A perceptual loudness function which outputs loudness in sones; this is a variant of an MP3 perceptual model, summing excitation in ERB bands. It models simple spectral and temporal masking, with equal loudness contour correction in ERB bands to obtain phons (relative dB), then a phon to sone transform. The final output is typically in the range of 0 to 64 sones, though higher values can occur with specific synthesised stimuli.
[fft] Audio input to track, which has been pre-analysed by the FFT UGen; see examples below for the expected FFT size.
[sk] Spectral masking param: lower bins mask higher bin power within ERB bands, with a power falloff (leaky integration multiplier) of smask per bin.
[sk] Temporal masking param: the phon level let through in an ERB band is the maximum of the new measurement, and the previous minus tmask phons.