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APA-4E8 Operator’s Manual Page 63
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Appendix I: Dynamic EQ
Dynamic EQ is essentially a compressor or expander that can be set to respond and act upon
only a certain range of frequencies. Its behaviour is dependent on the operating mode
chosen: the operating modes are explained in detail below.
Mode I: “Cut Above”
Having selected the frequency band to work with, the dynamic eq will listen to this band and
act upon it by cutting (compressing) any frequencies present in it that go above the
predetermined threshold. Consider the example below where the threshold is set to —20dB,
and the selected frequency band is centred around 1kHz, with a ‘Q’ of 1.0.
Signals below the threshold will pass unaltered, but as increasing signal is applied, those
frequencies centred around 1kHz will be cut or compressed. The ratio in the above example
is set at 2:1 so, as with any compressor, the amount of gain reduction applied depends on how
much the signal exceeds the threshold. The
red line represents a signal at 0dB, which is
20dB above the threshold. At 1kHz, therefore, the signal has been compressed to —10dB or
2:1.
Uses of “Cut Above” mode
Traditional use of ‘frequency conscious’ compression is to control or ‘tame’ a certain band of
frequencies within the program material. Insertion of EQ into the sidechain will make the
compressor respond to the required band, but it will cause broadband compression of the
signal, so any peaks will cause the entire signal to be compressed. This produces the
familiar problem of dulling the material if it is bass-heavy, or causing unnecessary dips and
changes in ambience when attempting to remove sibilance. The difference with dynamic EQ
is that only the band selected is compressed. This means that it becomes possible to
compress the low frequency content of material without affecting the high frequencies at all.
The result is increased volume and perceived level without sacrificing clarity. Any instance
where the desired result is to control a band of frequencies, such as de-essing, or de-
popping, without affecting the surrounding frequency ranges is an ideal use for this mode.
Controlling LF spill and bleed in situations where it’s desirable to maintain perceived level
without causing environmental noise issues can also be achieved with use of a dynamic LF
shelf in “cut above” mode with long attack and release times, Try de-essing with the filter
centred at 8-9kHz, and a relatively narrow ‘Q’ of about 4, attack 1mS, release 100mS.