Filter
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6-5
DFP-3000
40 63 100 160 250 400 630 1K 1.6K 2.5K 4K 6.3K 10K 16K
Center channel loudspeaker response
40 63 100 160 250 400 630 1K 1.6K 2.5K 4K 6.3K 10K 16K
Digital subwoofer (LFE) channel response
10dB higher SPL
This procedure, which requires an RTA, matches the playback gain of the SDDS Preset’s
subwoofer loudspeaker in the cinema to the playback response of the digital subwoofer (LFE
loudspeaker) on the stage where the film’s sound track was mixed.
When evaluating the SDDS digital subwoofer (LFE) level, no listening test is entirely definitive,
because the amount of energy in the LFE channel is a creative decision made when the
soundtrack of each film was mixed. For the same reason, the digital subwoofer (LFE) low pass
filter setting has no relationship to the screen loudspeakers’ performance. It merely serves to
exclude undesirable sound from the subwoofer (LFE) cabinet. The actual sounds reproduced on
the digital subwoofer (LFE) channel are determined by what was put there by the film’s sound
mixer, as long as the filter frequency is not set so low as to remove sounds the mixer intended to
be included. Setting the digital subwoofer low pass filter frequency to 100 to 200 Hz should be
acceptable and either setting should sound the same when actual film is exhibited; start with 160
Hz. Subwoofer manufacturers may have specific recommendations for their cabinets.
Note that the result of a wideband SPL measurement of pink noise from the SDDS subwoofer
(LFE) will depend on both the level Trim setting and the low pass filter Frequency setting. For a
LPF frequency setting of 100 Hz, a wideband measurement made with an SPL meter will show
approximately 91 dB. Such a measurement should only be made to confirm that a correctly
calibrated theatre has not drifted, and cannot be used as a primary calibration measurement in
place of an RTA. Also remember that the analog subwoofer channel trim is effectively in series
with the subwoofer amplifier’s input gain control. This means that an adjustment to the analog
subwoofer channel trim also affects the playback level of all digital subwoofer signals.
6.10 When adjusting the SDDS subwoofer (LFE) level offset, the SDDS Preset must be made the
active Preset. Select the preset manually with the Active Preset option under the Presets item in
the main screen menu bar and then selecting the SDDS Preset, or by clicking the appropriate
radio button at the lower left of the main screen.
8 is the default preset for SDDS. Press F6 to manually the subwoofer output channel. Alterna-
tively, the software will automatically select the SDDS Preset when you have selected the
Subwoofer output channel and click the SDDS Subwoofer Offset slider.
Use the SDDS Subwoofer Offset slider control and
your real time analyzer (RTA) to set 10 dB of in-
band gain of the subwoofer’s bands as compared to
the previously calibrated Center speaker’s bands in
the region of its flat frequency response. Be sure to
allow extra time for the low frequency bands to
settle to their final values.