LFE, subwoofers and interconnects explained - Page 25 - AVS Forum
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post #721 of 777 Old 08-13-2010, 11:00 PM
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Originally Posted by wse View Post

Roger did you have any one calibrate your SSP-800?

Nope. DIY with XTZ, REW, BassQ, ears, patience, and a Rane GEQ patched in for "spectral training and detection."
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post #722 of 777 Old 08-28-2010, 03:25 PM
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I don't think this has been mentioned in the thread, so I thought I'd bring it up...

In regards to using an HTPC, how is the LFE handled there?

After testing for a little while I confirmed that my receiver (Sony STR-DA7100ES) does have the LFE channel 10dB down on LPCM over HDMI. There is no way to adjust this unfortunately. Sony remembered about it on the multi-analog inputs (there is a +10dB option for those) but somehow forgot about it for HDMI. Given it's an HDMI 1.0 receiver I guess it's forgiveable... (Since it's a first gen-HDMI AVR all I can do over HDMI is bitstream of lossy formats and PCM, bitstream of HD formats is not an option.)

Anyway the fact that I playback BD/HD-DVD from an HTPC got me thinking of a proper workaround In the soundcard driver's "Room Correction" settings you can boost individual channels. So, I boosted the subwoofer* level by the maximum which happened to be +10dB. The "soundcard" happens to be the HDMI output of an ATi videocard, which is supported in software via a Realtek driver.

*The subwoofer level adjustment should = LFE provided the speakers are set to full-range and thus bass-management disabled (should be the equivalent to setting LARGE on an AVR). The AVR still does bass management so I don't need the PC to do this job for me.

So I think I "fixed" the problem. Comparing switching from bitstreamed DD and decoded-to-multi-PCM output of the same track it sounds quite close. However it doesn't sound exactly the same, I *think* it is still down a little bit. Eventhough the driver is setup for full-range (i.e. "large") speakers, is it possible the PC is outputting the LFE by -15dB instead of -10dB?
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post #723 of 777 Old 08-28-2010, 03:53 PM
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Originally Posted by ES_Revenge View Post

After testing for a little while I confirmed that my receiver (Sony STR-DA7100ES) does have the LFE channel 10dB down on LPCM over HDMI. There is no way to adjust this unfortunately. Sony remembered about it on the multi-analog inputs (there is a +10dB option for those) but somehow forgot about it for HDMI.

They didn't forget. It's the only way that LFE can be handled in digital so that it does not cause overload. The -10 dB LFE signal can still reach 0 dBFS--max PCM level.

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The AVR still does bass management so I don't need the PC to do this job for me.

How are you connecting the sound card into the AVR? If analog, how can it do bass management? If digital, the LFE should remain as -10 dB so that the AVR can handle it correctly.
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post #724 of 777 Old 08-28-2010, 04:04 PM
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Quote:
Originally Posted by Roger Dressler View Post

They didn't forget. It's the only way that LFE can be handled in digital so that it does not cause overload. The -10 dB LFE signal can still reach 0 dBFS--max PCM level.

I appreciate the reply Roger

By forgot I meant the AVR lacks a facility to boost the incoming LFE of an LPCM signal (over HDMI) by the required 10dB. When i say they remembered it on the analog, I meant that in reference to the fact that the multi-ch analog inputs do have this option.

To summarise:
Multi-Ch Analog: Adjustment for 0 or +10dB boost for LFE.
Multi-PCM Digital (over HDMI): No adjustment, the signal comes in 10dB low (as it's supposed to) but does not get boosted prior to output (as it should).

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Originally Posted by Roger Dressler View Post

How are you connecting the sound card into the AVR? If analog, how can it do bass management? If digital, the LFE should remain as -10 dB so that the AVR can handle it correctly.

There really isn't a soundcard, as I tried to say. The "soundcard" is the HDMI output of the ATi videocard.

You are correct that the signal should be 10dB down over HDMI but the receiver does not boost it, so I figure I have to boost it somewhere to fix the deficiency. This seems like the most proper way to do it because it doesn't end up overboosting redirected bass. I don't hear any clipping of the signal (in the digital domain a hard clip should be heard as a click, correct?) so I think it's okay this way.

As an aside, because this receiver is a Digital Drive receiver it can actually bass manage the multi-analog inputs But that's besides the point here as I'm using HDMI.
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post #725 of 777 Old 08-28-2010, 04:53 PM
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So I kept reading some more wondering why I wasn't getting digital-domain clipping and I think it's because the driver prevents the output from clipping? Or are digital-domain clips just outright lost information?

If you look at the level meter in Windows, you can see when you hit the peak output. While it works for all channels at the same time, if you test only one channel however, you will see the output level for just that channel.

Now using the channel test (a short musical blurb, if you will) you can see the level meter flash and hit the peak when the music note hits the peak. But if you boost the channel level in "room correction" you just see the bar go "more solid". I tried it for one of the main channels because I figured clipping would be more audible there and though it sounded overall louder, the peak I don't think it's any louder, hence the no clipping.

So anything that is 0dB stays there, something that is -10db will be 0dB and something that is -5dB just goes to 0dB as well. So really, I'm thinking, all I'm doing here is compressing the dynamic range! LOL. This is in contrast to the analog outputs which will distort using the same test (which is stupid because the line voltage is still low but that's another story altogether).

In this case I'm compressing the sub channel by dialing it up to "+10dB". I haven't really fixed anything at all, lol. According to what I've read an LFE signal that is 105dB, should be reproduced as 115dB, but I'm still getting 105dB. So this explains why the output still didn't sound "quite right", I've just compressed the sub channel so that sounds that are 10dB below the 0dBfs level are boosted by 10dB and anything above that is just boosted to 0dB.

Roger, if it wasn't for this explanation:
Quote:
Originally Posted by Roger Dressler View Post

The -10 dB LFE signal can still reach 0 dBFS--max PCM level.

I would not have come to this conclusion on my own, lol.

So while I haven't fixed anything I guess compressing the dynamic range of the LFE channel is about all I can do to make it better. I could set all my speakers to LARGE in the AVR, forego any bass management and then set the sub level to +10dB, but I'd have to remember to lower the sub for every other source (and raise it for watching BD/HD-DVDs). Man this 10dB LFE bug really sucks!

I think I'm just going to stay with my ghetto fix of compressing the sub channel as it at least sounds better if not proper
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post #726 of 777 Old 08-28-2010, 05:23 PM
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Quote:
Originally Posted by ES_Revenge View Post

To summarise:
Multi-Ch Analog: Adjustment for 0 or +10dB boost for LFE.
Multi-PCM Digital (over HDMI): No adjustment, the signal comes in 10dB low (as it's supposed to) but does not get boosted prior to output (as it should).

I see, I guess it's one of the AVRs that messed up on that. There were a few such units back in the day.

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You are correct that the signal should be 10dB down over HDMI but the receiver does not boost it, so I figure I have to boost it somewhere to fix the deficiency. This seems like the most proper way to do it because it doesn't end up overboosting redirected bass. I don't hear any clipping of the signal (in the digital domain a hard clip should be heard as a click, correct?) so I think it's okay this way.

If it clips, it will be filtered by the LPF in the bass management, and by the subwoofer itself. Might not hear the usual nastiness. It might just limit the loudest LFE peaks.

Can you split the difference--attenuate the main channels 5 dB and raise the LFE 5 dB? Might be a safer compromise.
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post #727 of 777 Old 08-29-2010, 01:15 PM
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Originally Posted by ES_Revenge View Post

By forgot I meant the AVR lacks a facility to boost the incoming LFE of an LPCM signal (over HDMI) by the required 10dB. When i say they remembered it on the analog, I meant that in reference to the fact that the multi-ch analog inputs do have this option.

Processors almost never have a user option to boost LFE with digital. The boost should be done by the software for both encoded bitstream soundtracks and for PCM. The user option for the boost is there for analog because the software doesn't do the boost on its own.

Quote:
To summarise:
Multi-Ch Analog: Adjustment for 0 or +10dB boost for LFE.
Multi-PCM Digital (over HDMI): No adjustment, the signal comes in 10dB low (as it's supposed to) but does not get boosted prior to output (as it should).

How do know your AVR is not doing the boost correctly with PCM?
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post #728 of 777 Old 08-30-2010, 07:06 AM
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Quote:
Originally Posted by Roger Dressler View Post

I see, I guess it's one of the AVRs that messed up on that. There were a few such units back in the day.

Yeah sucks, unfortunately

Quote:
Originally Posted by Roger Dressler View Post

If it clips, it will be filtered by the LPF in the bass management, and by the subwoofer itself. Might not hear the usual nastiness. It might just limit the loudest LFE peaks.

Yeah definitely no clipping but the highest it gets is 0dB (which is why I said above I wouldn't have realised this properly unless you metioned that the sub signal still hits 0dBfs in the digital domain and the boost has to come after this--then it was like a light went on over my head, lol.)

Turns out all I'm effectively doing is compressing the DR on the sub channel by making everything lower than -10dB (signal wise) boosted by 10dB, and then anything between there and 0dB just goes to 0dB. And if it's already at 0dB it's not getting any higher obviously.

Quote:
Originally Posted by Roger Dressler View Post

Can you split the difference--attenuate the main channels 5 dB and raise the LFE 5 dB? Might be a safer compromise.

Well I guess the exactly correct solution would be to set all the other channels to -10dB and then compensate by having the master volume on the receiver up 10dB. The irony of this is that this is almost the exact problem I was trying to get away from with the multi-channel analog output from the PC (ALC889). See, analog outputs from a PC are not at the line level of consumer electronics gear, they are quite a bit below--probably 10-15dB lower in fact--meaning the volume has to be cranked up on the receiver for the same level you get from any CE gear's analog output.

My previous receiver didn't have HDMI, so I was using the analog only but was sick of the low-line level issue. Of course I also now have a BDP-S550 with multi-analog output (which has proper line level) but that was really bought for another room. If it wasn't for how much I like the Digital Drive/S-Master Pro amp section, I'd probably re-sell the receiver and get a newer one that has the proper adjustment for the LFE channel.

Oh well, I think I'm just going to live with my handiwork of compressing the sub channel.

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Originally Posted by BIslander View Post

Processors almost never have a user option to boost LFE with digital.

I dunno that's not what I'm reading in this thread. The very reason the thread exists is because there's receivers that have issues with this, no?

All the newer Sony receivers after the DAx100ES line (i.e. DA3200ES and higher and later) have an option for HDMI PCM LFE--"0dB", "+10dB", or "AUTO". (How auto works I'm not sure but yeah it is an option.)

Quote:
Originally Posted by BIslander View Post

The boost should be done by the software for both encoded bitstream soundtracks and for PCM.

Yes I understand that. But for PCM this doesn't happen on some receivers (again as this thread points out).

Quote:
Originally Posted by BIslander View Post

How do know your AVR is not doing the boost correctly with PCM?

Well if I test a DTS-HD (MA) track using the core (so I can bitstream it), the LFE is way more pronouced in bitstreaming it compared to decoding it and sending it as PCM. Same can be replicated going from bitstreaming a DD track to the DTS-HD decoded and sent as PCM. However to rule out any differences in the mix/track, I made certain using the DTS core which conveniently allows for this.

At first I didn't think it was wrong but after testing a few tracks I realised the LFE was quite low in comparison and the receiver definitely has the LFE bug with PCM over HDMI.
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post #729 of 777 Old 08-31-2010, 07:39 AM
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Originally Posted by ES_Revenge View Post

I dunno that's not what I'm reading in this thread. The very reason the thread exists is because there's receivers that have issues with this, no?

That's one issue discussed in this thread. There's more discussion of analog processing. But, yes, some older receivers failed to properly boost LFE. I don't recall seeing that issue come up with any newer models. But, of course, it's certainly possible the 7100ES has the bug. Unfortunately, there's no owner thread for that AVR. But, I don't see any posts from owners complaining about LFE issues.

Quote:


All the newer Sony receivers after the DAx100ES line (i.e. DA3200ES and higher and later) have an option for HDMI PCM LFE--"0dB", "+10dB", or "AUTO". (How auto works I'm not sure but yeah it is an option.)

Which is why I said receiver almost never have such settings. What does the manual say about that setting?


Quote:


Well if I test a DTS-HD (MA) track using the core (so I can bitstream it), the LFE is way more pronouced in bitstreaming it compared to decoding it and sending it as PCM. Same can be replicated going from bitstreaming a DD track to the DTS-HD decoded and sent as PCM. However to rule out any differences in the mix/track, I made certain using the DTS core which conveniently allows for this.

At first I didn't think it was wrong but after testing a few tracks I realised the LFE was quite low in comparison and the receiver definitely has the LFE bug with PCM over HDMI.

I'd test with a calibration disc rather than movie soundtracks. Set speakers to large in your receiver. Play the tones via bitstream and write down the levels on an SPL meter for all channels. Then play them again for output as PCM. If the LFE output is -10dB compared to the expected output, then the AVR isn't boosting LFE properly.
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post #730 of 777 Old 09-01-2010, 12:41 AM
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Quote:
Originally Posted by BIslander View Post

That's one issue discussed in this thread. There's more discussion of analog processing. But, yes, some older receivers failed to properly boost LFE. I don't recall seeing that issue come up with any newer models. But, of course, it's certainly possible the 7100ES has the bug. Unfortunately, there's no owner thread for that AVR. But, I don't see any posts from owners complaining about LFE issues.

Yeah I know what you mean. I tried to find info before I bought it but there wasn't much out there so I just took a chance. I think no one complains about it because it's tough to tell at first. You think it's alright at first (and I did too) but if you really start to listen carefully (and actually feel for the bass/lfe) it's quite apparent.

The closest thing I came to was the thread at AVforum (UK) that mentioned "possible LFE issue" regarding PCM over HDMI, but nothing concrete.

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Originally Posted by BIslander View Post

Which is why I said receiver almost never have such settings. What does the manual say about that setting?

There is no setting, thus it says nothing. (The ones that do have it explain it I'm sure.) The 7100ES was released in like 2006, the HDMI is literally 1.0. Officially it doesn't even support 1080p (it's not in the EDID map) though 1080p works fine through it provided you have a device that can "force" 1080p. The documentation on the HDMI audio is pretty vague. It doesn't even really mention any specifics nevermind anything about LPCM over HDMI. Also it doesn't mention that despite it technically being a 7.1-capable receiver (with proprietary 9.1 expansion), LPCM through HDMI is limited to 5.1 channels.


Quote:
Originally Posted by BIslander View Post

I'd test with a calibration disc rather than movie soundtracks. Set speakers to large in your receiver. Play the tones via bitstream and write down the levels on an SPL meter for all channels. Then play them again for output as PCM. If the LFE output is -10dB compared to the expected output, then the AVR isn't boosting LFE properly.

You're right, that is the scientifically correct way of confirming it, however I don't have that equipment available. But I can tell nonetheless, trust me. When my floor is shaking at a certain passage when bitstreaming a DTS core from an HD MA track, and you can barely hear the sub (never mind any real vibration through the floor) when the DTS-HD is decoded and played through HDMI, it's not hard to tell. I'm quite sure it's 10dB down, at least.
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post #731 of 777 Old 09-01-2010, 06:58 AM
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Originally Posted by ES_Revenge View Post

There is no setting, thus it says nothing. (The ones that do have it explain it I'm sure.)

I was asking about one of these that you'd mentioned previously: "All the newer Sony receivers after the DAx100ES line (i.e. DA3200ES and higher and later) have an option for HDMI PCM LFE--"0dB", "+10dB", or "AUTO". (How auto works I'm not sure but yeah it is an option.)"

I looked at the STR-DA3200ES manual, btw, and didn't see a PCM SW boost setting. It allows you to trim subwoofer levels, the same as the other speakers, but the only boost setting is for analog.

Given the lack of information available elsewhere, a call to Sony support may be in order. Meanwhile, you seem to have found an acceptable workaround.
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post #732 of 777 Old 09-09-2010, 08:27 AM
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Quote:
Originally Posted by BIslander View Post

I was asking about one of these that you'd mentioned previously: "All the newer Sony receivers after the DAx100ES line (i.e. DA3200ES and higher and later) have an option for HDMI PCM LFE--"0dB", "+10dB", or "AUTO". (How auto works I'm not sure but yeah it is an option.)"

I looked at the STR-DA3200ES manual, btw, and didn't see a PCM SW boost setting. It allows you to trim subwoofer levels, the same as the other speakers, but the only boost setting is for analog.

Ah I see. Yes it seems I was mistaken, it's the DAx300ES where this option was added. Whether or not the DAx200ES receivers get this right I'm not sure now.

To save you from downloading another manual, from the DA3300ES manual it explains the option as:

Quote:
Originally Posted by STR-DA3300ES Manual View Post

HDMI SW Level
Lets you set the level of the sub woofer to 0 dB or +10 dB when PCM signals are input via an HDMI connection. You can set the level for each HDMI input independently.
-0 dB

-AUTO
-*Automatically sets the level to 0 dB or +10 dB depending on the frequency.

-+10 dB

Whatever it means by "depending on the frequency" I have no idea but that's what it says.

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Originally Posted by BIslander View Post

Given the lack of information available elsewhere, a call to Sony support may be in order. Meanwhile, you seem to have found an acceptable workaround.

Yeah only Sony is one of those companies where the "support" you get is just generic lines pre-written on the pages of the tech support manual. I'm pretty sure they'd just be clueless. Even if I could get as far as some engineering department they'd probably just give an answer like it being an unfortunate design problem that isn't correctable.
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post #733 of 777 Old 09-14-2010, 08:25 PM
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i am about to buy an oppo 83se. i will run it through my classe ssp 60 pre-pro into a 5 channel theta dreadnought II. i am using a pair of dynaudio consequence speakers as my mains. they are large speakers with a great bass response. i have never felt the need for a subwoofer in listening to music. for example, the eric clapton "one more night" dvd sounds spectacular through my system (currently sony ns999es dvd player). i emailed oppo to ask if i can turn off the subwoofer output in order to send all the bass to my mains, and they answered yes, i can set subwoofer to off, but i will lose all lfe information.

if my speakers have good bass extension, will i notice the loss of the lfe extension (explosions and earthquakes in movies are really not that important to me)?

or will a failure to filter out the lfe info and send it to a subwoofer overload my main channels?

i love my system's bass response, and i don't really want to spend $2000 or more to get a subwoofer that matches my mains in quality unless i really have to.

thanks
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post #734 of 777 Old 09-14-2010, 11:43 PM
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Quote:
Originally Posted by johnsmolowe View Post

if my speakers have good bass extension, will i notice the loss of the lfe extension (explosions and earthquakes in movies are really not that important to me)?

Only you can decide that, my son.

Quote:


or will a failure to filter out the lfe info and send it to a subwoofer overload my main channels?

The bass in the main channels of movies is no more potent than that of certain CDs. No worries.

Quote:


i love my system's bass response, and i don't really want to spend $2000 or more to get a subwoofer that matches my mains in quality unless i really have to.

No need. Try it without the LFE and see how she goes. I assume that your center and surrounds are less bass-capable than the main L/R, so tell the BD player to do the bass management -- C/Ls/Rs = small. That way important bass will not go missing.

And if you still feel like you want to get a taste of LFE, the attached shows a simple way to get there with a handful of resistors. The insertion loss is 6 dB, so the C/Ls/Rs get trimmed down 6dB in the player to match. While this will feed some LFE to the mains, it's still about 5 dB lower than "calibrated" so it will not overly stress them.
LL
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post #735 of 777 Old 09-15-2010, 07:11 AM
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Quote:
Originally Posted by johnsmolowe View Post

i am about to buy an oppo 83se. i will run it through my classe ssp 60 pre-pro into a 5 channel theta dreadnought II. i am using a pair of dynaudio consequence speakers as my mains. they are large speakers with a great bass response. i have never felt the need for a subwoofer in listening to music. for example, the eric clapton "one more night" dvd sounds spectacular through my system (currently sony ns999es dvd player). i emailed oppo to ask if i can turn off the subwoofer output in order to send all the bass to my mains, and they answered yes, i can set subwoofer to off, but i will lose all lfe information.

if my speakers have good bass extension, will i notice the loss of the lfe extension (explosions and earthquakes in movies are really not that important to me)?

or will a failure to filter out the lfe info and send it to a subwoofer overload my main channels?


i love my system's bass response, and i don't really want to spend $2000 or more to get a subwoofer that matches my mains in quality unless i really have to.

thanks



I faced your problem in the late '90's. I have VMPS STIII speakers at LF and LR. These are 7 ft high speaker with an array of speakers that extend low frequency to 17Hz -3dB. As Dolby Digital became more popular, I wanted I wanted to hear the information from the LFE channel. My pioneer preamp did not have a mode where I could send the information to the LF and RF. I bought a Velodyne F1800II. It was the best thing I ever did. Try it, you will enjoy it.

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post #736 of 777 Old 09-15-2010, 05:25 PM
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More on the resistor "Wye" circuit.

http://www.rane.com/note109.html

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So, I'm a total noob at the sub thing, and I'm trying to configure my system. I'm running analogue multichannel outs from my Panny DMB-BD55 to my Krell Showcase pre/pro. Obviously, I'm going to need to dial up the sub level in the Krell, but how do I know whether to make the increase 10db or 15db? And does anyone know if the Panny properly applies the 10db increase to the redirected bass when it does bass management?

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post #738 of 777 Old 09-15-2010, 08:10 PM
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So, I'm a total noob at the sub thing, and I'm trying to configure my system. I'm running analogue multichannel outs from my Panny DMB-BD55 to my Krell Showcase pre/pro. Obviously, I'm going to need to dial up the sub level in the Krell, but how do I know whether to make the increase 10db or 15db? And does anyone know if the Panny properly applies the 10db increase to the redirected bass when it does bass management?

With bass manahgement in the BD55, the sub output should be -15dB. But, an SPL meter will tell you what you need to know.

Redirected bass should not be boosted by the player. It should be lowered by 15dB and LFE dropped by an extra 5dB to make room for the directed bass. The combined SW output (LFE + redirected bass) should arrive at the processor in need of a 15dB boost relative to the main channels.
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post #739 of 777 Old 09-15-2010, 08:27 PM
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Originally Posted by BIslander View Post

With bass manahgement in the BD55, the sub output should be -15dB. But, an SPL meter will tell you what you need to know.

Redirected bass should not be boosted by the player. It should be lowered by 15dB and LFE dropped by an extra 5dB to make room for the directed bass. The combined SW output (LFE + redirected bass) should arrive at the processor in need of a 15dB boost relative to the main channels.

Perfect, thanks. I've got an SPL meter but have never used it; I'll essentially be using it to make sure that I'm getting the same level from every speaker, including the sub? I'm just a bit confused about the whole calibration-with-meter process - all this talk of flat responses and such.

One thing I'm confused about is the focus on the boost to the sub in the receiver or processor; since the sub has a volume knob, why don't you just ignore the boost in the processor and just set the volume knob at whatever level gives you the same output as the other speakers?

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post #740 of 777 Old 09-15-2010, 08:37 PM
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Originally Posted by Speedskater View Post

More on the resistor "Wye" circuit.

http://www.rane.com/note109.html

Just curious, as you didn't mention anything in your post. What is this in reference to? I am of course aware of my recent post showing bass mixing using resistors, but the Rane paper is about tapping 2 channels to feed a subwoofer, and OP johnsmolowe has no subwoofer--which is the crux of the problem.
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post #741 of 777 Old 09-15-2010, 09:59 PM
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Originally Posted by win200 View Post

Perfect, thanks. I've got an SPL meter but have never used it; I'll essentially be using it to make sure that I'm getting the same level from every speaker, including the sub? I'm just a bit confused about the whole calibration-with-meter process - all this talk of flat responses and such.

Yes. When you play the tones on a calibration disc, you want to set all speakers, including the sub, to the same SPL level. The tones on the disc account for the extra 10dB output of LFE, meaning you can use the same level for all channels when calibrating.

Quote:


One thing I'm confused about is the focus on the boost to the sub in the receiver or processor; since the sub has a volume knob, why don't you just ignore the boost in the processor and just set the volume knob at whatever level gives you the same output as the other speakers?

That's fine, as long as you are only calibrating for analog. But, if you also plan to play digital sources, cranking up the volume of sub will mean too much bass for digital. So, you then have to go into the receiver and lower the digital SW output by the amount you turned up the volume on the sub. Calibrating a system for just analog or digital is pretty straightforward. It gets more difficult when you want to be able to play both types of audio without needing to make manual adjustments when switching types.

This can get a little confusing (a lot confusing?). But here's the deal:

By convention, LFE is recorded low to prevent clipping during transmission and has to be boosted somewhere downstream. That's true with both digital and analog transmission. The output from the player always has LFE 10dB lower than it's supposed to be.

With digital, the receiver software handles the boost automatrically prior to the digital-analog conversion. That means the sub output is already where it should be before arriving at the SW. Turning up the volume on the sub would do the boost a second time, creating too much bass.
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post #742 of 777 Old 09-16-2010, 12:41 AM
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Hi Win,

It is with some trepidation that wade into your exchange with BIslander, as his abundant knowledge of these matters is unrivaled. I'd just like to add some additional color.

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Originally Posted by BIslander View Post

Yes. When you play the tones on a calibration disc, you want to set all speakers, including the sub, to the same SPL level. The tones on the disc account for the extra 10dB output of LFE, meaning you can use the same level for all channels when calibrating.

Where the fly meets the ointment is that all sorts of things affect how those LFE test tones will read on an SPL meter. The choice of noise spectrum, the response in your room, and the meter itself. All this adds up to a lot of tolerance--like +/- 5 dB or more.

Yet, even with all that, the test noise and the SPL meter can yield excellent matching of the analog input to the digital input. The basis for the whole exercise is to assume that you have your Krell's bass management and speaker trims all set up exactly as you like for digital sources. If you are happy there, then the mission is simply to get the analog path to act the same. To do so:

1) Set the player's bass management the same as the Krell, as much as possible. Small/large, frequency, time delays.

2) Play the test tone disc. (I find the THX Optimizer tones work well). Using the digital input, note the SPL levels on the meter. This is the target

3) Now switch to the analog input and play the same tones. You may have to shift the master volume to normalize the levels of, say, the Left channel. After that, don't move the MV again. Then check all 5.1 channels and compare them to the first readings. Any differences in level have to be made up somewhere, either in the Krell (hopefully it offers dedicated analog bypass gain trims for each channel), or if not, in the BD player. If you run into difficulties calibrating the sub, there's a way around it.

Once they match, you are done.

Quote:
Originally Posted by BIslander View Post

By convention, LFE is recorded low to prevent clipping during transmission and has to be boosted somewhere downstream. That's true with both digital and analog transmission. The output from the player always has LFE 10dB lower than it's supposed to be.

With digital, the receiver software handles the boost automatrically prior to the digital-analog conversion. That means the sub output is already where it should be before arriving at the SW. Turning up the volume on the sub would do the boost a second time, creating too much bass.

If I may clarify. Yes, in one sense the LFE boost is done in the DSP. When the LFE comes into the bass manager, it is only attenuated 5 dB whereas the redirected bass from the other channels is attenuated 15 dB. Then they are summed together to create the sub signal. The LFE is thus restored to its +10 dB advantage over the other channels. However, that composite sub signal is still 15 dB low as it hits the DAC. It is up to the analog stages to apply whatever gain is needed into the subwoofer amp (which also has its own gain control) to reach the calibrated level.
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post #743 of 777 Old 09-16-2010, 07:07 AM
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Roger & BIslander,

Thank you both for the feedback. I've put off doing this for years, literally; I love audio and HT, but I don't enjoy the tweaking and technical aspects.

Just a couple of remaining questions:

When it's time to play the test tones, what volume do I set the Krell to? It seems that if I set the volume too low, I won't be able to get the test tones to register 75 or 85db when they're played.

Also, it's my understanding that certain tones are designed to be used to calibrate to certain decibel levels - is that correct? And am I also correct in assuming that I'd have to use a different (lower) tone for the sub?

Thanks so much, guys - I can't help but feel obnoxious asking all these question.

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post #744 of 777 Old 09-16-2010, 08:43 AM
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Quote:
Originally Posted by Roger Dressler View Post

If I may clarify. Yes, in one sense the LFE boost is done in the DSP. When the LFE comes into the bass manager, it is only attenuated 5 dB whereas the redirected bass from the other channels is attenuated 15 dB. Then they are summed together to create the sub signal. The LFE is thus restored to its +10 dB advantage over the other channels. However, that composite sub signal is still 15 dB low as it hits the DAC. It is up to the analog stages to apply whatever gain is needed into the subwoofer amp (which also has its own gain control) to reach the calibrated level.

Thanks for that clarification. I did not realize that the gain was being applied after the DAC, although that makes sense.


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Originally Posted by win200 View Post

When it's time to play the test tones, what volume do I set the Krell to? It seems that if I set the volume too low, I won't be able to get the test tones to register 75 or 85db when they're played.

Set it at the reference point for your system - 0 dB if your master volume uses that kind of scale.

Quote:


Also, it's my understanding that certain tones are designed to be used to calibrate to certain decibel levels - is that correct?

Theaters calibrate to 85dB, which is very loud. I think home calibration discs are generally designed for 75dB.

Quote:


And am I also correct in assuming that I'd have to use a different (lower) tone for the sub?

Not sure what you mean here. Calibration discs control the frequencies and levels of the tones.

Quote:


Thanks so much, guys - I can't help but feel obnoxious asking all these question.

Not at all. I often learn new stuff in these discussions.
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post #745 of 777 Old 09-16-2010, 10:37 AM
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Originally Posted by win200 View Post

Also, it's my understanding that certain tones are designed to be used to calibrate to certain decibel levels - is that correct? And am I also correct in assuming that I'd have to use a different (lower) tone for the sub?

The tones from the Krell are presumably intended to be 75 dB. The manual should say.

Most test discs record their cal test signals at -30 dBFS, which would play at 75 dB. The oddball exception to that is the AIX demo disc that comes with Oppo players. Those tones are recorded at -20 dBFS, so they would play at 85 dB.
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post #746 of 777 Old 09-16-2010, 11:18 AM
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Originally Posted by Roger Dressler View Post

The tones from the Krell are presumably intended to be 75 dB. The manual should say.

Most test discs record their cal test signals at -30 dBFS, which would play at 75 dB. The oddball exception to that is the AIX demo disc that comes with Oppo players. Those tones are recorded at -20 dBFS, so they would play at 85 dB.

Ah, gotcha. Don't we need to know the pitch of the tone to make the appropriate correction to the SPL meter's reading?

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post #747 of 777 Old 09-16-2010, 11:22 AM
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Originally Posted by BIslander View Post

Thanks for that clarification. I did not realize that the gain was being applied after the DAC, although that makes sense.


Set it at the reference point for your system - 0 dB if your master volume uses that kind of scale.

Theaters calibrate to 85dB, which is very loud. I think home calibration discs are generally designed for 75dB.

Not sure what you mean here. Calibration discs control the frequencies and levels of the tones.

Not at all. I often learn new stuff in these discussions.

Thanks. The Krell just uses a 0 - 50 (or something - never maxed it out) scale, where 0 is silent. Should I just use an arbitrary level - like what I use for normal viewing?

What I meant by using a different level of tone for the sub was a lower frequency; I mean, you can't use a 120hz tone to calibrate a sub, can you?

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post #748 of 777 Old 09-16-2010, 12:17 PM
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Originally Posted by win200 View Post

Ah, gotcha. Don't we need to know the pitch of the tone to make the appropriate correction to the SPL meter's reading?

No. That is taken care of by whomever created the test signals. But as I mentioned earlier, not all use the identical noise spectra, so there can be variation in the readings from different discs, or vs the internal cal noise. It's not an exact science when doing absolute level cals, but it is very repeatable for doing comparisons.

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Originally Posted by win200 View Post

Thanks. The Krell just uses a 0 - 50 (or something - never maxed it out) scale, where 0 is silent. Should I just use an arbitrary level - like what I use for normal viewing?

For absolute level cals, use the Krell's noise. That would most likely disable the master volume control so it is always "right" (I presume 75 dB). See what the manual says. Some processors do not bypass the MV, and instruct you to set it to s certain value.

Once you have the absolute levels set, then you can use the test disc to match the relative gains in the various channels. In that case, it does not matter where you set the MV control, as long as the noise is loud enough to overcome ambient noise and get a reliable reading.

Quote:


What I meant by using a different level of tone for the sub was a lower frequency; I mean, you can't use a 120hz tone to calibrate a sub, can you?

No, you cannot use any single sine wave tone for acoustic SPL measurements.
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post #749 of 777 Old 09-16-2010, 02:35 PM
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Alright, last question (I hope/think)...

With regard to the subwoofer, my understanding is that I don't have to worry about specifically turning any setting in the Krell up 15db, but that will be taken care of when I use the SPL meter and adjust it to 75db?

I'm also still confused about what the SPL correction tables are used for.

And Roger, that's an absolutely gorgeous theater. I love the displayed gear... I know this sort of thing is subjective, but I love having my equipment out to be admired. I've got B&W 800-series speakers, and I think they're too lovely to hide. (My wife stridently disagrees, however.)

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post #750 of 777 Old 09-17-2010, 10:45 AM
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Originally Posted by win200 View Post

Alright, last question (I hope/think)...

With regard to the subwoofer, my understanding is that I don't have to worry about specifically turning any setting in the Krell up 15db, but that will be taken care of when I use the SPL meter and adjust it to 75db?

I'm also still confused about what the SPL correction tables are used for.

And Roger, that's an absolutely gorgeous theater. I love the displayed gear... I know this sort of thing is subjective, but I love having my equipment out to be admired. I've got B&W 800-series speakers, and I think they're too lovely to hide. (My wife stridently disagrees, however.)

Thanks!

The SPL correction tables?

PM sent.
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