This section involves a sub-octave generator that extracts a fundamental note form the audio in and drops it by one octave. Rather than simply mix this sub-octave with the original signal something more sophisticated is done. A ‘pseudo’ ring modulation effect occurs where instead of multiplying two waveforms, the RingMod just adds a half wave rectified version of the fundamental to the output of the Top Boost and thus can produce a fundamental that is double in frequency... so a bit like what happens with a standard RingMod where the frequency of a sine wave sent in is doubled though waveform multiplication.   But in the Hi-Fli RingMod version one doesn't hear the typical metallic/bell like sounds. Rather this pseudo RingMod signal is sent to a pair of FETs which act as modulators... modulated by the sub-octave signal. The result is some great deep sub-octaves, the amount of which are controlled by the RingMod and sub-octave levels.