In the attributes this is called: “
threshold for perceptual spectral *rolloff* in percent of spectrum”.
The name says something different: it is a stop band for the spectral deviation.
Also the unit does not seem to be a percentage of the spectrum.
The same goes for HarmonicSpectralDeviationStopBand.
See also pipo.catalog.
What does this actually do?
The Peeters paper (2004) does not really substitute for some real documentation.