By “carving up” this choir microphone with medium bandwidth EQ filters, we have drastically changed to the tonal characteristic of the choir sound in the process of increasing GBF.
We’ve taken away big chunks of the sound we would probably like to hear! Yes, it is louder (without feedback), but it may sound really rough.
Wouldn’t it be nice if we could reduce the gain on only the narrow feedback frequencies without affecting much of the ranges just above and below them?
It is clear that we would benefit from cutting with EQ filters that are much narrower, and placed exactly on the feedback frequencies.
What is needed here is simply good parametric EQ. Some fine mixing consoles have fully parametric equalizers on each channel strip, but many do not. Some simply have fixed-frequency EQ, while others feature “semi-parametric” or “quasi-parametric” EQ. There is a big difference.
Fully parametric EQ allows us to adjust three parameters: the filter’s gain (cut or boost), the center frequency and the Q (bandwidth). Fixed frequency EQs have a pre-selected and permanent center frequency and Q.
They are somewhat useful for tonal shaping, but don’t allow the operator to adjust the frequency or bandwidth of the filter—they are far less than ideal for feedback filtering.
Still, a number of consoles employ fixed frequency EQs for the low and high filters, and then feature a semi-parametric midrange control. But again, for notching feedback, we require control of all three filter parameters described above.
So in that first example where we cut the high-mid frequency down, a parametric EQ would have allowed us to do this:
Note that the range of frequencies affected by this filter is considerably smaller than the original broad cut we made at the same frequency of 5 kHz.
If we use similarly narrow filters for those next ring tones (250 Hz and 1 kHz), the final result of our effort looks like this:
Big difference as compared to the original result with broader filters!