This is the autocorrelation of the polynomial, not a signal autocorrelation. The NumOfBands perceptual filters are spaced evenly on a bark scale covering the Nyquist interval of the signal. The magnitude of the FT is converted to equivalent loudness before filtering, and filter outputs are the natural logarithm of the weighted sum of the linear amplitude equivalent loudness values. The energy level in each channel is stored in Bands. The input parameter sr must contain the waveform sampling rate in samples per sec.
Failure is always due to inability to allocate memory needed for tables during the analysis.
Linear interpolation is used to estimate loudness at frequencies between those in the table. The returned spectrum is NPT points evenly spaced on a Bark scale and smoothed to BRES resolution. Mariusz Fecko did some cleanup work on the zcep function.