This article provides you with a brief overview of how the LFE channel is managed in Wwise. Some background information is also provided along with some best practices for LFE and bass management, in general.
To feed the LFE channel in Wwise, you need to import a file that has one of its channels tagged as LFE. Currently, the following channel configurations are supported: 0.1, 1.1, 2.1, 3.1, 4.1 and 5.1. Once imported into your project, you can control the volume of the LFE channel using the LFE volume slider in the object’s Property Editor. Effects can also be applied to the LFE channel using the “Process LFE” control that is available in the Effect Editor of most of the effects in Wwise.
We made a conscious decision to enforce an independent LFE channel instead of using the LFE send method, which sends the signal from the main channels to the LFE channel. Our decision was based on the best practices suggested by prominent organizations in the audio field, such as Dolby and The Recording Academy's Producers & Engineers Wing.
According to these organizations, routing audio from the main channels to the LFE is not recommended because consumer decoders will often sum the LFE and the redirected bass from the main channels during the decode process. This can produce a series of anomalies, ranging from “doubling energy” present in the subwoofer to phase cancellation[1] induced by delays present in the overall signal delivery system. Although any of these anomalies may result, the most frequent problem encountered while using the LFE send method still remains comb filtering anomalies. By adopting a method that uses an independent LFE channel, Wwise avoids these types of anomalies.
According to one industry insider[2]:
The best way to use the LFE channel is to route unique bass signals to this channel that is different but compliments the signal routed to the main channels. […] It is always important to remember that the Dolby Digital downmix process discards the LFE signal, and the LFE signals will not be present for users listening on two channel stereo systems. Therefore, it is critical that any essential audio in the LFE channel be complimented (not replicated) in the main channels.
This LFE signal can be created in a variety of ways, a few of which are listed below:
- Add several sine waves that are not harmonically related and below 80Hz.
- Process a similar sound effect with an 80Hz low pass filter.
- Extract from an LFE sample CD.
Using various settings on an ADSR envelope, a single LFE signal can be reshaped to compliment a variety of sound effects. As a result, a small library of standard LFE signals may be sufficient for most applications.
We hope this article helps to demystify LFE usage in Wwise and will help you in your production.
[1] Producers & Engineers Wing Surround Sound Recommendations Committee (2004). Recommendations for Surround Sound Production (p. 3-9). Los Angeles, CA: The National Academy of Recording Arts & Sciences. [Retrieved February 27, 2009, from http://www.aesnashville.org/PDFs/NARAS/5_1_Rec.pdf]
[2] Unfortunately, we have lost the reference of this text during our internet researches. Our apologies to the author(s) and be assured that we are still looking for it. The necessary modifications will be made as soon as the source will be found.
