Sonnox Oxford Restore - Manual (Page 14)

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quickly wandering fundamental. This mode operates on MF and HF frequency selections only
(if Fast is selected in the LF range, the mode is forced to Auto and the Auto button flashes).
Auto and Fast modes are both applicable to Comb or Para-EQ settings. Fast mode is most
appropriate for quickly drifting high frequency buzzes possibly generated by lighting
interference.
4.3 Removal Filters
The default removal filter is a Comb filter. However, you can also select Para-EQ mode, which
means using sharp parametric EQ sections to remove the fundamental and harmonics. Generally,
if the buzz contains many harmonics, or if the frequency of the buzz is wandering, it is best to
use the Comb filter. If there are only one or two harmonics to remove, then you may find that
you prefer the sound of the parametric EQ filters.
The Comb filter has equal width notches when viewed on a linear frequency scale, which means
that the notches will be narrow at higher frequencies. For removing a wide-band buzz that has a
low frequency fundamental the Comb filter will do least damage at HF.
For similar settings of fundamental frequency and Q, the Para-EQ filters will be narrower at LF
than the Comb, but will widen as the harmonics and frequency increase and at HF will be wider
than the equivalent Comb filter section. With parametric EQ filters, the notches have equal
width when viewed on a log frequency scale, but when viewed on a linear scale they will appear
to widen as the frequency increases. This means the notches will tend to merge together at higher
frequencies, so this is not recommended for removal of wide-band buzzes as it is likely to cause
unnecessary damage to the original audio.