Steve Callas started a similar thread over at AVS. Since I have some issues with AVS
, I decided to start my own thread here. Here's a link to AVS thread: http://www.avsforum.com/avs-vb/showt...8&page=1&pp=30
Mark Seaton on AVS wrote:
When a DD soundtrack is downmixed to stereo or DPL, the LFE channel is thrown away. If you want to listen to DVD soundtracks with a powerful set of stereo main speakers you want to make sure you are in a DD mode and have the system set to yes or no to all of the appropriate speakers. While it should be obvious, if you don't have a center or a sub, be sure that you select that in the setup.
This is correct when strictly talking about downmixing. But almost every receiver/pre/pro has a some kind of bass management, which allows us to redirect the LFE channel into main channels (L&R) if there are only for example two speakers in the system. There are a few receivers that don't handle it perfectly, they usually attenuate the level of the LFE by 6 dB (for example some Marantz units). Disabling either the center or the surrounds when playing DD tracks will cause some problems like loss of dynamics and SPL. Check a few posts down for more information.
This is not the case with DVD players though. There are only a few DVD players which can redirect the LFE channel into main channels (for example Sony DVP-NS900). And of course then the player has to be connected either via digital output (coax/fibre) or via multichannel analog outputs.
If you connect a DVD player via analog stereo outputs (or via SCART to a TV), the LFE channel WILL get thrown away. Dolby specs don't allow LFE to be downmixed into analog stereo outputs.
AC3filter used with Spectrum Labs program does handle the LFE redirection perfectly. Nothing will be left out and no attenuation will be made. Though it requires that the program has correct settings in it. I've been doing these waterfall charts for a while now and I thought I had the correct settings, but today I started explore this matter a little bit more, and found out that the LFE channel level has been +6 dB in all the charts I've done (and in other people's charts too, since most of them were using my settings). Let me explain why.
The AC3filter uses a matrix chart to control the level of individual channels. I've been using the "auto matrix" option all the time, but it doesn't seem to work properly after all. The program correctly downmixes 5.1 channels into 2 channels, but it puts the LFE into both channels (L and R). This shouldn't be done since Spectrum Labs program adds both channels together for a mono signal, which it then monitors. Since the AC3 filter downmixes the LFE into both channels, we get this +6 dB error. But luckily there is an easy solution.
Turn off the "auto matrix". Place a zero in LFE/R cell. LFE/L cell must read 1. Now the LFE channel will be downmixed only to left channel and the relative level compared to redired bass will be correct.
I took some new charts from the WOWT with these new settings, though the results are still pretty much identical with the old ones, since the LFE channel hasn't got much material in it. As you can see, most of the bass is actually redirected bass, not LFE. These charts show the full lightning scene from the first strike to the last one. DTS track was used.