Thanks Blink,
So, I just need to duplicate one of my tracks and make it an LFE setting. I did notice if I made one of my normal tracks, an LFE track, the LFE VU meter then worked. I don't remember reading anything about having to duplicate a track to get the LFE, so I'm still stumped.
If you mix in two different sources for the LFE, do you get phase cancellation? Wondering if it thins out the bass doing it that way, when mixed to one track.
The other thing I'm not sure about is I thought the center track was supposed to be for speech, which wouldn't have very many low frequencies.
I was really under the impression that the LFE would be automatically created from the existing tracks by just dividing the frequencies and making the existing tracks not go below 120Hz and then sending all the lower frequencies to the LFE track, but that's not happening.

First the LFE track (contrary to popular belief) is not actually part of the Dolby spec, but none the less it is treated just like any other track. In other words if there is no sound contained withing the track, then you won't see anything on the VU meter. If you remove the sound from the left/right front track then the front VU meter will no longer show anything.

But because the LFE track is not part of the spec, what is on the center channel also goes through the LFE channel, so as long as you have a center channel that contains all (or most of the sound for you video) then you will get LFE regardless as to whether you include a LFE track. If you are not using a center channel then you must include a LFE track so that your low frequencies don't get left out.

For example I put background music on my front and rear channels (with a bit of delay between the 2 for depth), but the back ground music is not on the center channel (only the actual video soundtrack), so I have to include a LFE track for the BKground music so it is included in the LFE track. But I do an LFE track regardless of what channel(s) i'm using anyway.

Yes the center channel is used for speech but it works much the same way as the LFE.... it mixes the left and right for a mono track and uses a center band pass filter. In otherwords the tracks are the same (and full spectrum)... only different filters applied.

Phase cancellation only takes place when you mix 2 EXACT same signals that are 180 degrees out of phase (opposite from each other). Mix any other signals and the result is additive (unless you actively set a subtractive mix). Now you can get DEGREES of cancellation if you're not careful. Two exact same signals occurring at the same time at the same amplitude will TOTALLY cancel each other out A signal with an amplitude of one mixed with a signal with an amplitude of -1 will equal 0 (1-1=0). But if you mix different amplitudes.... 2-1=1. But again the signals have to occur at the same time and they have to be out of phase from on another..... possible.... yes.... but not very probable on a sound track.

There is lots of info here - [url=http://www.dolby.com/resources/tech_library/index.cfm] (select 'Dolby Digital (AC3)' in the search menu).

You don't have to have anything on the LFE channel - the other channels are full frequency range anyway. When DD5.1 is downmixed to stereo or pro-logic in the DVD player the LFE is discarded anyway, so don't put anything on LFE that you can't afford to lose since people listening in stereo won't hear it anyway.

The other thing to be aware of is that the LFE channel level is boosted by 10dB on playback by the AC3 decoder, so you need to take this into account when setting levels in Vegas. (It's so you can have really LOUD LFE to go with your earthquake scenes :-)

AFAIK, in Vegas the FL/FR/SL/SR/C channel outputs just get passed to the AC3 encoder 'as-is', the LFE channel has an optional low-pass filter but is otherwise passed unchanged - there is no linkage between channels or automatic creation of 'derived' center/LFE outputs.

Tony

A related concern with which I've wrestled is how to set the volume of the subwoofer monitor in your studio. If you don't get this at least in the ballpark, your low-frequency material can play back way too high or low in the final project.

Does anyone have any insights here?

LFE is *not* a copy of the center channel. It is designated for low frequency effects only (hence, "LFE") - the low end of explosions, cannon blasts, etc, etc.

The confusion is that playback systems will have a sub, and that will carry low frequency content from all tracks based on the crossover for that system, not just the LFE (which will usually also go to the subs as well).

The way to mix for surround is to have a bass management system that separates low end to your sub so you hear music with low end, but allows you to treat the LFE as an effect channel, not low end for music, etc.
Ideally, the 5.0 system should be full range and not dependent on subs for low end, esp. if mixing for theater.

In Vegas, if you want to send to the LFE for enhancing effects as you would an aux or effect, I think you would have to setup a separate buss to route to as a send from a track, then assign that to the LFE (vs. assigning tracks to LFE only, which sends them to LFE completely). In Nuendo (and ProTools) we can send to the LFE in percentages, so we don't have to split out tracks - i.e. some effects will be full range, with a little sent to the LFE for extra impact.

Use the LFE for occasional high impact effects, but not to make the music's bass response stronger. Depending on the type of project, you may rarely use the LFE.

Regards,
Dedric

To set levels for mixing with a sub, you need to go through Dolby's process for adjusting levels with a pink noise file (Dolby and BlueSky both have files for use). You need a level meter to set each. This test includes a way to set the sub as well. Note though, if your room isn't treated for even bass response, this setting could still be off by a little, or even quite a lot.

Well, if it's designed mostly for effects, then that makes the decision easy.
No LFE. This is just music.
Thank you everybody, for your input.
kdm, I think your explanation sounded most likely
If the low end will still get transferred during playback from the 4 corner channels, that may be a better way to ensure the volume for the bass frequencies is set right.

If anybody has a different opinion, I'm still listening.

"If anybody has a different opinion, I'm still listening. "

Wendy Carlos's pages on surround sound is a pretty good starting point. It seems to me that ignoring the centre channel might defeat the whole point of 5.1.

A lot of the confusion about the LFE channel seems to come from the advent of those 2.1 setups for gaming.

Bob.

Hi TGS - that is correct - what you mix for the front and surrounds will be distributed to any subs via crossover, just as a stereo system with a sub would for a stereo CD. Fwiw, I do audio post for a living, so this info is both from experience and industry standard practice to ensure the decode sounds as you intend at playback on different systems, but for more info, in addition to farss' and owlsroosts' links, here's a specific link to a music mixing doc in the Dolby library owlsroost suggested (see chapter 5) - more docs in the AC3 section are worth looking through: http://www.dolby.com/assets/pdf/tech_library/4_Multichannel_Music_Mixing.pdf.

Here Dolby does suggest the option of using the LFE for bass control/enhancement in music-only settings. But if this is a film/video for DVD or theater vs. pure music DVD, film conventions would be different than, for example, a music concert video mix might be. My advice is based on the assumption you are working on a film with music (where LFE is effects almost exclusively), rather than a music-only project as described in the above pdf.