User manual

miniDSP Ltd, Hong Kong / www.minidsp.com / Features and speci fications subject to change wi thout pri or noti ce 46
6.4.3 LFE gain structure problems
The difference in signal levels noted above for Custom Configuration is likely not a problem in practice, in most
systems. If, however, you do experience issues with distortion on the subwoofer channel at high playback levels,
it may be that you are clipping the subwoofer output of the source equipment or the subwoofer input of the
DDRC-88A. Here are two possible remedies:
 Reduce the level of the subwoofer trim in the source equipment and
increase the gain on the subwoofer amplifier by the same amount. If you do
this, you will need to remember to set the subwoofer gain back to its
previous position if you redo your Dirac Live calibration.
 Remove the 10 dB alignment gain from the source equipment completely,
and use the 5.1 Speaker System or 7.1 Speaker System configuration. If
your source does not have a 10 dB gain switch/setting, you should be able to
accomplish the same thing by setting the subwoofer trim control to −10 dB.
You will need to redo the gain structure optimization procedure on page 42
and your Dirac Live calibration as described in sections 3 and 4.
6.4.4 Bass management and LFE alignment gain
When redirected bass from the speaker channels is mixed with the LFE channel, it is mixed at a relative level of
−10 dB. After 10 dB LFE alignment gain is applied to the mixed signal, the redirected bass is at the correct level
again. The whole discussion above therefore applies regardless of whether the subwoofer output from the
source equipment is carrying only the LFE content, or bass-managed content that includes the LFE content
mixed with bass from the speaker channels.
If mixing of redirected bass is performed digitally, there is a danger of clipping the signal. The LFE signal already
uses the full-scale digital range, so adding in bass from another seven channels, even reduced by 10 dB, could
exceed the maximum digital signal level. To avoid this, the LFE is reduced prior to mixing by 5 dB and the
redirected bass from the speaker channels is reduced by 15 dB. After D/A conversion, 15 dB of gain is applied in
the analog domain (10 dB alignment gain, plus another 5).
Some consumer equipment, however, does not apply the 15 dB of analog gain. This is more likely in front -end
equipment like DVD/Blu-ray players. If a unit like this is connected directly to the DDRC-88A inputs and bass
management is used, you will need to:
 Use the 5.1 Speaker System or 7.1 Speaker System configuration for 10 dB of LFE alignment gain, and
 Add another 5 dB of gain by:
o Raising the subwoofer trim level in the source/processor by 5 dB, or
o Adding 5 dB of gain in the subwoofer amplifier after completing Dirac Live calibration.