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Old 25th November 2006, 10:05 PM   #1
cujo75 is offline cujo75  United States
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Default Decoding LFE

Sorry if this post is in the wrong place, but it does cover subwoofer input. Wondering if LFE needs to be decoded by a 5.1 receiver or if the info would be avaliable in a 2.1 style set up. I'm considering a 2 chanel for the fronts of course, and a x-over and pro sound amp for my subs. Also, any members in the Huntington/Wayne West Virginia area? There are no audio stores in the area and I would love to hear othe systems.

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Rick
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Old 26th November 2006, 03:09 AM   #2
Volenti is offline Volenti  Australia
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Typically when you down mix to stereo the LFE is mixed into the L+R channels, assuming you don't have a 5.1 receiver and are using the audio out on your DVD this will be performed in the DVD player.

I used a setup similar to this for some time and no problem getting lots of bass from movies.

Though I would think a full setup with a 5.1 receiver would veild better results if only from the greater array of setup options that the receiver would present.
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Old 26th November 2006, 03:32 AM   #3
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When listening to the 2 channel PCM channels the LFE is part of the front channel mix as was stated by the previous post.

However, the LFE channel is recovered only by a low pass filter since it is not a discrete channel. Unless you are downmixing from 5.1 to 2.1 in your HT processor then the LFE will be a discrete channel.

If downmixing from 5.1 to 2.1 then you don't have to have a low pass filter on your subwoofer since it will only contain LFE.
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Old 26th November 2006, 05:02 AM   #4
dangus is offline dangus  Canada
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The processor should only divert the bass to the subwoofer output if the front speakers have been defined as "Small" in the "bass management" setup.

A good receiver will let you adjust this crossover frequency. So, if you had some truly fullrange speakers plus a Contrabass subwoofer, you might set the crossover down at 40 Hz or lower.
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Old 26th November 2006, 08:03 PM   #5
cujo75 is offline cujo75  United States
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thanks a bunch for your help. I want to do a surround pre-amp eventually but they are all so expensive. I have not seen one for less than $1000. Pretty expensive when considering a 5.1 receiver can be had for 400.
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Old 27th November 2006, 09:10 PM   #6
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Quote:
Originally posted by Volenti
Typically when you down mix to stereo the LFE is mixed into the L+R channels, assuming you don't have a 5.1 receiver and are using the audio out on your DVD this will be performed in the DVD player.
Most decoders discard the LFE channel when down-mixing. Given consumer loud speaker capabilities and the channel's 10dB of headroom beyond the screen channels this is the preferred behavior.

This doesn't mean you lose bass - anything that's "important" and not an effect should be recorded in the main channels.
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Old 27th November 2006, 09:13 PM   #7
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Quote:
Originally posted by cujo75
thanks a bunch for your help. I want to do a surround pre-amp eventually but they are all so expensive. I have not seen one for less than $1000. Pretty expensive when considering a 5.1 receiver can be had for 400.
So you use a receiver instead. Many have pre-outs, and a simple voltage divider (1K + 100 Ohms) can be used to get speaker level outputs down to line levels.
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Old 27th November 2006, 09:20 PM   #8
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Another option is a DIY DAC made with the AD1954. This will give you a sub output.
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Old 28th November 2006, 03:20 AM   #9
Pano is offline Pano  United States
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So are we saying that the LFE track contains only LF info? Makes sense, but is there a standard? What's the BW of the LFE track? (He asks reachng for google)
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Old 28th November 2006, 03:33 AM   #10
Pano is offline Pano  United States
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OK. Good article here:
http://www.hometheaterhifi.com/volum...pril-2000.html

I'm supposed to know this stuff, since I used to do Dolby alignments in cinemas. But never did one with an LFE channel. Seems the digital version is limted to 120Hz. In practice rolled off at 80Hz. Plays 10dB louder than the other channels.

So you should be able to tap the LFE output and feed your sub directly. Right?
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