradients where energy is present will let the original sound pass to the following iteration. In other words, the original sound is convolved with the gradients, and the order of the inputs for the convolution can be easily flipped to construct the filter with 