Internal soundgen function.
getVocalFry_per_epoch(rolloff, pitch_per_gc, nSubharm,
sideband_width_vector, throwaway01)matrix of original amplitudes of each harmonic in f0 stack
returned by getRolloff (columns=time, rows=frequency bins)
vector of the same length as ncol(rolloff)): f0 in Hz, one value per glottal cycle
the number of subharmonics to generate (a positive integer). If nSubharm==1, subFreq = f0 / 2. If nSubharm==2, subFreq = f0 / 3 and 2 * f0 / 3. Etc
(either numeric or vector of the same length as pitch_per_gc): regulates how quickly the strength of subharmonics fades as they move away from harmonics in f0 stack. Low values produce narrow sidebands, high values produce uniformly strong subharmonics
discard harmonics that are weaker than this number (between 0 and 1) to save computational resources
Returns a modified rolloff matrix with added subharmonics
Helper function for adding vocal fry (subharmonics) to a single epoch, with
unchanging subharmonics regime (fixed number of subharmonics and sideband
width). See master function getVocalFry.