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View Full Version : Scenarist AC-3 Encoder - Problem w/ LFE, no output


BassPig
17th April 2007, 04:19
It seems like a straightforward process, one that I have done several times in the past with success, but after having inadvertently deleted some boilerplate content, I am re-constructing that content from scratch again.
The problem I am having this time around is that the 5.1 surround AC-3 track's LFE channel is silent, even though there is content on the input file and LFE is enabled in the Encoder.
Making things more exasperating, is the fact that the LFE channel is audible when using the Audio Playback feature on the AC-3 Encoder, but once the AC3 file is encoded, the LFE is silent, while L,C,R,LS & RS are fine.
I have quadruple-checked the input files, have tried reencoding the output file a dozen or so times with various changes to settings, including changing the bitrate and turning on/off the LFE lowpass filter, etc., all with the same result.
This Encoder has successfully created LFE channels in the past, when I used it to author other 5.1 content.
The affected AC3 file has a property of:
Audio Type AC3
Bit Rate 448kbps
Channel 3:2
LFE On Yes
Bsmod complete main


I also tried encoding with a Bsmod of music & effects, but that did not result in an audible LFE track.

The content in question is a 40 second Dolby Surround setup file, in which I place 5 second pink noise bursts, sequentially, into each channel so the viewer can identify proper speaker hookup/system configuration. All channels but the LFE produce output. The burst that is supposed to come from the LFE channel is not there. Even though I could hear it in the encoder's Audio Playback.

I have been beating around the bush with this vexing little problem for 2 whole days now, and I'm completely stymied. LFE Enable IS checked. It should be as simple as the last three times I successfully encoded LFE channels in 5.1 mixes. This time, the encoder is giving me blank, but enabled LFE tracks and I am at whit's end because I think I must be losing my touch, since I can no longer achieve a simple routine process that I've done before.

It looks like in order to meet schedule demands for this project, I will have to move the encoding process over to another platform and attempt to encode valid Dolby Surround from there, as the AC3 Encoder in Scenarist seems to have become broken, or, more likely, I've been working too many hours and forgot how to use a computer... :(

BassPig
17th April 2007, 05:57
I'm starting to think there might be a problem with my Oppo DV-981HD DVD player's LFE output. I can't get the test signal for the LFE to appear either here, or in the stereo mix.

I did manage to dissect the AC3 file with HeadAC3 and was able to extract a 6-channel wav file, and the last track, sure enough, contained the LFE signal.

But I can't hear it in Scenarist's video player, nor on the standalone Oppo unit.

Most perplexing....


UPDATE: I tried this disc on my wife's Sony DVP-NS71HP and the LFE channel is silent there too.

I have tried two encoders, the one in Vegas, and the one in Scenarist and both yield the same result.

I have checked with the manufacturers of both players and they are indeed correctly configured to play LFE channel audio.

Oddly, the extracted WAV files decoded by HeadAC3 contain audio on the LFE channel.

The mystery deepens.

SealTooGreat
11th May 2007, 21:17
From Sony Vegas 7e Help:
Select the Enable low-pass filter on LFE check box if you want to apply a low-pass filter to each track that is assigned to the LFE channel. Enter a frequency in the Cutoff frequency for low-pass filter box to set the frequency above which audio will be ignored by the LFE channel
Try to uncheck low-pass filter on LFE.