SPL Passeq, Manual

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13
Control Elements
MF+ and MF-
The midrange bands elevate the PASSEQ to a complete combination of filter options that
classic passive designs do not offer. Both midrange bands exhibit peak filter character-
istics, that is, when viewed from the boost band, the frequency curve appears as bell-
shaped slopes above and below the chosen frequency range. The slope or Q-value is,
again, not variable, but attuned through the choice and configuration of the passive fil-
ter‘s components for a maximum in musical ef ciency, relying in the PASSEQ on its devel-
oper, Wolfgang Neumann‘s years of musical experience. The middle bands‘ peak struc-
ture is chosen for a clean separation of LF and HF bands. Were the choice here to be for a
shelving filter design, too many neighboring frequencies would be processed, with result-
ing undesirable influences extending into LF and HF bands. Along with this is the simple
fact that a midrange peak filter characteristic is accompanied by a more easily focused
center point processing of critical voice and instrument fundamental frequencies.
HF+ and HF-
PASSEQ’s high frequency bands have a different layout for the cut and boost ranges: The
HF- cut band exhibits a (wide-band) shelving characteristic, while the HF+ boost band
exhibits a variable Q, peak filter characteristic.
As seen above, one can also note and intensification in choice of frequencies in the
high range. Here the same reasons apply as in prior cases: Individually designed and
constructed coil-condenser-resistor configurations result in slightly differing sonic
characteristics.
Q (HF+ Band)
Like already mentioned in the last chapter, with the HF+ Band you got the possibility to
change the Q-factor (value), thus the bandwidth, thanks to the Q-control. The control
range here ranges between 0.1 Q and 1.0 Q. Again all settings can be adjusted through a
41 step detented potentiometer.
With the proportional or variable Q principle, boost control settings would apply only if
the HF+ Q were to be set at Q=1.0 (control set fully clockwise). Were the value to be re-
duced (thus increasing the bandwidth), the boost would also be reduced. This can lead to
a situation wherein, for example, a HF+ Q setting of 0.1 and a boost of 3dB would result
in effectively no audible boost in the chosen frequency—at this value the Q value resides
at about 0.3dB. With this Q value, don’t hesitate to turn turn up the HF+ band boost con-
trol to its full 12.5 dB setting—this results in an actual overall increase of around 3.5 dB.
Narrower Q settings, for example, to 0.6, result in further level boosts again. The advan-
tage of a Proportional-Q design compared to Constant-Q design rests with the musically
superior way it functions. The acoustic energy below the bell-shaped curve remains es-
sentially the same and thereby it retains the balance of high frequencies in relation to the
entire frequency spectrum while experimenting with different Q values. While it is true
that one must think independently of the scaled gain dB values of the HF+ boost switch
in such cases (because these only apply to a Q value of 1), the result is a simpler, more
musically sensible and worthwhile way to work that does not require continual additional
corrections of the Q values.