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Old September 9, 2011, 08:28 AM
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Default Is LFE a separate channel? (soundcard troubleshooting)

Just put in a Auzentech X-Meridian into my HTPC and was playing with the setup. I'm using the analog outs to a receiver that is set to 6ch direct - basically it's now just an amp with volume control. For speakers I essentially have a 4.1 setup, as in mains, surrounds, and a sub - no center channel speaker.

When I set the sound card to "4 speakers" and play a BD I get what I expect, surround with full bass to each speaker. When I set the soundcard to "6 Speakers" I get the same output. I would have expected to lose most or all dialog since that should now be sent to a CC that isn't there and I would expect to get something out of the subs but this doesn't happen either.

So I guess just part of my troubleshooting I need to know if the LFE is indeed a separate recorded channel that exists in the sound track or is it derived from the L/R front channels or a sum of all 5 channels?
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Old September 9, 2011, 08:55 AM
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Copied from Wikipedia Re: LFE

Quote:
The bass management in surround sound replay systems is that bass content in the incoming signal, irrespective of channel, should be directed only to loudspeakers capable of handling it
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Old September 9, 2011, 09:04 AM
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Quote:
Originally Posted by biff View Post
Just put in a Auzentech X-Meridian into my HTPC and was playing with the setup. I'm using the analog outs to a receiver that is set to 6ch direct - basically it's now just an amp with volume control. For speakers I essentially have a 4.1 setup, as in mains, surrounds, and a sub - no center channel speaker.

When I set the sound card to "4 speakers" and play a BD I get what I expect, surround with full bass to each speaker. When I set the soundcard to "6 Speakers" I get the same output. I would have expected to lose most or all dialog since that should now be sent to a CC that isn't there and I would expect to get something out of the subs but this doesn't happen either.

So I guess just part of my troubleshooting I need to know if the LFE is indeed a separate recorded channel that exists in the sound track or is it derived from the L/R front channels or a sum of all 5 channels?
LFE is a separate channel and a lot of receivers or subwoofers have a specific spot to hook up the cables for this.
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Old September 9, 2011, 12:41 PM
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Quote:
Originally Posted by Jackquelegs View Post
Copied from Wikipedia Re: LFE
... shoulda checked wiki ... however the portion of the quote you copied doesn't really answer the question, it just says don't send bass to speakers that can't handle it. The next sentence sounds like it says that the 'bass management system' will/can strip the bass content from any/all channels and add it to the LFE channel information to make the 'Subwoofer' out. Apparently the LFE channel itself contains content from 3 to 120Hz.

So I guess now to figure out why the soundcard isn't passing along the LFE channel to the amp.
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Old September 9, 2011, 02:03 PM
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Sorry I thought it was sufficient. Just says LFE is not a channel based sound enhancement, more like add XXdB of bass to whatever it's hooked up to
Yeah I only thought to answer the LFE = channel dependance question...

Good luck with your setup, but I have a feeling it's not LFE that's causing this
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Old September 9, 2011, 08:05 PM
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Originally Posted by Jackquelegs View Post
Sorry I thought it was sufficient. Just says LFE is not a channel based sound enhancement, more like add XXdB of bass to whatever it's hooked up to
Haha, OK I get it. I should've done my own my own homework before taking the easy way out and asking here first. So I'm not denying I should be made fun of. Shoulda seen it coming with that first quote - you had me brewing on it all day on some random quote that had nothing to do with what I was asking.

Just going to clear it up as someone else might read this and be thrown for a loop, then you can continue messing with me.

The LFE channel is exactly a channel (according to the wiki and other sources I've read) designed to enhance or supplement (i'm going to consider those synonyms for this discussion) the bass content content of the other channels. It is not a channel where bass content is just added and sent out to 'what ever it's hooked up to'. The bass management system, be it receiver or otherwise creates a "subwoofer out" signal by adding the LFE channel + the content selected from the other channels. For example if you set the other speakers to small and set the XO frequency at 100Hz the "subwoofer out" will add the LFE channel content plus the sub 100Hz content from the selected channels.


Quote:
Originally Posted by Jackquelegs View Post
Good luck with your setup, but I have a feeling it's not LFE that's causing this
There was your give-a-way because the LFE is the exact problem! And that's what I'm enquiring about.

In all honesty, thanks! It made me do my own research to find out what's what, which I fully admit I should have done in the first place. I'll know better next time. So continue flogging...

Though I still have to find out why the sound card is not passing along the LFE channel....
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Old September 13, 2011, 02:02 PM
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It looks like you're using analogue out from your soundcard to your receiver.

You have 4 channels + a dedicated sub connected to your receiver.

I assume you're using stereo mini jack to RCA Y-cables for the front output from your soundcard to the front input on your receiver. Ditto for the surround channels. If you want the LFE to work you have to do the same with the C/LFE output on your soundcard and connect to the Centre/LFE input on your receiver. Set your soundcard's out put to 4.1 and you should be able to utilize the proper LFE channel for Blu-Rays/AC3/DTS etc.

You should still hear the centre track just fine in 4.1 mode, in fact some audiophiles actually prefer this as it's hard to sometimes get a high enough quality centre channel speaker to match expensive front channel speakers.

--

Er I just realized the above might be useless info to you. Anyway, the LFE track is only used in audio tracks encoded in AC3/DTS etc formats.

When listening to music the subwoofer kicks in and fills in the lower frequency sounds that are at or below your crossover frequency as set in your AVR (probably ideal to set this in your soundcard settings as well).
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Old September 13, 2011, 09:15 PM
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Yes I'm using the analog outs from the soundcard connected to the reciever with the mini jack to RCA y cables including one for the CC/LFE. The receiver is set to 6ch direct in, so it's basically just an amp with no signal processing with the exception of volume.

In the driver window I have a choice of 4ch/6ch/8ch. When I select 6ch the little pictures representing the sub and CC appear. Clicking on a speaker icon sends a test signal to the associated speaker and the signal does go through to the sub so it appears everything downstream of the soundcard is setup as it should be. I haven't had a chance to look into this since but I don't recall seeing an option for a virtual CC, though the card seems to be doing it anyway since there doesn't seem to be anything missing (like dialog). My last setup used digital coax to the receiver and a couple times when I accidentally enabled the CC you could hear all the surrounding noise but zero dialog - unless it was coming from off screen. So the soundcard seem to be 'stuck' in 4ch mode regardless of where I set it on the processing side of things.

I don't want the sub kicking in for music, but thankfully it doesn't now anyway. In the last setup the receiver would automatically up mix 2ch audio to 5.1 which was very annoying. As for XO frequencies, well I don't really want to use any at the momment until I do a little more testing at least. I don't ever get a chance to crank it so my mains and surrounds can handle the low frequency content at my levels. Once I get the LFE channel passing through to the sub amp I may then decide to add in the low frequency content from the from the other channels... just because my mains can handle a 20Hz signal doesn't mean they can produce it.

But that brings up some questions. I wonder if the XO frequency set in the "bass handling section" of the driver screen affects the LFE channel as well, or just the remaining 5ch.? For example of I set it to 50Hz will the sub out of the sound card consist of the LFE channel (3Hz to 120Hz) + the 50Hz and down content of the remaining 5 ch. or will it lowpass the LFE channel as well at 50Hz.?

I'm not really very familiar with the different encoding standards so I'm not sure what standard is used on blurays. I suppose I should look into that to even see if a LFE channel is present in the first place to be passed to the sub amp. FWIW I did try setting up the bass management to divert some bass away from the mains and send it to the sub and still I got no output from the sub though TBH I can't say it sounded like it highpassed the signal going to the mains either. I'll have to do some playing when I get some time.
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