Creating Surround Sound LFE tracks correctly

Berty wrote on 7/15/2018, 9:32 AM

I am trying to burn my surround sound project to disk.

If I render using "Sony AVC/MVC - AVCHD 1920x1080-501 5.1 surround I get an M2TS file with all the tracks separated correctly. Only things I have put on the LFE track are on the LFE track. Lovely.

But I want to create a DVD and a BluRay disk of this.

Magix have told be to create two files to do this - a video file and an audio file.

If I create using Mainconcept MPEG2 - DVD Architect PAL Video stream, I can create an mpeg file for the video. I then create a Dolby Digital AC-3 5.1 Surround file for the audio. I can then use DVD architect to burn these to a DVD.

All the tracks are separated correctly except the LFE. This seems to have had a low pass filter applied, so that bass from all the audio tracks is on it (possibly with the addition of anything I put on the LFE track - it's difficult to tell). This is not what I want as some of the vocals which are on the centre channel can be a little boomy when coming through the subwoofer.

In the properties for the project I have turned off "Enable low-apss filter on LFE" which surprisingly made no difference (more surprisingly if I create an M2TS file with this setting on then I don't get a low pass on my LFE track - I still only get what I specifically put on the LFE track which I would have thought was wrong).

Anyone got any experience of this ??

Maybe this is a decoder issue as if I play the m2ts file on my PC (which has a 5.1 sound card) then I can hear bass even when I can see that the LFE track is empty. Maybe my DVD and BluRay player are just doing that ??

Also - how can I create the video for the BluRay - the "Mainconcept MPEG2 - DVD Architect PAL Video stream" gives an error if I just up the resolution to 1920x1080 from the default DVD settings.

Using Vegas PRO 15 and DVD Architect Pro 6.0.

Thanks in advance......

Berty

Comments

Former user wrote on 7/15/2018, 9:38 AM

 

Also - how can I create the video for the BluRay - the "Mainconcept MPEG2 - DVD Architect PAL Video stream" gives an error if I just up the resolution to 1920x1080 from the default DVD settings.

 

You need to use the Bluray templates, not DVD templates.

Berty wrote on 7/15/2018, 9:44 AM

I think I may have just googled the answer to the first bit.

Dolby surround 5.1 has no true .1 channel - it's merely a low pass of of the other tracks. This is what I'm hearing.

DTS has a true LFE channel (I think), but as far asI can see Vegas does not support this.

Looks like I may just have to EQ some of my more bassier actors!

However, I still need to know what format to use to create a 5.1 BluRay.....

Marco. wrote on 7/15/2018, 10:34 AM

Dolby Digital 5.1 AC3 has a "true" LFE channel. It's the player's bass management system which route low frequencies to the subwoofer, it's not the AC3 encoding. You certainly need to uncheck the low frequency cut-off filter setting in the project's audio properties to ensure a "clean" LFE.

Former user wrote on 7/15/2018, 10:36 AM

Yeah, I am not sure where you read that there is no true LFE. Dolby has been the standard 5.1 for several years. Do you have the Dolby Pro in that version of Vegas? It might be the studio version which may not support 5.1 correctly.

Marco. wrote on 7/15/2018, 10:49 AM

Even the non-pro AC3 encoder of Vegas Pro 14 and 15 renders a clean LFE if project properties and render settings are set correctly. I tested with both pure AC3 and AVCHD output.

Former user wrote on 7/15/2018, 11:29 AM

Thanks Marco. I have not use the non-pro so did not know its limitations.

 

Former user wrote on 7/15/2018, 12:42 PM

To create 5.1 surround sound correctly set the audio properties of your project to 5.1 Surround and at render time choose the AC3 Pro 5.1 or WAV PCM 5.1 format that are only supported by the DVD Architect 6.0. If your Vegas 15 does not have the AC3 Pro encoder then use a third party application like Adobe Media Encoder to convert the PCM 5.1 WAV audio created in Vegas or use an older version of vegas that has support for the ac3 Pro format.

Marco. wrote on 7/15/2018, 2:10 PM

While AC3 Pro offers access to all the Dolby Digital 5.1 meta data there should be no need to use the Pro version only to get a correct LFE output. It works fine with the Studio version.

Berty wrote on 7/16/2018, 2:48 AM

Thanks everyone for your help.

So to make sure I've got this right... AC3 Pro 5.1 does encode the LFE channel discretely but it's my decoders that are doing the low pass? If that's the case then I don't have real control over this as it will depend on the viewers decoder. Anyone got any real world tips or best practices? Unless anyone has a better idea I think I will render the project and listen with the bass turned up a bit, that way I can see where my "booming vocals" are and EQ the bass down a bit.

As for burning BluRays... thanks David-tu, using the BluRay template would seem a better idea (I feel a bit thick now!). Thanks - all done.

Marco. wrote on 7/16/2018, 3:34 AM

"AC3 Pro 5.1 does encode the LFE channel discretely"

Both AC3 Pro as well as AC3 Studio does encode the LFE channel discretely.

"it's my decoders that are doing the low pass?"

While it might be the decoder, more likely it is the bass management system. These are different things.

If you want to be sure your LFE channel is encoded correctly you encode a short AC3 test file and offer for download. Then we could try to analyse the channels.

 

Berty wrote on 7/16/2018, 9:43 AM

Thanks Marco. I think I'm getting there. I'm sure that Vegas is encoding correctly. I now have a DVD with surround that works in both my DVD and BluRay systems. As I said I will have to go through the whole film and see where the boomin occurs and just EQ that section a bit.

The BluRay is more problematical. I now have a m2v file created using the BluRay template for the video. This seems to work fine. I am using the same ac3 file I use for the DVD and DVD Architect picks this up when I select my m2v file. It previews fine in DVD Architect. However when I play it I just get a constant screech from all speakers.

Just played the BluRay on my PC and it gives a few screeches then nothing, so it's the BluRay burn that seems to be the fault rather than the players.

Anyone got any idea why the audio is not working ?