LFE 10dB attenuation and boost

[Beber]

Gemini also explained to me that for a PCM track directly played from a disc on an actual Blu-ray player there's an electronic HDMI thing occuring that does trigger the 10dB boost on the LFE. It’s an industry agreement that allows that PCM LFE to be boosted even without an implemented metadata flag to trigger it. However, if you play a rip, even a 1:1 ISO copy of said disc through a media player, it won’t boost the LFE. So there's a distinction to be made between a professional PCM track and a more personal PCM track. All PCMs are not created equal, so to speak. Or not decoded equal to be more precise. So basically, if you play an old Disney Blu-ray disc with a PCM 5.1 track, like a "Pirates of the Caribbean", on an actual Blu-ray player, the LFE will be boosted. However the same untouched track played from a Blu-ray rip through a PC, Zidoo, Zappiti, etc. will not have the LFE boosted, so even in that case, we should modify the track to boost the LFE natively directly on the track to compensate the 10dB deficit.

[stwd4nder2]

Gemini also explained to me that for a PCM track directly played from a disc on an actual Blu-ray player there's an electronic HDMI thing occuring that does trigger the 10dB boost on the LFE. It’s an industry agreement that allows that PCM LFE to be boosted even without an implemented metadata flag to trigger it. However, if you play a rip, even a 1:1 ISO copy of said disc through a media player, it won’t boost the LFE. So there's a distinction to be made between a professional PCM track and a more personal PCM track. All PCMs are not created equal, so to speak. Or not decoded equal to be more precise. So basically, if you play an old Disney Blu-ray disc with a PCM 5.1 track, like a "Pirates of the Caribbean", on an actual Blu-ray player, the LFE will be boosted. However the same untouched track played from a Blu-ray rip through a PC, Zidoo, Zappiti, etc. will not have the LFE boosted, so even in that case, we should modify the track to boost the LFE natively directly on the track to compensate the 10dB deficit.

Is there a better source then gemini? Because without one I'm calling bullshit on that. I haven't noticed my AVR doing anything different playing PCM from a blu-ray compared to a rip or another PCM source. And I'd imagine this would be something commonly documented as it would cause problems when doing a manual calibration.

[Beber]

Well, Gemini is not really a source. It only searches for all the available data on the subject and synthesizes them to report them in an easier way to understand even for a non-expert. So it has to be documented somewhere. Gemini told me that whole thing was the reason why we can read some complaints on forums regarding a lack of punch in the LFE on concerts in PCM 5.1 for instance.

[stwd4nder2]

Well, Gemini is not really a source. It only searches for all the available data on the subject and synthesizes them to report them in an easier way to understand even for a non-expert.

It also just makes things up. LLMs are cool and useful but also extremely unreliable. Always ask it for a valid source and verify with said source, never take one at it's word.

[Beber]

It always indicates its sources. I'm just too lazy to read them since it's all too hi-tech for me anyway, so I'm fine with Gemini translating the explainations in simple words. I also discussed it with Gemini in separate threads and it always knows what I refer to without having access to earlier threads, so if it made it up once, I don’t think it would make the same stuff up each time, do you? Plus you said yourself the subject came up before, so there are precedents. But it is true that Gemini can make mistakes. I corrected it on some stuff I know for sure on other subjects, so I know it must be taken with a grain of salt. But on this subject, I don’t know too many stuff myself to spot where Gemini is wrong, so that's why I figured I would bring the subject to your attention, you guys. Hence my inquiry in the OP: is this common knowledge?

[ash_82]

From what I thought I understood about this, an LFE channel is an LFE channel. A FLAC track is decoded to LPCM by the player, and the AVR should apply the 10 dB LFE boost during playback, provided all the channels are properly mapped.

I’m not at home right now, but I could make a FLAC test track with a 50 Hz sine wave at -30 dBFS in the left channel, followed by the exact same 50 Hz sine wave at -30 dBFS in the LFE channel, with bass management enabled.

If the LFE signal measures about 10 dB louder at the subwoofer, that should confirm whether the +10 dB LFE gain is being applied to multichannel PCM in my playback chain.

[Beber]

So... this time I asked about it to Gemini directly on the Gemini site instead of the implemented Gemini in Google search, and it tells me it's false and a common mistake, and that all LFE channels from all codecs are being decoded and boosted the same way in any case, so this whole subject is apparently non existent now. It's a head-scratcher but more reassuring that way. So to sum up, forget about it: every ".1" will work the same and be boosted by the AV Receiver and thus don't need any boost implemented at the source. No distinction between official PCM out of the disc or custom made PCM track either.

You can still test your thing, @ash_82, but I guess you'll come up with the same conclusion.

[stwd4nder2]

I did some reading more on it, and somebody correct me if I'm wrong but this seems like it's more of a thing in ac3/DTS to aid compression then it is a something with playback/mixing. And the encoder/decoder should automatically take care of it.
At least that was how I read it. There seems to be a lot of confusion around it and most of the online talk about it is old and from the DVD era.

[Beber]

From what I think I understand, the LFE is attenuated by 10dB to avoid clipping. I don't know if it's during mixing or during encoding, like @stwd4nder2 says, that it's taken care of. Maybe that's where the confusion comes from: for Dolby and DTS, maybe it is during encoding that it's automatically taken care of by the encoder, but maybe not in PCM which requires that -10db implemented during mixing. Maybe that's where the first Gemini explainations got mixed up 'cause it claimed there was a difference between PCM and proprietary Dolby and DTS codecs. And during playback, it's compensated by the AV Receiver boosting the LFE no matter what codec comes through as they were all attenuated by 10dB at some point before playback anyway and the AV Receiver doesn't differentiate an LFE from Dolby, DTS, PCM or whatever. For the AV Receiver, all LFEs are treated equal without discrimination.