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3K views 26 replies 13 participants last post by  derrickdj1 
#1 ·
#2 ·
Thanks @LTD02

Let me see if I have it right:

The generally accepted definition of "Reference" when calibrating your setup = 0db on the master volume of the avr and should yield 85db spl at the main listening position when a -20dbfs signal is played through each channel except for the lfe channel which should yield 95db.
 
#9 ·
Thanks @LTD02

Let me see if I have it right:

The generally accepted definition of "Reference" when calibrating your setup = 0db on the master volume of the avr and should yield 85db spl at the main listening position when a -20dbfs signal is played through each channel except for the lfe channel which should yield 95db.

yes, that is what some folks would say.

other folks would say that because of how we perceive loudness the measured spl level for "reference" should be a function of our room size. the relationship between the room size and the target reference level are in table 13.4.
 
#3 ·
@LTD02 — John, can you please clarify the 126db requirement for LFE when all channels are redirected to the sub?

I've always aimed for a system that can do 108db on all speakers and 130db at 20hz (accounting for headroom) to ensure I can hit proper reference. If 115db was only the goal, I could have stopped 6 Marty's ago.

Sent from my SM-N910W8 using Tapatalk
 
#4 · (Edited)
I think I pulled out the relevant conversation from the last thread to get it located in one place. There was a lot of muddying posts in that thread, so I didn't copy them over. If I missed a good one I apologize.


Do you not?

Reference is called Reference for a reason... It's what the sound engineers wanted you to hear at the volumes they wanted you to hear them at.
Clarification point. Reference as defined by THX doesnt account for Reference in a commercial cinema vs a home cinema or have any deviation for room size. Reference for THX (which is the original standard) is simply 85dB with a -20dBfs test tone for main speaker with 20dB headroom for peaks for speakers as measured at the listening position (105dB). and 85dB with 30 dB of headroom for peaks for subwoofers. (115dB)

THX standards don't speak to rerouted bass levels that may require additional headroom from the sub over the 115dB number.

And as to home theater AVRs using 75dB as the rest tone level that isn't because home theater reference is lower spl than commercial, it is because the AVRs are programmed to use - 30dB as the calculation point for the 0dBfs instead of -20dB. This is a decision to avoid jarring home owners with test tone volumes at 85dB which are actually quite loud sounding, and even to avoid damaging some lesser speakers or speakers placed at long distances during test tone auto AVR setups. But THX reference as originally defined is the same regardless of home vs cinema, it's simply accounted for and auto calibrated back to 85dB internally on the home theater AVR.
Listening to reference means the dynamics will hit 105db not normal voices and noises calibrated to 105db at MLP. That would be +20db or +30db depending on how the system is calibrated. Content has 20+db swings of dynamics which make the calibration work out.
You are correct. However, THX Certified Releases are supposed to all be mixed to the same level. Many throw out the THX Reference Level of 85 dB with a -20 dBfs bandwidth limited pink noise, but forget to include that THX Reference Level only applies to THX Certified Releases.

There are movies like Open Range that are mixed with the average dialog level about 10 dB under a THX Certified Release. This is to allow for louder peaks when listened to at levels comparable to other movies. It then gets only 2 stars at data-bass.com for Level when in reality it is louder than most other movies. This isn't taken into consideration when comparing waterfall graphs, either.
The Fletcher Munson Curve (below) illustrates that when listening to music through your speakers/subs, as the actual loudness changes, the perceived loudness your brain hears will change at a different rate, depending on the frequency. Each equal-loudness contour on the graph represents a measure of sound pressure (dB SPL), over the frequency spectrum, for which a listener perceives the SAME level of loudness when presented with pure steady tones. The unit of measurement for loudness levels is the phon, while the unit of measurement for sound pressure levels is the decibel. Our ear is more sensitive to mid range frequencies, less sensitive at the top end, and much less sensitive at the ULF frequencies covered by the subwoofer. Therefore:


  • At low listening volumes – mid range frequencies sound more prominent, while the low and high frequency ranges seem to fall into the background.
  • At high listening volumes – the lows and highs sound more prominent, while the mid range seems comparatively softer.



In the example below sounds A, B, C and D all have the same sound intensity of 65dB. However, this does not imply that they have the same perceived loudness to the human ear. Sounds A and D have the same loudness since both are on the same equal loudness curve as having a loudness of 60 phons. Sound B is above the 60 phon curve, so that implies that it would be perceived as louder than A or D. Sound C is the loudest of the four sounds since it shows the greatest displacement above the 60 phon curve.




140 dB at 20 Hz is approximately 30 dB below the threshold of pain, while the same 140dB at 1 khz would be intolerable.




Conversely, a subwoofer system putting out 135 dB sound pressure at 20 Hz would be perceived to be at the same loudness as the main speakers putting out 110 dB at 1 khz.(see below). I have heard the Seaton Catalyst 12c's and they were capable of 110dB sound pressure levels. Maybe you can't hear them because their output is being masked by problems with room modes. Check out the MiniDSP DDRC88A with the plug in for managing multiple subs for a possible solution.

https://www.minidsp.com/products/dirac-series/ddrc-88a


At what speaker ? Or efficiency? You are missing a critical piece. Its just a guide based on typical.
Doesn't matter. That's the beauty of the SPL standard. It is designed to get the same volumes (Audio experience) out of very differently designed speakers in you main listening position and help eliminate those variables. Yes you'll need more power for some speakers with lower efficiency. Yes most speakers will NOT be capable of THX reference volume levels in a larger room (many won't be capable of such even in a smaller room). A speaker that can play reference levels in a smaller room may not be able to play reference levels in a larger room.
(SPL diminishes with distance)

Reference calibration SPL trims are (of course) calibrated to the main listening position.
Found it http://www.thx.com/consumer/thx-technology/thx-reference-level/

0db or 0mv = 85db + 20db headroom. Dang, all this time I was mistaken!
I read the Atmos pdf and I'm reasonably sure it says each height speaker is supposed to be 105db capable as well.
The Dolby's Reference Atmos processor box supports up to 64 discrete speakers. (It costs like $40k and comes with it's own Dolby technician...)

Lot more than 126db in-theory, although I highly doubt you'll ever find a place with a full 64 implementation and a movie demanding all 64 to 0dbFS.

I'd bet most locations are doing only 4 to 8 discrete height tracks, and throwing them at horizontal rows of speakers or quadrants whom's total sum is 105db directly underneath 'em.
(...Just a gut feeling ;))

I have no idea how AVR's are downsampling Atmos heights to the base channels, or if they just ignore those panning-objects altogether when set to none. My guess is: ignore, as that is easier to code (i.e. no coding needed ;)).
Very wrong!

No one in the thread has been right yet. Dolby's analog test tone was mis-measured by 2dB due to non-RMS SPL meters back in the day. As a result, now their digital systems are set to 85dB with a -18dBFS signal for consistency. However, dBFS as they use it is not a true RMS dBFS measurement either. It has a 3dB offset so that a full scale amplitude sine wave measures 0dBFS rather than -3dB which is the true RMS measurement.

So, the peaks are 106dB for mains and 116dB for the sub(s).

Edit: Note the max SPL of a sine wave is 103dB.
It's not very incorrect for sure. All that matters is that peak dbs are all set to 105/106db at the MLP anywhere on the MV knob as long as it's known and the LFE set aprox 10db higher if preferred at the same MV setting. As long as one sets the gain structure properly then it makes no difference what the MV number is. There are many ways to go about setting up reference MV numbers but it's not playing peaks above 105/6bds at the MLP. Peaks above 105/6dbs at MLP would be considered xdb above reference levels.
good catch. :)


and there is more...one problem is that thx doesn't spec 'reference level' in the first place. that is set by the smpte (Society of Motion Picture and Television Engineers) for commercial cinemas where the 2/3 seating position spec is the 85/105db everybody is talking about.

for homes, small room mastering studios, the standards for output, dialnorm, dynamic range compensation, speaker placement and all the rest of it come from the atsc (Advanced Television Systems Committee). recognizing that small room acoustics are very different from large room acoustics, the atsc had to come up with a whole series of "reference levels", which are shown below. i wouldn't be surprised if a future iteration of the spec were to include some consideration of room treatments or other sound absorption factors.










http://atsc.org/wp-content/uploads/...tablishing-and-maintaining-audio-loudness.pdf
John,

THX does spec reference as 85dB with 20dB allocated for headroom here. It was linked from THX's website a few posts back. You are stating they don't say that is for home use but it clearly is talking about home use here.

http://www.thx.com/consumer/thx-technology/thx-reference-level/

More references:

http://hometheaterhifi.com/volume_13_1/feature-article-thx-1-2006-part-1.html

http://www.acousticfrontiers.com/2013314thx-reference-level/

http://www.audioholics.com/frequent-questions/how-to-manually-level-match-speakers


The ATSC standard, in my opinion, does not replace the THX standard. It is arguably a different standard. If it was accepted by THX (which is credited with creating the Reference standard) than THX would revise their standard in their documentation. Let me know if you disagree.

As far as the 105/106 discussion. That's news to me and is interesting, but seemingly not that consequential in the end.
thanks jon. what thx calls "reference" is not a recommended listening level in the same sense that "reference" is a target listening level in a professional cinema as defined by smpte. rather what thx calls "reference" is an equipment performance specification. this is why thx has several different levels of "reference" (select, ultra, etc.) instead of just one. the confusion between the two concepts has confused the whole world.
Here, I disagree with you my friend.

When people say "Reference" isn't it fair to say they are typically talking about the 20+ year old "Reference" standard as defined by THX? 85dB at MLP with 20dB reserved for dynamic headroom.

Clearly a standard reference listening volume requires different amounts of capability based on room size and MLP distance.

http://www.thx.com/consumer/home-en...ter/thx-certification-performance-categories/

The different ratings, select, ultra, ultra 2 speak to capability of both speaker design and power requirement as related to size of room and distance to main listening position --- it helps signify to the consumer what is required to drive the equipment to the established THX defined Reference level of 85dB with headroom for 20dB peaks.

A smaller, less capable, less sensitive speaker may be able to hit reference level audio in smaller room with a close main listening position. Thus a select cert is appropriate where that same system could not achieve reference in a large room with a more distant MLP. That room may require a THX ULTRA II cert within their hierarchy. That is what the THX labels mean. (For example In some cases a specific quantity of subwoofers was needed on a particularly labeled subwoofer to achieve the THX label - a THX rated Crystal Accoustic subwoofer was one such instance I crossed paths with --- the documentation stated it required four of the 12" subs to achieve the THX Ultra II branding. http://www.avsforum.com/forum/113-s...hs.html#/forumsite/3207/topics/1408856?page=1 )



The THX cert labels are just one way of trying to inform a consumer of what level (quantity) of matching gear is likely needed to try to achieve a standardized SPL listening level for cinema.

Is it fool proof? No. Is it universal no. Is it a money/branding/marketing grab? Yes.

Has there been a better, more widely accepted proposal in the last two decades from another vendor? Not that I'm aware of.

You know all this


My hope in my posts on this is to inform some of the "reference is whatever my preference" type posters in this thread, as well as the wild SPL confusion that various posters have dumped into this thread. Reference has been defined for decades. It may not be meet all peoples' preferences (too loud, too soft, too generic, not addressing subsonic frequency, or hearing curves, or any number of personal insults to ones personal audio preferences and subjectivity) ------ and yes it is not used universally by studios in mixing.


But the lack of universal following of the standard doesn't change what the standard is.
These 2 posts get the gist of it correct. There will always be some further mess from different dialog normalization settings in different formats, but I'm baffled how a simple SPL to Volume knob calibration can be so misunderstood.

There is the concept and the reality have some deviation, but it's more important to understand the concept and it's limitations in the real world. The concept of the reference level calibration was to insure that a known recorded level from a given channel produced a given SPL at the listening position. This has always been done with band limited pink noise, assuming similar acoustics, flat frequency response, and minimal distortion at the maximum recorded levels. Those 3 assumptions vary and do not always hold true. We then have some complication of dialog normalization and differences between Dolby and DTS here as well. An averaged signal like pink noise is significantly impacted by room acoustics, which also impacts the perceived loudness of typical program material after this signal calibration.

In the end it's a good point of reference, and that's it. There are many complicating factors, and many variables that would make "reference level" sound very comfortable in one room and painfully loud in another. That observation usually ends up telling us a lot about a system and the acoustics, and combining a reference volume setting with other info can give us an approximate concept of the volume levels or peaks being reproduced. If someone tries to get hyper particular about the exactness of "reference level" in real rooms, they likely don't understand it. ;)
It's not 105dB peak, it's 108dB peak. 105dB would be the maximum SPL of a sine wave, which is not peak. There's 3 more dB of output possible if it was set to 85dB with a -20dBFS signal. However, as I pointed out Dolby introduced a 2dB error somewhere along the way which makes it only 103/106dB.

BTW, REW, at least as of a year ago, did not measure it's signals per the IEC/AES standard used in professional audio. Professional audio has a 3dB shift so a full scale digital sine wave measures 0dBFS. REW measures in absolute RMS. Meaning when you set it to generate a -20dB test tone you're not getting a -20dBFS test tone, but a -17dBFS one.
i used to think the same, but over the years i kept trying to find the technical documents that detailed the supposed "thx reference for home theater" and ultimately what i discovered was...there aren't any. holman has even commented on the lack of standards for home theater.

there is no thx "reference" listening level for home rooms. output capability is being mixed up with suggested output levels. those are very different concepts. thx speaks to the former only for home theater.

thx had input into the smpte "reference" level but was not responsible for defining it for commercial cinemas. that and the fact that all the theaters that were "thx certified" seems to have generated a circle of confusion.


also, thx never released their specifications for what defined "reference" either. it has always been a proprietary method for rating equipment and theaters and has morphed over time and from theater to theater. most theaters wanted to be "thx certified" but didn't want to buy new equipment and of course thx wanted the licensing revenues. this is in part why there is so much confusion over what it is.


the same problem arises with dolby specs. for cinemas, they suggest the smpte "reference" standard 85/105db 2/3 of the way back in the theater.


for atmos at home, they don't have a "reference" because none exists. they recommend something in the range of the atsc home "reference" points. in the current atmos for home calibration document, they suggest something in the range of 79-82, depending on room size (and not mentioned...other stuff). using whatever point the listener then picks as their "reference", they should have 20db of headroom. no disagreement there as that is what is required to playback the content without clipping.





http://www.dolby.com/us/en/technolo...tmos-home-theater-installation-guidelines.pdf




atmos cinema. here they are following the smpte standard of 85/105db because "reference" is defined, though they kind of back pedal a little bit for the mids and highs, just to help more folks get over the line. i don't know if those reduced output requirements are part of the smpte spec or not because in order to find out you have to purchase their document.





http://www.dolby.com/uploadedFiles/Assets/US/Doc/Professional/Dolby_Atmos_Specifications.pdf
sorry, just one more bit from the man himself.


@Archaea
p196, holman, 2012.








i was kind of waiting for that. sorry bud. :)


if there is anything more to say on the reference stuff guys, lets take it over here:


http://www.avsforum.com/forum/155-d...5-reference-discussion-cont.html#post47008289

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so if there is anything left to say, blast away.
I still disagree.
(which probably means I'm wrong --- if our past debates are taken into account)
Never the less, all those other variant standards you linked don't change THX reference standard. (as far as I can see THX still specifically lists 85dB and 105dB at current)

One of the THX website links shared clearly lists 85 dB average and 105 dB peaks as the standard for home consumer use, just like commercial cinema.
http://www.thx.com/consumer/thx-technology/thx-reference-level/

THX is the oldest/first/and most well known - it is the only of these different standards built into the auto AVR setup functionality that I'm aware of --- specifically in THX certified AVRs, and it is generally the standard applied to commercial cinemas for decades. (various shortcomings or not). I submit it is the back of the mind reference to most people on this board.
----------------

Frankly, it feels like weaksauce to have a "range" of acceptable SPL at the listening position for a reference SPL standard. 85dB at the MLP might seem too loud to some people - if so that's their preference. Their preference should not change a reference. A individuals preference can deviate from a reference at will - but a reference should be a set value. Preferences can be dictated by toooooooooooo many variables to mean anything. We need a reference.

With some of the flexible room size based standards - it seems, a ~6dB range (double, or half the volume) isn't an ideal standard. There is already a big range of variance even if attempting to unite around a single 85dB reference point because of any number of factors from speakers, to room placement, wall and floor coverings/absorption, to EQ application. Further broadening that target by another ~6dB of accepted variance based on a room size flexing standard is how we further compound this nonsense.






http://www.avsforum.com/forum/90-re...mparison-g2g-november-8-2014-kansas-city.html

The above capture is an autoeq routine test we did on multiple AVRs with fixed and identical speaker placement. We measured each AVR after their default auto EQ calibration using the omnimic on a fixed mic position at the MLP at -12dB on the main volume dial (arbitrarily chosen fixed volume to compare each AVR that wouldn't blow our ears out while we were capturing the sine sweeps all day). This is the sorry state of calibrated reference as delivered by autoeq functions today. There is no way someone could say they had an equitable viewing experience to the next guy with that kind of variance. We need a stricter standard applied to our equipment. This test was all in the same room with identical speakers and subs for each test and fixed mic positions. The results would even be more variant switching rooms and setups.

Sickening...
 
#20 ·
The above capture is an autoeq routine test we did on multiple AVRs with fixed and identical speaker placement. We measured each AVR after their default auto EQ calibration using the omnimic on a fixed mic position at the MLP at -12dB on the main volume dial (arbitrarily chosen fixed volume to compare each AVR that wouldn't blow our ears out while we were capturing the sine sweeps all day). This is the sorry state of calibrated reference as delivered by autoeq functions today. There is no way someone could say they had an equitable viewing experience to the next guy with that kind of variance. We need a stricter standard applied to our equipment. This test was all in the same room with identical speakers and subs for each test and fixed mic positions. The results would even be more variant switching rooms and setups.
Sickening...
Thanks for the data. I sort of assumed this would be the case. Hence why I have NEVER and will NEVER trust auto-anything. Be it EQ or cars. :D
(If you want it done right, you gotta DIY... etc etc)
 
#6 ·
@Archaea

thanks for pulling all those posts together. i wasn't sure if anybody was interested to continue the conversation.

we will have to agree to disagree on this one. :)

a few repititions/clarifications:

- i'm not sure if it was made clear in my quotes of those books, but those are from thomlinson holman (the audio engineer who co-created thx).

- thx never created a standard for 'reference' level. the cinematic standard was created by smpte. thx had input into that, but smpte is provides the standard and full technical information. thx then created several work-arounds for folks who were trying to get their movies to sound right in the home, but none of them were ever released in any sort of a technical standard.

- movies are mixed/mastered on various size stages ranging from nearfield setups to large dub stages that approximate medium size theaters. the audio experienced by the author in those environments is very different even if the spl level is measured the same. so even if some number, such as 85db were chosen, there would be no translation of the author's intent from one mastering environment to another or from one playback environment to another. what you are hoping for is a rosetta stone. while i agree such would be ideal, as a practical matter, it isn't possible.

- compounding the point above is that many studios create "home mixes" of their theatrical content. changes in dynamic range, width of panning, output levels, equalization, etc. may all differ from the theatrical release. this is a good thing in most instances, but it further compounds the translation problem. recall that part of the original thx processing was "re-eq". the purpose of that was to bring down the top end so as to make movie content more listenable in the home. the amount and nature of the re-eq was not public information, so again not a standard. a problem now is that thx processors that include re-eq are still bringing down the top end despite many studios doing the same in their nearfield (home) blue-ray releases. there is no way to know if it has already been done or not, so in some cases re-eq makes things better, sometimes it makes things worse (because the problem that it solves has already been corrected upstream). holman has thrown his arms up in the air with respect to that one too.
 
#14 ·
I use the processors test tones to set trims and then measure with REW to set the MV level. I just run a -10 dBfs sine sweep. If I have the MV on -10 dB then I look for a sweep of 85 dB and you don't want too many dips and peaks or some parts will be low or low, this is where EQ comes in if needed. If the measured sweep was 95 dB the MV reference is -10 dB. My reference viewing is never too loud set this way. IMAX is louder than my room at reference an I need to run about 5-6 dB louder to be about the same loudness subjectively.
 
#24 · (Edited)
Hi,

I was late to this party, but enjoyed reading the discussion. There have been other threads in which several film mixers have stated that 0.0 MV (Reference), for movies they have mixed, sounds loud to them in their personal home theaters. This is for the small room effect reasons observed by Holman, and cited by LTD02. They consequently said that they usually watch movies at about -5 MV.

One additional point which has been skirted, but not addressed directly, is the difference between the sum of 7 speakers playing at 0.0 MV, and only 5 speakers. A 7.1 system should measure slightly louder at the MLP, than a 5.1 system, at the same MV, in the same room. I believe I remember reading that the difference would be about 2db.

I particularly liked Mark Seaton's post, and LTD02's posts, that explained that Reference volumes are actually a bit of a chimera in home theaters, depending as they do on so many variables, including things like size of room, room treatments, bass boost, and number of speakers. The Reference standard gives us a great starting point in calibrating our systems, and understanding their objective capabilities. But it is doubtful if any random two of us, listening at exactly the same MV setting in our respective home theaters, would measure, or perceive, exactly the same SPL.

Regards,
Mike
 
#25 ·
Thanks guys for a very informative thread.

I will aim for 75dB in my HT.
 
#26 ·
the other night i was reading through "The Recording Academy's Producers & Engineers Wing: Recommendations For Surround Sound Production" (trying to find out what content goes to the 4th and 5th screen channels when 5 are used) when i happened to notice a recommended "reference" range.

i don't know much of anything about the producers and engineers wing of the recording academy, but according to the document itself:

"The Recording Academy's Producers & Engineers Wing consists of more than 5,000 members, including many of today's leading surround sound practitioners. It is our intention to provide a comprehensive set of guidelines and recommendations for the production of music and other types of audio (such as film and video postproduction, gaming, etc.) in surround sound."

image from the document:



http://www2.grammy.com/pdfs/recording_academy/producers_and_engineers/5_1_rec.pdf


so at least according to these guys, the authors of the content are "referenced" to 79-85db.
 

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