Digital compression systems currently used for broadcasting surround sound for television include an extra audio channel specifically for the purpose of carrying high level, low frequency sound effects. This channel is commonly referred to as the "LFE". There is some debate about its usefulness in normal broadcasting, and there is much confusion about how it should be used, particularly when the concept of a sub-woofer is brought into the system.

The purpose and properties of the LFE channel found in broadcast systems are described, in isolation from sub-woofers. The addition of a sub-woofer to an audio system, without reference to LFE is also described. Ways in which the two can be combined in a single system are then shown, highlighting the numerous ways in which this can be done incorrectly. Some of the problems that make it difficult for the audience to ensure that their system is working optimally are shown.

The conclusion drawn is that use of the LFE should be limited, it it is used at all.