Specifications

5.1-Channel Production Guidelines Introduction
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possible to reproduce a higher quality of sound in the cinema, it was still not easy to
deliver or reproduce strong bass. The best soundtracks of the day (70 mm magnetic)
had reached their maximum recording capability, so it was impossible to increase the
bass without causing overload. Even today, the main screen speakers used in cinemas
do not reproduce below 30 Hz, so if the soundtrack carried more bass to the
amplifiers, it would not necessarily be reproduced.
To increase low frequency playback capabilities, subwoofers were installed in the
cinema. To direct bass signals to the subwoofers, a separate channel was added to the
soundtrack. Known as the LFE channel (for Low Frequency Effects), it handles bass
created specifically for subwoofer boom effects and may also carry low frequency
information from the other channels in order to enrich the overall soundtrack.
A consumer delivery format like a CD is significantly different from a cinema
system. CD loudness is not calibrated—the consumer decides where to set the volume
control. Nor is the CD recording level calibrated—a music producer may add more
bass to a recording by adjusting the overall levels thus ensuring that the additional
bass will not cause overload.
In a similar manner, each channel in the Dolby Digital system can carry bass content.
So why is there an LFE channel in a consumer audio delivery format? Quite simply, it
allows movie soundtracks to be transcribed directly and without alteration to the
home video format. This does not mean the LFE channel should not be used. It
suggests that the LFE channel may not be the only, or the best way to provide loud,
deep bass. This becomes more apparent when one actually mixes multichannel audio
using a properly configured and calibrated studio monitor system.