Returns a list with the frequency (Hz) and depth of amplitude
modulation (dB relative to global max, normally at 0 Hz).
Arguments
m
numeric matrix of non-negative values with colnames giving temporal
modulation frequency
amRange
the range of temporal modulation frequencies that we are
interested in as "amplitude modulation" (AM), Hz
amRes
controls the width of window over which we look for local maxima
Details
Helper function for calculating amplitude modulation based on the modulation
spectrum. Algorithm: averages AM across all FM bins in the positive half of
the modulation spectrum and looks for a peak in the specified AM frequency
range.