What Does LFE Stand For?

You may have heard the initialism LFE, but what does it stand for? And what relevance does it have to your surround sound or immersive audio speaker system? In this article answer your questions about LFE and the meaning behind the term.

What Does LFE Stand for?

LFE stands for Low Frequency Effects, and refers to a channel in a surround sound or immersive audio setup that handles frequencies below approximately 120Hz. The LFE channel in these types of setups are usually sent to a subwoofer, designed to reproduce bass and sub-bass frequencies with the highest accuracy possible.

What Does the LFE Channel do?

The LFE channel was designed to deliver bass-only information to supplement the overall bass content. It's important to understand that the LFE channel content is not the same as the content of a subwoofer output found on many home theatre systems. The LFE channel is intended to carry additional bass information in the surround sound programming, while the subwoofer output is bass information from up to all six channels that has been selected to be reproduced by the subwoofer via a bass management system. Beginners often get confused between the role of the LFE channel and bass management, in which monitor systems use the subwoofer speaker to achieve two roles.

It is important to understand that the LFE is a specific content channel and that it’s actually a 120Hz bandwidth-limited channel. It also has an additional 10dB of electrical headroom compared to the other main channels. Its purpose is to add content-specific low-frequency energy, and because it is an effects channel, it should only be used for effects rather than musical or dialogue-based content. This ensures that consumers will appreciate systems that have LFE reproduction, but the same mix will still hold together on other systems without it.

Considerations of Using an LFE Channel

If you put content other than low-frequency effects through the LFE channel, such as musical elements, then you run the risk of encountering phase misalignment in your bass management path. This may cause phase cancellation and therefore a reduced level in low frequencies, or may cause phase doubling which can result in a speaker system overload. Additionally, because the LFE channel is calibrated differently on different systems and the crossover frequency may be different, it is very difficult to check your mix will translate if you use the LFE channel to enhance other content.

Finally, it is recommended not to put anything critical to the mix exclusively in the LFE channel. This is because when the audio is folded down to stereo, the LFE channel is usually dropped completely, and so any content routed to the LFE channel won’t be reproduced when the fold-down mix is used. This way, as long as the LFE channel is only used to enhance very low-frequency effects then their removal from fold down mix is not catastrophic to the mix.