L-Acoustics V-DOSC, Operator'S Manual

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L-ACOUSTICS V-DOSC Manual Version 4 6/29/2005 Page 125 of 158
as straightforward and the best results are obtained subjectively. Predelay can be applied before
or after performing the detailed measurements outlined in the following section – just be sure that
the correct relative delay is also applied to subwoofers, fill systems and downfill systems.
Finally, many users have reported good results when using program compression/limiting on the
main mix, i.e., before the digital processor inputs. Using a high quality compressor/limiter (eg SSL,
dbx 160S, XTA SIDD or other high quality equivalent) and a moderate amount compression, e.g.
1-2 dB with a 1.5:1 to 2:1 ratio, allows the mix to ''sit better on the system'' and prevents
transients from ''jumping out of the mix''. In addition, calibrating limiter threshold to the digital
processor clip point provides an additional level of system protection by preventing digital clipping
of the processor inputs. Program compression/limiting before the processor inputs also provides
another level of control when dealing with ''over zealous'' guest engineers in a festival situation…
5.2 MEASUREMENT PROCEDURES
Tuning and equalizing V-DOSC is relatively straightforward, i.e., given the prediction tools and
sound design concepts outlined in Chapters 2 and 3, the precise installation procedures described
in Chapter 4 and dedicated OEM factory presets, an excellent starting point for system tuning is
immediately obtained upon installation.
Generally speaking, little equalization is required and one third octave real time analysis (RTA) can
be sufficient for measurements. Alternatively, MLSSA, WinMLS, TDS, SMAART or Spectrafoo
analysis can be used to obtain higher resolution and for time alignment measurements.
When properly installed and focussed, system coverage should be very homogeneous and 3
measurement locations are sufficient for performing a systems check: one in the near audience
area, one at the mix position and one towards the rear of the coverage pattern. It should be
verified that the global shape of the frequency responses at these locations is similar before
proceeding to perform detailed equalization.
Measurement Instruments
Equalization adjustments can be performed using a real time analyzer (RTA), however, more
sophisticated measurement tools such as MLSSA, WinMLS, TDS, SMAART or SpectraFOO allow
the user to obtain better results (provided these instruments are properly used, of course).
Compared with RTA measurements, improved frequency and time domain resolution can be
obtained and time windowing is useful for eliminating room reflections from measurements – i.e.,
in general, the goal is to eq the system so that the direct sound is as flat as possible for the
mid/high section while obtaining the desired sub/low spectral contour. In addition, impulse
response measurements that can be performed using MLSSA, WinMLS or TDS are highly
recommended for time alignment of subwoofers (see Section 1.15 for guidelines) and time aligning
delay plus fill systems (in terms of accuracy and the time required for performing measurements).
It is often useful to perform room measurements throughout a given array’s coverage region (9-12
measurement locations) then perform a weighted spatial average to determine a spatially averaged
response curve. The spatially averaged frequency response is then inverted and used as a target
for adjusting the system equalizer (which is swept electronically using the measurement
instrument and adjusted to meet the target curve). Alternatively, the system equalizer can be
swept electronically while it is initally flat. Multiplying the flat eq curve by the spatially averaged
curve then allows you to adjust the equalizer while directly monitoring the effect on the spatially-
averaged response. These techniques can be used for fixed installations (where system equalizers
are remotely located) or for touring applications – the advantage is that eq adjustments can be
performed “offline” and it is not necessary to make excessive noise during the system eq process
(which can be disruptive to other people working on the installation).
Note: For 5+1 format presets (V-DOSC INFRA, X, 4W), fullrange ouput 5 (input A) can be used to
monitor the effects of input parametric equalization which is used for system eq.