Specifications

5.1-Channel Production Guidelines Production Techniques
5-6
In theatres, the LFE channel is used in conjunction with subwoofers to supplement
the capabilities of the screen speakers. In most music productions, it is unlikely there
will be a technical need to use the LFE channel. Since the overall program level may
be adjusted to render any proportion of bass perfectly, the LFE channel might be an
advantage only in situations similar to the famous cannon shots in Tchaikovsky’s
1812 Overture. In such a case, the overall program level might have to be reduced
several dB just so the last few minutes can make the desired impact without overload.
By using the LFE channel, the orchestra can be recorded at a normal level, with some
of the loudest, deepest bass of the cannons carried in the LFE channel. Of course, the
main channels will still carry the cannon shots so that they will be heard from the
appropriate locations and in a downmix.
Another benefit to using the LFE channel when carrying explosive bass signals is that
smaller stereo systems may not be able to handle such high levels of deep bass without
significant stress. Since the Dolby Digital downmix process discards the LFE signal,
these low-frequency signals will not present any difficulty for these smaller systems.
The remaining portions of the bass frequencies delivered by the main channels will
convey the essential aspects of the performance when listening to the downmix.
While it may be of no particular consequence for effects, filters like those used in
generating the LFE signal may interfere with the ability to seamlessly blend the LFE
channel with the other channels. The best way to ensure a cohesive audio signal across
the entire audible spectrum is to maintain its integrity in the main channel(s).