Sound Performance Lab 2595 - Manual (Page 23)

23
Passeq
Equalizer
In our context here, an EQ is in effect a network of frequency filters which changes its output
characteristics depending on frequencies. The common recording studio concept for sound
shaping or correction is the amplitude-based EQ. But owing to the large number of filter
combinations, there are practically too many existing formulations of this design concept
to count. Nonetheless it is sensible to make some general observations that categorize the
most important technical differences among these design concepts.
Passive EQs
The filters in a passive network employ no intrinsic amplification elements and therefore
need no external power, which means in effect that they can really only cut the energy of
a chosen frequency. In order to expand this capability to include boosting the energy of a
bandwidth (that is, to be able to boost and cut frequencies), the overall filter input signal
level is reduced. Based on this overall reduction and relative to the original input signal, one
can achieve a further cut or boost in the form of a return to that original signal level. Thus
a passive filter is always followed by an amplifier which is responsible to regain the initial
energy reduction and restore level balance between the input and output signal levels.
Passive filters react differently than active filters, mostly due to the saturation and loading
characteristics of its coils and condensers. The characteristics of passive filters often are
very advantageous in their ability to create a musically pleasing sonic result: they sound
comparably very smooth and harmonious (please see “Introduction—Advantages of Passive
Filter s” on page 5).
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The Basics of Frequency Filtering
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Schematic of a passive frequency
filter
Block diagram of passive filter
set flat
Block diagramm of a passive
filter at +18 dB boost