Specifications

5.1-Channel Production Guidelines Production Techniques
5-5
film industry so well also applies to multichannel mixing: Use the surround channels
to enhance rather than distract from the overall experience.
5.3.3 LFE Channel
What is the difference between the LFE channel and the subwoofer signal? The LFE
channel is a separate, limited frequency bandwidth signal created by the mixing
engineer and delivered alongside the main channels in the mix.
The subwoofer signal is created in the decoder as needed for the particular speaker
complement in use, using crossover filters. This signal is created using bass
management, and all Dolby Digital decoders perform this function. Through bass
management, a subwoofer signal may comprise bass from any channel or
combination of channelstypically bass frequencies from channels being replayed
on small speakers are directed to the subwoofer speaker. If no subwoofer is present,
the bass (including the LFE channel, if it exists) is redirected to the speaker(s) best
able to reproduce it, usually the main stereo pair.
Even though an eighth-order, 120-Hz brickwall filter can be applied to the LFE
channel by a Dolby Digital encoder, a low-pass filter must be inserted into the LFE
signal path during the mix process to ensure proper monitoring. Furthermore, the
filter must be applied to the signal being recorded so that the results will be
consistent, whether delivered by Dolby Digital or Linear PCM. A maximum cutoff of
80 Hz is suggested when using a typical filter with a gradual slope as compared to the
steep, low-pass filter in a Dolby Digital encoder.