Sound Performance Lab 2595 - Manual (Page 14)

14
Passeq
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LF-LMF Cut and LF Boost
The low cut frequency range extends from 30 Hz to 1.9 kHz and will be ref erred to in this text
as LF-LMF (Low to Low-Mid frequencies ). In con trast, the low boost (LF Boost) band en com-
passes a range of 10 Hz to 550 Hz. The maximum available in crease in this LF boost band is
(+)17 dB, while the maximum reduc tion of the LF-LMF cut band is (-)22 dB.
Optically these filter bands may be represented as having a shelving characteristic with an
6 dB slope. Passive filters do not allow for direct alteration of the slope gradient because this
quality is pre-determined by component selection and not, as with active filters, by a vari-
able value.
The lowest frequencies begin here with 10 Hz, then follow with 15, 18, 26, 40 Hz, and so on.
At this point one might think that such a lavish set of frequency choice in this range might be
a bit overdone, as there is acoustically a rather limited amount of audio material of any real
significance below 26 Hz. However, these choices are anything but arbitrary. These frequen-
cies represent a consistent -3 dB point of a sloping down response curve. That is, the gentle
6 dB slope also allows frequencies above 10 Hz to be processed. As mentioned in other parts
of this text, special condenser/coil/resistor filter networks have been designed for each
frequency range. The choice of one or the other inductances produces differences in sonic
coloration even when limited differences between frequencies such as 10 Hz or 15 Hz play a
subordinate role. Along with this differing phase relationships may come into play and affect
tonal color. Because modern productions often demand a definite number of choices in an
engineer’s options for achieving an optimal result in bass emphasis, the Passeq has been
designed with a very complete set of low frequency options to insure realizing these goals.
MF-MHF Cut and LMF-MHF Boost
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 characteris-
tics, 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 filter‘s compo-
nents for a maximum in musical efficiency, relying in the Passeq on its developer, Wolfgang
Neumann‘s years of musical experience. The middle bands‘ peak structure 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 resulting undesirable influ-
ences 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.
The MF-MHF cut band overlaps the LF-LMF cut band by approximately an octave, with its
lowest frequency extending from 1 kHz. The LF boost and LMF-MHF boost bands are set up in
a similar fashion, with the lowest LMF-MHF boost band frequency set at 220 Hz and thereby
1-1/2 octaves under the highest LF boost band frequency. The maximum values of the MF-
MHF cut and LMF-MHF boost band extend from -11.5 dB to +10 dB.
The overlapping band characteristics give a good idea of the available degree of precision
in frequency adjustment: For example, one can boost in the LMF-MHF boost band at 220 Hz
while in the LF boost band, 240 Hz can be followed by 320 Hz in the LMF-MHF boost band: The
next step could be at 380 Hz in the LF boost band, followed by 460 Hz in the LMF-MHF boost
band and 550 Hz in the LF boost band ...
Operational Elements
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