LFE in a stereo downmix

[dasdoing]

So the first question is whether Equalizer-APO already has a +10dB adjustment built-in for the LFE channel when you give it a mix equation. If it is aware of what LFE is, and that it is a louder signal then it may well do.

That would make more sense than a belief that VLC would be doing an adjustment.

Edit: A bit of research doesn't show any evidence that there is a built-in 10dB adjustment. Here I see someone doing the opposite-direction 10dB adjustment manually in a bass-management filter:

Eval: crossfreq=120
Copy: BASS=L+R+C+SL+SR
Channel: L R C SL SR
Filter: ON HP Fc `crossfreq` Hz
Filter: ON HP Fc `crossfreq` Hz
Channel: BASS
Filter: ON LP Fc `crossfreq` Hz
Filter: ON LP Fc `crossfreq` Hz
Copy: LFE=LFE+-10dB*BASS

while I meassured the peaks I obviously disabled everything in EQ-APO.

just did it again, this is the scene. the number is the max (not full 0dBFS) that just ocured. it is when the bad guys car crashes into them to stop them at the square. just before the shooting

and this is the other scene I was refering to

here the LFE is actualy only active on 3 shots of the the dozens he shots at the window

 

[edechamps]

What does "apply the necessary attenuation" entail?

In that bass management snippet above, someone is just adding channels willy-nilly. Is it using a "wide" or floating-point intermediate internally, so that's not a problem, you just need to make sure the final output result to the system doesn't clip?

(The convention I usually see in home theatre gear is that sub channels including bass management usually use a 15dB offset for the sub, so that last step would normally be

SUB=-5dB*LFE + -15dB * BASS

to help avoid clipping.)

Yes, this is what I meant. Basically, when one downmixes to stereo, it might be wise to ensure the resulting signal won't clip due to excessive summation.

 

[Andysu]

while I meassured the peaks I obviously disabled everything in EQ-APO.

just did it again, this is the scene. the number is the max (not full 0dBFS) that just ocured. it is when the bad guys car crashes into them to stop them at the square. just before the shooting

View attachment 189933

and this is the other scene I was refering to

View attachment 189935

here the LFE is actualy only active on 3 shots of the the dozens he shots at the window

can you, please show me pictures of your av system and speakers in the room as this scene puzzles me? thank you

 

[dasdoing]

can you, please show me pictures of your av system and speakers in the room as this scene puzzles me? thank you

I don't understand. These are digital peak meters meassuring the output (quasi)directly from VLC. my system is not relevant here.
I have no AV btw. I downmix and bass manage in Equalizer-Apo (which was disabled during the above)

 

[Andysu]

I don't understand. These are digital peak meters meassuring the output (quasi)directly from VLC. my system is not relevant here.
I have no AV btw. I downmix and bass manage in Equalizer-Apo (which was disabled during the above)

yeah i understand. thanks. i do it myself and you made me buy this movie that i hate it and arrives tomorrow and renting at present, because it vexes me.

 

[Andysu]

no time to really watching it LFE.1 to show the frequency range and dynamic range . spectrum lab, was designed for radio astronomy and has good use as spectrum analyzer for movies or music or test tones

i can playback about 90% of the in-room frequency response using LFE.1+Main on the avr so the LFE plays sounds on the same cinema grade JBL 4645/C subs. only problum with the rubbish film mix is the sound of the LFE in the scene has no doppler effect shifting sound of movement it is just a outdated LFE.1 that should be at least lot smarter by years ago to play these low freq effects so they have an actual movement of a sort? listening only to mono LFE.1, i can do this all day. how many other home cinemas actually listen to the sub/LFE on its own?
well let me break it down the LFE a single filtered effects channel can be frequency divided into multi subs to play only certain freq range and use another device to give a simulated stereo delay effect of sort may make the bond scene sound a bit more interesting?

 

[dasdoing]

no time to really watching it LFE.1 to show the frequency range and dynamic range . spectrum lab, was designed for radio astronomy and has good use as spectrum analyzer for movies or music or test tones

i can playback about 90% of the in-room frequency response using LFE.1+Main on the avr so the LFE plays sounds on the same cinema grade JBL 4645/C subs. only problum with the rubbish film mix is the sound of the LFE in the scene has no doppler effect shifting sound of movement it is just a outdated LFE.1 that should be at least lot smarter by years ago to play these low freq effects so they have an actual movement of a sort? listening only to mono LFE.1, i can do this all day. how many other home cinemas actually listen to the sub/LFE on its own?
well let me break it down the LFE a single filtered effects channel can be frequency divided into multi subs to play only certain freq range and use another device to give a simulated stereo delay effect of sort may make the bond scene sound a bit more interesting?

well, that kind of seams to match the peaks I got on the hit

this is a pure decoder, right?

how is the ongoing chain calibrated? professional RTA and stuff?

I told you that those 3 shots at the window with LFE make no sonic sense. even if the "right way" (read: intended) would be to have LFE 10dB higher, I would never do it...not with this movie at least.

now since the almost-full-scale on LFE seams to be in the encoded material, I have to wonder if this was realy mixed in a way propoused by the standard.


about the refrigerator (he-he-he). what kind of mic is this?

 

[Andysu]

it is complicated to explain how its all connected in the B-chain.
i think amazon hd version was peaking higher on the LFE as seem to recall it was like increase on the master fader of +2.4dB i started to see the LFE peaking at Over , the uhd seemed to be fraction less unless i have forgotten ? then again the movie was dreadful , the use of overhead surrounds is waste of time with this, it uses heights 1 2 and 3 but uses them for few minutes total out of the 164min running time.

 

[dasdoing]

it is complicated to explain how its all connected in the B-chain.

what I wanted to know is if your subs are calibrated 10dB(C?) above.

 

[mhardy6647]

Every time I do a quick visual scan ASR for "new posts" and see this thread, I misread downmix as dominatrix.

That's not... odd... is it?

Sorry for the digression. Carry on.

 

[dasdoing]

That's not... odd... is it?

no, Freud explained it

 

[Andysu]

what I wanted to know is if your subs are calibrated 10dB(C?) above.

i don't think they are and most times i think this +10dB boost is unnecessary for most unless you can see, i can see the channels on level meters and i go with what i see before i listen to it, depends i can mute the audio and just watch the level meters or watch level meters and much more besides that that is bit technical. so no i didn't use +10dB oh please, no, no don't roast me because i never used +10dB. so you saw the levels as it was more less, out of the rubbish denon avc-x8500h to my cinema processors and saw the levels that was frighteningly deafening and i had to make certain changes my sort of own THX/TAP but the movie was utter rubbish, and i can get back to watching listening to more serious movies like, Star Trek II the wrath of Khan. goodbye mr. bond rest in bits and pieces.

 

[dasdoing]

the circle of confusion is just x-times bigger with movie audio. the whole standard is crap.
if on our research we din't find clear answers, how do you expect the engeniers have them.

this guy actualy talked to a guy from Dolby about it: https://www.tvtechnology.com/opinions/more-about-the-lfe-channel-subwoofer

When a production monitoring environment is calibrated, the subwoofer itself is calibrated so that a band of noise between 20 and 120 Hz sent to it is measured to be 10 dB greater than the reference broadband level measured at each of the main speakers. These are each typically set at 85 dBC SPL.

now this is allready not acurate at all. it is not that c-weighting is flat. flater than a-weighting, but still:

this means 10dB higher on c-weighting doesn't equal to 10dB higher.
and the bigger problem I see is that the reading is also highly influenced by the frquency extension of the subwoofer. the lower it goes the higher the reading is, even if a sweep meassurement would show same levels.
calibrating with noises is just totaly flawed. good enough for PA, but not HI-FI at all

than there is this:

Note that it is the subwoofer that is being calibrated, not the LFE channel (which is not adjusted)

which means that it is not LFE that would need the boost, but the whole bass.
the more you look at it the bigger the circle of confusion gets.

and then you have this decoder manual:

If an RTA is not available, setting the subwoofer channel 4-6 dB high, as measured by an SPL meter, provides an approximate level. For example, set the subwoofer channel to 89 dBC SPL when the center channel measures 85 dBC.

it would be instresting to meassure what kind of curve this creates in reality. again, the c curve has a roll-off.

 

[digitalfrost]

I scrapped the whole +10dB thing a while ago and this only increases my opinion. You have to see, I use my system for everything, so having the 10dB LFE boost also required me to run everything at a -10dB preamp as to not clip in the digital domain. So that could go.

Also. Assuming you use your system for both movies and music, am I supposed to adjust the subwoofer level all the time? Or just render LFE at +4 or +6 based on assumption? For a normal system you would surely increase the LFE level so you don't have to touch the subwoofers all the time.

I am glad I have an RME interface, I can simply check the levels in Totalmix and make sure nothing clips.

 

[dasdoing]

I conclude that we should do the same we do with music's circle of confusion: using our ears and ajusting FR to taste. most will allready have a boost in the bass anyways (Harman)

 

[edechamps]

the circle of confusion is just x-times bigger with movie audio. the whole standard is crap.
if on our research we din't find clear answers, how do you expect the engeniers have them.

this guy actualy talked to a guy from Dolby about it: https://www.tvtechnology.com/opinions/more-about-the-lfe-channel-subwoofer



now this is allready not acurate at all. it is not that c-weighting is flat. flater than a-weighting, but still:

this means 10dB higher on c-weighting doesn't equal to 10dB higher.
and the bigger problem I see is that the reading is also highly influenced by the frquency extension of the subwoofer. the lower it goes the higher the reading is, even if a sweep meassurement would show same levels.
calibrating with noises is just totaly flawed. good enough for PA, but not HI-FI at all

than there is this:



which means that it is not LFE that would need the boost, but the whole bass.
the more you look at it the bigger the circle of confusion gets.

and then you have this decoder manual:

Personally I'd rather rely on ITU-R BS.775 which is a widely agreed upon international standard - it would be difficult to find a more authoritative source! The wording there doesn't have such ambiguities (emphasis mine):

The LFE channel is recorded with a level offset of −10 dB for the recording and exchange of multichannel sound programme material. This offset is compensated for in the reproduction system, where the LFE loudspeaker has an acoustic output (within its low frequency passband) of +10 dB with respect to the other channels, when fed by a signal whose level is equal to that of the signals feeding each of the L, C, R, LS and RS channels. The pink noise test signal is intended to be reproduced at an acoustic sound pressure level (within the LFE channel < 120 Hz passband) of +10 dB relative to any of the other individual channels. Note that due to the limited bandwidth of the LFE channel, if the acoustic level produced by the LFE pink noise is measured with a wideband sound pressure level meter, the reading will not measure +10 dB with respect to the other channels.

The acoustic level of the LFE channel should measure +10 dB within its < 120 Hz bandwidth when measured with a frequency selective meter. For broadcasting applications where signal levels are compliant with these specifications, the level of LFE channel should be reproduced with positive offset gain of 10 dB relative to the main channels on reproduction.

NOTE 1 – The film industry encodes the LFE channel such that a positive gain of 10 dB is required on reproduction and the reproduction level for DVD-Video is set to a positive gain of 10 dB relative to the main channels. However, the music industry, such as DVD-Audio or Super Audio CD, is currently coding the LFE channel such that zero offset gain is required on reproduction.

Given how many words are spent on the issue of measurement bandwidth in the above quote, it seems likely that the people who drafted the standard asked themselves the same questions you're currently asking yourself, and made sure the standard would not leave such questions open.

 

[dasdoing]

Personally I'd rather rely on ITU-R BS.775 which is a widely agreed upon international standard - it would be difficult to find a more authoritative source! The wording there doesn't have such ambiguities (emphasis mine):



Given how many words are spent on the issue of measurement bandwidth in the above quote, it seems likely that the people who drafted the standard asked themselves the same questions you're currently asking yourself, and made sure the standard would not leave such questions open.

great standard, but again, the question is: what did the engenier actualy do in his setup?
it is equaly problematic as the k-system for audio. great standard, but useless when nobody is using it

 

[Andysu]

oh, the stargate dtshdma lfe.1 has the level boosted +10dB so the bluray is fake, and even dts i think faked the boost on laserdisc dts jurassic park.
so if adding extra +10dB boost may result in possible blown damaged amp and sub drive.

i ran tests of stargate for few hours with my Cat, Bear, "this is as far as we've ever been able to get"

 

[KMO]

which means that it is not LFE that would need the boost, but the whole bass.

Yes, you're always calibrating the speakers (including the subwoofer), not the channels.

If you don't have bass management, then adjusting the subwoofer effectively adjusts the LFE level, because that's all it's playing.

If you do have bass management, then the LFE level is locked in during the bass management step, as it mixes the LFE and redirected bass into a combined subwoofer signal.

You should calibrate the subwoofer primarily to get redirected bass right, including integrating with the mains, then the LFE level will just come out correct according to the bass management.

AV receivers have a specific LFE level control which will adjust the subwoofer mix. Use that to adjust LFE, if you must. Trying to adjust the LFE via subwoofer gain will just screw up redirected bass.

The Dolby DP564 referenced in that article does not have an LFE level control, as far as I can see, so its bass management will be assuming the standard cinema +10dB.

 

[dasdoing]

I allready skip through the movie to find a loud scene before I watch it to calibrate loudness. I will just add the extra step of adjusting my subwoofer amp knob by ear. I might change this in the future but atm I feel that this gives me best results. it's not that because some producer thinks that gunshots have to have loud 20Hz components that I have to digest that