LFE level for SACD conversion

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alek2702

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I've been wondering what the proper LFE level is when converting SACDs to LPCM for playback in my home theater, hoping you guys have more experience with this.

If I understand correctly, Dolby, DTS and LPCM tracks get their LFE signal boosted by 10dB by the AVR while DSD should not. So when converting DSD to LPCM, it'd make sense to lower the LFE signal by 10dB to avoid a bass boost on playback after conversion and get the original level back. Then again, I've heard it's not a rule as there are SACDs authored out of spec and LFE might already be lowered for home theater playback.

Since it was mainly David Bowie's Heathen SACD that got me thinking, and it's not been released in another surround format to compare, I thought I'd check his Reality SACD and compare it with the DualDisc version I have, since it's also a Tony Visconti mix from the same time period.

As you can see below, it seems the LFE level is roughly the same for both SACD and Dolby Digital mixes (barring a very slight difference caused by a different cut-off point for the low-pass filter):

1) SACD (level matched)
1642267028491.png



2) DD
1642267063290.png


Am I right in thinking one of them is incorrect? Either the SACD LFE is missing the 10dB boost when played back on a DSD machine, or the Dolby is 10dB louder compared to the SACD when the boost is applied by the AVR.
Is there any way to gauge which is more likely? Looking at the LFE signal, it does peak around 5dB lower than the fronts but not sure how much that means.
 

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DSD is just a digital recording format like PCM and treated no differently with regards to channel levels. The +10db offset for Lfe channel calibration is simply how .1 Lfe channels in surround systems are calibrated. This is the standard calibration and recorded music mixed in surround is intended to be played on a calibrated system to be heard as intended. Weather it be stored to PCM digital or DSD digital.

There may be one-off cases of Lfe channel mis-calibration. There are in fact even confirmed cases of mains channels being swapped around in older quad releases! There are phase issues reported for a handful of surround mixes with the Lfe channel being phase offset. Heck, we have volume war and treble blasted masterings in the surround world that are beyond damaged!

The calibration of the Lfe channel is supposed to be across the board though and DSD format (SACD) isn't doing anything non-standard.
 
Thanks for getting back!

I've seen it mentioned a couple of times (here in the forum even) that DVD/BD and SACD are/should be mastered differently due to the 10dB LFE boost that happens with 'movie' formats only, so thought there's something to it. Foobar's SACD plug-in also has an LFE setting where you can lower/boost the signal by 10dB and I think I remember the developer explaining it the same way.

Here's @ssully's post on this: Extracting music from multi-channel discs
Re DVD vs SACD LFE, in a nutshell:

DVD (and DVDA) LFE *expects* a +10dB boost before analog output to the subwoofer.
SACD LFE (*if* mastered according to SACD spec) does NOT. It 'expects' to be output 'as is'.

If your system doesn't 'know' this, you get wrong SACD LFE output level.

And if your system *does* know this, but the SACD LFE is not mastered to SACD spec..i.e., if it is mastered like a DVD -- again the LFE output level is wrong.

Handling this all in software (software converters, software players) adds another level of either confusion or opportunity to get it right, depending on your outlook.

Happy trails. ;)


Still, the Bowie example I posted earlier certainly doesn't adhere to that so I should probably take my mind off it and enjoy my Heathen rip as is ;)
 
There isn't supposed to be a difference between movies and music. This came about using the reference pink noise source to calibrate this low band restricted channel. Think of it as "how the Lfe of any .1 system is calibrated" rather than "a boost".

Having said that, there are and will continue to be mixes that go wild with the Lfe channel and a lot of them will be movie mixes.
 
Not my point at all to argue ;) just wondering then if I misunderstood what was said in the other thread or was that information incorrect?

Here's another post that mentions the 10dB playback boost for home video formats that's not expected with SACD (hence the confusion when converting SACD to a home theater format):
Btw I would not necessarily lower LFE by 10 db when converting SACD to PCM.

In a perfect world
-- all DD/DTS/DVDA LFE (as per spec) discs would be 'printed' with -10dB LFE offset relative to other channels, and thus to properly play back, a +10dB boost will be added to the LFE somewhere down the line.
-- all SACD (as per Scarlet Book spec) discs would be printed with NO LFE offset, and thus to properly play back, no boost is applied later.

(But it was already an imperfect world when we *weren't* ripping SACDs. Potential incorrect LFE levels when using analog vs digital connection, decoded versus nondecoded, SACD vs PCM......remember the LFE Bug? For an overview of the potential pitfalls, see https://www.avsforum.com/forum/91-a...7-lfe-subwoofers-interconnects-explained.html)

In a perfect world, where SACD LFE was always printed 'as is', and because AVRs tend to 'expect' PCM LFE to be down by 10dB and thus apply +10dB to LFE (the legacy of DD/DTS), we would always be right to *lower* LFE of SACDs when converting to PCM. (The AVR after all has no idea what the source of the PCM data was.)

But in the real world, anecdotal evidence suggests that not all SACDs have been mastered according to spec. Sometimes their LFE was already 'printed' low, like a DD/DTS/DVDA disc. In this case we would not want to lower it yet again.

see near the bottom of this page, about the Pentatone SACD calibration disc:
https://bobpariseau.com/blog/2018/4/28/calibration-discs-you-need-these?rq=SACD
The question is, how can we determine what the 'right' LFE level is?
One possible way is to compare an SACD rip, with no LFE boost or cut applied during file creation, to a ripped DD or DTS (or maybe DVDA) release of the same mix. This presumes that the LFE level on those is 'correct'. I've done some of this and the data are...messy. It really requires a deep dive that I haven 't yet have time to do.


This is all a great argument, in the end, for not even using the LFE channel in multichannel music mixes. Put your non-explosive bass in the 'regular' channels and let bass management send it to the sub! Done! (This is Bob Katz's view too)
 
I've been wondering what the proper LFE level is when converting SACDs to LPCM for playback in my home theater, hoping you guys have more experience with this.

If I understand correctly, Dolby, DTS and LPCM tracks get their LFE signal boosted by 10dB by the AVR while DSD should not. So when converting DSD to LPCM, it'd make sense to lower the LFE signal by 10dB to avoid a bass boost on playback after conversion and get the original level back. Then again, I've heard it's not a rule as there are SACDs authored out of spec and LFE might already be lowered for home theater playback.

Since it was mainly David Bowie's Heathen SACD that got me thinking, and it's not been released in another surround format to compare, I thought I'd check his Reality SACD and compare it with the DualDisc version I have, since it's also a Tony Visconti mix from the same time period.

As you can see below, it seems the LFE level is roughly the same for both SACD and Dolby Digital mixes (barring a very slight difference caused by a different cut-off point for the low-pass filter):

1) SACD (level matched)
View attachment 75225


2) DD
View attachment 75226

Am I right in thinking one of them is incorrect? Either the SACD LFE is missing the 10dB boost when played back on a DSD machine, or the Dolby is 10dB louder compared to the SACD when the boost is applied by the AVR.
Is there any way to gauge which is more likely? Looking at the LFE signal, it does peak around 5dB lower than the fronts but not sure how much that means.


What were the LFE settings when you converted DSD to PCM?
 
What were the LFE settings when you converted DSD to PCM?
LFE set to 'as is'.

Also checked two other releases I had on hand- NIN The Downward Spiral (SACD vs DualDisc), and one of the Depeche Mode remasters (SACD vs DVD-V).
Other than no/different low-pass filter on the SACD side, they had the same levels for LFE.

For the DVD versions, I compared both ac3/dts->wav conversion (done with eac3to) and direct ac3 rip.
 
My suggestion would be to leave as is, but if you find too much or not enough bass change the setting for that particular disc.
 
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