The Subwoofer and LFE Channels Defined (Part 2 of 2)
In addition to the Low Frequency Effects information carried in the ".1" channel of a multichannel audio signal, the subwoofer installed in most consumer systems is also used for a process called bass management. This process enables consumers to use smaller satellite speakers for the left, center, right, and surround channels by diverting their low frequency information, which they likely cannot physically reproduce, to the subwoofer that can reproduce them.
A form of bass management called bass extension was once again pioneered in cinema to extend the frequency response of the main channels by utilizing the low frequency capabilities of a dedicated subwoofer. This meant that the main speakers could concentrate on reproducing the majority of the audio spectrum, while the subwoofer filled in the bottom end. Most home theater systems rely on similar techniques. This can be observed when initially setting up such a system when it prompts users to select the size of the main speakers. The correct answer is usually "small" as most home theater speakers are not capable of accurately reproducing audio below 120 Hz. Selecting the "small" option filters out the low frequencies from that channel and routes them to the subwoofer. This seems to be the default setting chosen by manufacturers of such systems, so even if a consumer has not made the selection, chances are it has been made for them.
With bass management on, the filtered low frequency information from these channels is combined with audio from the dedicated LFE channel and the sum is sent to the subwoofer. This means that even if there is nothing present in the LFE channel, it is almost guaranteed that there is still low frequency audio coming from the subwoofer by virtue of bass management. Beware then of complaints about missing LFE channel--it may just be that the ".1" is not enabled and not that any audio is missing.
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