Understanding Sub Test Results - AVS Forum
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post #1 of 22 Old 08-24-2012, 07:50 AM - Thread Starter
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I've been reading a lot of reviews on subs lately, but I'm having a difficult time understanding results. I've even read through a lot of procedure and methodology articles as well.

I cannot find anybody defining the db in the graphs, or their relationship to Hz. I read something stating THX reference level is 75db, which in turn (roughly) translates to 0db on a receiver.

Is this correct?

I'll use an SVS SB12-NSD to illustrate further.

According to SVS the sub can output across 23-270Hz. However, if we look at a review, such as Audioholics I'm lead to believe differently.

If my db reference is valid, then according to the Audioholic's review I would expect the sub to produce ~18-20hz anywhere from 0db to -10db on my receiver. http://www.audioholics.com/reviews/speakers/subwoofers/sb12-nsd-subwoofer/Asb12nsdbasicresponse.jpg/image_view_fullscreen

If that's the case, why not claim the sub is able to produce a wider array of results?

Curious if I'm understanding these type of results correctly, or if I'm missing something fundamental. Appreciate any feedback.
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post #2 of 22 Old 08-24-2012, 08:22 AM
 
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Hey Superman, two things that might help without getting too complicated. Reference peaks in films for the subwoofer channel are around 115dB, and most reviews are measuring max output of the sub. Ideally you want to be in a comfort zone on those peaks, and not at the limit or worse, below the subs capabilities. Give yourself a little bit of headroom.

The level you reference on your receiver will depend greatly on your distance from the sub (most reviews measure at 1 or 2 meters), and the gain you get in your room.

If your distance from the subwoofer is 4 meters, it would be 6dB less than the 2 meter measurement.
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post #3 of 22 Old 08-24-2012, 01:15 PM
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IMHO, prolonged listening at true Reference Level is an invitation to eventual hearing loss. Several members do listen at Reference Level but they have acclimated themselves to Reference Level. There is at least one thread here on AVS, (do a search), dealing with hearing loss at really high listening levels.

From my own experience listening to music at 92 db was painfully loud.

If you value your hearing you might want to steer clear of Reference Level smile.gif
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post #4 of 22 Old 08-24-2012, 01:44 PM
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Quote:
Originally Posted by spyboy View Post

Several members do listen at Reference Level but they have acclimated themselves to Reference Level.

In other words, they're now partially deaf. smile.gif

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post #5 of 22 Old 08-24-2012, 01:51 PM
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Hearing loss is a pandemic among those who listen to their IPods at high levels. I've seen the stories on the evening news. These young people don't fully comprehend the damage being done by listening to loud music. Maybe there is a parallel with movies (at Reference Level). The same guys who are into IPods are going to be shopping for AV gear really soon. Hearing loss is growing at an alarming rate among IPod users. There must be a lesson to be learned here somewhere...
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post #6 of 22 Old 08-24-2012, 01:56 PM
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http://www.gcaudio.com/resources/howtos/loudness.html

Keep in mind most people that say they are listening at reference level are most likely (I hope) talking about peaks. Say a 2 hour movie has 15-20 minutes that hits near or slightly above 100db during peak scenes. You are well within safe limits assuming you are not watching TV at these peak levels or doing other things like working with power tools all day long.

Once you start talking 110db+ levels, I think you need to be really careful. My father worked construction his whole life with power tools (the majority of the time with little to no hearing protection) and has to wear hearing aids now. I have buddies from my military days that, in their 30's-40's, have developed noticeable hearing loss because they did not wear hearing protection as they should have when shooting weapons.

Hearing loss is no joke. Better to be safe than sorry, but clearly peaks at or near reference level for short periods of time can be safety attained.
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post #7 of 22 Old 08-24-2012, 02:05 PM
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I worked at the pleasure of Tom Ridge, a Viet Nam veteran. He was the Governor of Pennsylvania before becoming the Chief of Homeland Security. He suffered significant hearing loss due to the gun fire he was exposed to. It is ironic that Apple is the most profitable company in the USA while IPod users are suffering hearing loss.

After exposure to their IPods, the hearing loss is already there. The next generation of AV users will be able to listen at Reference Level since the damage has already been done. redface.gif
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post #8 of 22 Old 08-24-2012, 08:03 PM
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Quote:
Originally Posted by Superman07 View Post

I've been reading a lot of reviews on subs lately, but I'm having a difficult time understanding results. I've even read through a lot of procedure and methodology articles as well.
I cannot find anybody defining the db in the graphs, or their relationship to Hz. I read something stating THX reference level is 75db, which in turn (roughly) translates to 0db on a receiver.
Is this correct?
I'll use an SVS SB12-NSD to illustrate further.
According to SVS the sub can output across 23-270Hz. However, if we look at a review, such as Audioholics I'm lead to believe differently.
If my db reference is valid, then according to the Audioholic's review I would expect the sub to produce ~18-20hz anywhere from 0db to -10db on my receiver. http://www.audioholics.com/reviews/speakers/subwoofers/sb12-nsd-subwoofer/Asb12nsdbasicresponse.jpg/image_view_fullscreen
If that's the case, why not claim the sub is able to produce a wider array of results?
Curious if I'm understanding these type of results correctly, or if I'm missing something fundamental. Appreciate any feedback.

Reference level is a calibration not an spl for any particular content. To repeat, reference level is a calibration. It is used for mixing movies so that every sound in the final sound track is at a specific SPL level when played back at reference.

Here's how it works. In the digital age, the max encodable level is called 0dBFS(full scale). Everything that is not at full scale can be described as - some number of dB from full scale. Movie mixing rooms (and movie theaters, at least theoretically), are calibrated so that pink noise encoded at -20dBFS plays back at 85 dB in each speaker (surrounds are actually 82 but there are always multiples on a movie mixing stage and home calibration equal to the mains is appropriate).

It was discovered by AVR manufacturers that their customers found 85 dB too blinking loud to listen to a test noise, so they started using a different way to achieve the same thing. Using a pink noise signal encoded at -30 dBFS, home speakers are calibrated at 75 dB. It should be apparent upon reflection that these result in exactly the same calibration. A sound encoded at -40 dBFS will sound at 65 dB at reference level under either calibration approach. A sound encoded at 0dBFS would be 105 dB in the room. It's a bit confusing but you can't confuse sound pressure in a room - - dB SPL - - with the encoding levels of movies or other media.

I tend to listen to movies well below reference. If I set my master volume at -20 dB, that means that a sound encoded at -20 dBFS on disk will sound 65 dB loud in my room, versus the 85 it would be if I were at reference.

Now the last twist important for consideration of sub specs is that the LFE channel (the .1 in 7.1) actually can play louder than all the others. What happens is that after reading the digital data off the disk, the system turns it up 10 dB (so the whole LFE channel is encoded differently from the rest of the channels). Thus the LFE channel max, at reference, is 115 dB, and at my -20 dBFS master volume level, the LFE channel will max out at 95 dB.

There are "rules" for movies as to calibration so that playback can be consistent with artistic intent of the film's makers, in the calibration described above. There are no rules whatsoever that say how loud anything must be in a movie. Silent passages will be encoded as all zeroes digitally, and will be silent whether you play at reference or far below. I've seen it said that dialog runs typically somewhere around the 85 dB SPL range, but that's far far from a hard and fast rule and some movies have it significantly lower. V for Vendetta is an example of a movie with much lower than normal dialog levels.

The questionthen is whether the sub in which you are interested can play back the frequency range you want at the level you will actually use in your room. While I'd be happy to have a system that could play at reference levels to below 20 Hz without undue distortion or compression, I don't need it. And that 20 dB difference requires 100 times more power than the levels I use. At least until you throw in rqualization to correct for the equal loudness curves but I've been far too detailed and technical already
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post #9 of 22 Old 08-25-2012, 04:56 AM
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^^^^ What JHAz said.

One further tidbit. As stated, the LFE channel can deliver peaks at 115dB, and each of your other channels can deliver peaks of 105dB. Bass management (redirecting bass away from your satellites to your subwoofer) can further increase the loading on the subwoofer, increasing the theoretical maximum to 123dB for 5.1 content.
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post #10 of 22 Old 08-25-2012, 06:17 AM
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JHaz,

That is the best, most concise explanation of Reference Level I've ever seen. I have tried to explain it many times myself, and never was able to get the details into such a concise and easily understandable wording. I have bookmarked your post and will refer to it whenever this question arises again in the future. Thanks!

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post #11 of 22 Old 08-25-2012, 06:34 AM
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Quote:
Originally Posted by spyboy View Post

IMHO, prolonged listening at true Reference Level is an invitation to eventual hearing loss. Several members do listen at Reference Level but they have acclimated themselves to Reference Level. There is at least one thread here on AVS, (do a search), dealing with hearing loss at really high listening levels.
From my own experience listening to music at 92 db was painfully loud.
If you value your hearing you might want to steer clear of Reference Level smile.gif
The amount of content in virtually any movie that is at or close to Full Scale Reference Level, (FSRL), is but a small fraction of the total content. Most of the content is is -20 to -30 below FSRL. More importantly, the high SPL levels are not *sustained*, they are intermittent. OSHA has recommendations for maximum noise levels over time:
Quote:
With noise, OSHA's permissible exposure limit (PEL) is 90 dBA for all workers for an 8 hour day.
(emphasis added)
http://www.osha.gov/SLTC/noisehearingconservation/

It's highly unlikely that any movie will be significantly above 90 dB "average" levels, and most movies are around 2 hours in length. IOW, it's not likely that listening to movies at FSRL will cause hearing loss, even if you watched several movies per week at those levels, (unless of course, you are exposed to high SPL's routinely in other environments besides your HT.)

Listening to movies at FSRL is not the same as IPod listening at high levels. Due to the compression on IPods, the average, sustained levels are much higher than than the average sustained levels in an HT at FSRL. I don't even own an IPod because I can't stand the compressed sound.

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post #12 of 22 Old 08-25-2012, 07:30 AM
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I have my speakers calibrated to 85...and I listen @-10 on my receiver...so if I understand this correctly, Iam at or around the reference point that the manufactures intend?

I always thought -10 is perfect for reference sound for me and only change that volumne on occasion, cause some dialog in movies are to loud or not loud enough...but -10 is probably 80 % of the time perfect for me.
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post #13 of 22 Old 08-25-2012, 08:15 AM
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I've played bass guitar since I was 13 years old, at which age I was hired as a session bassist to record a CW single. By the age of 18, I played football stadium, one of which used the same sound folks who did Woodstock 3 years earlier. I worked on Cerwin Vega's Boogie Barge on the 3 rivers in Pittsburgh that was so loud it changed your heartbeat.

I've been into surround since ProLogic and upgraded to AC-3 when it came out and I'm not timid about playback levels. What I've found is that, generally speaking, movie soundtracks are far less a danger to hearing loss than modern music, which is so compressed that you get a constant high level of SPL.

Have a look at any of the peaks-to-average graphs done of movie soundtracks by Maxmercy in the Master List thread and you'll see a 30dB difference. Some modern discs have been compressed to a 2 or 3dB difference. No dynamics, all loud level.

Honestly, being a city boy most of my life, there is background noise 24/7/365, and it gets louder every year. The mild case of tinnitus I suffer in my old age is completely drowned out by city ambience. Just riding in a car with a window cracked at 70 mph on any highway in the US is worse than watching a movie at reference level. Chain saws, leaf blowers, commercial mowers, chipper/shredders, fire trucks, ambulances, police cars, subways, trains, planes and automobiles... it's a loud world we live in. Way louder and far longer exposure times than a movie.

It's unfortunately too dangerous to walk, drive or ride a bicycle with ear protection, but, if you're worried about 90 minutes of a soundtrack at reference levels, most of which only have a fraction of levels at the huge numbers that are always quoted here, and almost never at the 120+dB numbers claimed, then you should be doubly worried about everyday life in the big city.

Bottom line for me is that music discs are far, far more a danger to hearing than any movie because of the ridiculous compression schemes that lead to ever louder and louder mixes from a peak-to-average perspective.

There's no chance I'm watching a movie at -20dB, which puts the conversations below real life conversations and that's IF you're sitting at the primary listening position, directly on axis. Heck, a telephone dial tone is 80dB. A lawn mower at 3' is 107dB, which OSHA says you can endure without hearing loss for an hour a day. And like OSHA, all noise ordinances are 'A' weighted, which means the subwoofers (which provide the lion's share of the 115dB number) are irrelevant.

A 12 gauge shotgun blast is 165dB. That's 32,000 times louder than any HT system can reproduce accurately. The closer to reality, the better, IMO. I don't advocate ridiculous listening levels and I certainly have never been a fan of headphones (never owned a pair in my life), but movies haven't adversely affected my hearing at all and music, live and discs, most definitely have.
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post #14 of 22 Old 08-25-2012, 08:23 AM
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Quote:
Originally Posted by mrcoop View Post

I have my speakers calibrated to 85...and I listen @-10 on my receiver...so if I understand this correctly, Iam at or around the reference point that the manufactures intend?
I always thought -10 is perfect for reference sound for me and only change that volumne on occasion, cause some dialog in movies are to loud or not loud enough...but -10 is probably 80 % of the time perfect for me.
That depends on the test signal you're using for calibration. If it's a -20 test signal, and you set the output to 85 dB, then your MVC is at RL when it is set to "0" and you're listening 10 dB below RL. If you used a -30 dB test signal and you set the levels to 85 dB, you're 10 dB "hot" and then a -10 MVC setting is Full Scale RL.

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post #15 of 22 Old 08-25-2012, 08:42 AM
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How many threads do we have to have about reference causing hearing damage? Most of this nonsense comes from people who tries reference and their speakers and subs clip and distort so much they claim it to be too loud. I agree 100% with Bosso and the rest. I built my room for all movies to play at Reference and I have been watching reference for 7 years straight, every movie, demos, etc... I have an audiologist in my office and I can hear to 18khz and I am 41. The best thing about HT is one can control their own volume and pause to go to the bathroom. I just want a better than IMAX experience so reference it needs to be!

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post #16 of 22 Old 08-25-2012, 10:50 AM
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I guess the reason for hearing loss due to IPOD (played at high volume levels) is the proximity of the headphones to the ears, irrespective of whether I play compressed music or loss less format. No?
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post #17 of 22 Old 08-25-2012, 06:56 PM
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Quote:
Originally Posted by craig john View Post

That depends on the test signal you're using for calibration. If it's a -20 test signal, and you set the output to 85 dB, then your MVC is at RL when it is set to "0" and you're listening 10 dB below RL. If you used a -30 dB test signal and you set the levels to 85 dB, you're 10 dB "hot" and then a -10 MVC setting is Full Scale RL.
Craig

How do you know what test signal is sent?
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post #18 of 22 Old 08-26-2012, 10:00 AM
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Quote:
Originally Posted by bossobass View Post

I've played bass guitar since I was 13 years old, at which age I was hired as a session bassist to record a CW single. By the age of 18, I played football stadium, one of which used the same sound folks who did Woodstock 3 years earlier. I worked on Cerwin Vega's Boogie Barge on the 3 rivers in Pittsburgh that was so loud it changed your heartbeat.
I've been into surround since ProLogic and upgraded to AC-3 when it came out and I'm not timid about playback levels. What I've found is that, generally speaking, movie soundtracks are far less a danger to hearing loss than modern music, which is so compressed that you get a constant high level of SPL.
Have a look at any of the peaks-to-average graphs done of movie soundtracks by Maxmercy in the Master List thread and you'll see a 30dB difference. Some modern discs have been compressed to a 2 or 3dB difference. No dynamics, all loud level.
Honestly, being a city boy most of my life, there is background noise 24/7/365, and it gets louder every year. The mild case of tinnitus I suffer in my old age is completely drowned out by city ambience. Just riding in a car with a window cracked at 70 mph on any highway in the US is worse than watching a movie at reference level. Chain saws, leaf blowers, commercial mowers, chipper/shredders, fire trucks, ambulances, police cars, subways, trains, planes and automobiles... it's a loud world we live in. Way louder and far longer exposure times than a movie.
It's unfortunately too dangerous to walk, drive or ride a bicycle with ear protection, but, if you're worried about 90 minutes of a soundtrack at reference levels, most of which only have a fraction of levels at the huge numbers that are always quoted here, and almost never at the 120+dB numbers claimed, then you should be doubly worried about everyday life in the big city.
Bottom line for me is that music discs are far, far more a danger to hearing than any movie because of the ridiculous compression schemes that lead to ever louder and louder mixes from a peak-to-average perspective.
There's no chance I'm watching a movie at -20dB, which puts the conversations below real life conversations and that's IF you're sitting at the primary listening position, directly on axis. Heck, a telephone dial tone is 80dB. A lawn mower at 3' is 107dB, which OSHA says you can endure without hearing loss for an hour a day. And like OSHA, all noise ordinances are 'A' weighted, which means the subwoofers (which provide the lion's share of the 115dB number) are irrelevant.
A 12 gauge shotgun blast is 165dB. That's 32,000 times louder than any HT system can reproduce accurately. The closer to reality, the better, IMO. I don't advocate ridiculous listening levels and I certainly have never been a fan of headphones (never owned a pair in my life), but movies haven't adversely affected my hearing at all and music, live and discs, most definitely have.

I had this type of experience at the Tower Theater in Philadelphia at a Tracy Chapman concert. I was in about the 3 third row right in front of a massive bank of (pro) subwooferss. This kind of experience is pretty much hard to forget.
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post #19 of 22 Old 08-27-2012, 04:47 AM - Thread Starter
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While I appreciate the PSAs on high volumes and hearing loss, I'm not sure the discussion addresses my original questions.

For instance is there a fundamental definition of reference level, and is that implemented or represented consistently across AV manufacturers?

Also, still not understanding bass charts and relationship of db to Hz.
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post #20 of 22 Old 08-27-2012, 09:47 AM
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Quote:
Originally Posted by JHaz 
Movie mixing rooms (and movie theaters, at least theoretically), are calibrated so that pink noise encoded at -20dBFS plays back at 85 dB in each speaker (surrounds are actually 82 but there are always multiples on a movie mixing stage and home calibration equal to the mains is appropriate).
Great explanation of Reference Level. However, some of what I have read says that studios use 83 dB as Reference Level. The Disney World of Wonder calibration disc uses 83 dB as the Reference Level and Richard Casey, its author, has stated that studios uses 83 dB as Reference Level.

There are other references to using 83 dB as Reference Level. Here are a couple.

The Magic of "83" with Film Mixes

Studio Tanning: Calibrated Mixing

There are also a bunch of threads at gearslutz.com about calibrating to 83 dB. There is a thread about 83 dB vs 85 dB that is of interest.

Genelec's website says that Reference Level is 85 DB, and goes on to say that calibrating with a 1/3 octave RTA and broadband pink noise you should use 85 dB, but when using filtered pink noise and an SPL meter you should use 83 dB.
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post #21 of 22 Old 08-27-2012, 11:12 AM
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Quote:
Originally Posted by desertdome View Post

Great explanation of Reference Level. However, some of what I have read says that studios use 83 dB as Reference Level. The Disney World of Wonder calibration disc uses 83 dB as the Reference Level and Richard Casey, its author, has stated that studios uses 83 dB as Reference Level.
There are other references to using 83 dB as Reference Level. Here are a couple.
The Magic of "83" with Film Mixes
Studio Tanning: Calibrated Mixing
There are also a bunch of threads at gearslutz.com about calibrating to 83 dB. There is a thread about 83 dB vs 85 dB that is of interest.
Genelec's website says that Reference Level is 85 DB, and goes on to say that calibrating with a 1/3 octave RTA and broadband pink noise you should use 85 dB, but when using filtered pink noise and an SPL meter you should use 83 dB.

I nteresting. I didn't review them all, but am familiar with Bob Katz's superb work in attempting to reclaim life in music recordings. His reference to 83 dB in movies is "This is an incredible testament to the effectiveness of the 83 dB SPL reference standard proposed by Dolby's Ioan Allen in the mid-70's, originally calibrated to a level of 0 VU for use with analog magnetic film." IDK how 0 VU on magnetic film relates to -20dBFS digital. At any rate, I've never seen FilmMixer or others reference a different standard (except for surrounds) and AFAIK all those megabuck mixing houses calibrate to 85dB with a -20dBFS bandwidth limited pink noise source (with, IIRC, a 6 dB crest factor - differently shaped noise could call for a different in room SPL).

Anyway if I'm within 2 dB of actual reference, I'm not too worried about the difference . . .
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post #22 of 22 Old 08-27-2012, 11:13 AM
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Quote:
Originally Posted by JHAz View Post

I nteresting. I didn't review them all, but am familiar with Bob Katz's superb work in attempting to reclaim life in music recordings. His reference to 83 dB in movies is "This is an incredible testament to the effectiveness of the 83 dB SPL reference standard proposed by Dolby's Ioan Allen in the mid-70's, originally calibrated to a level of 0 VU for use with analog magnetic film." IDK how 0 VU on magnetic film relates to -20dBFS digital. At any rate, I've never seen FilmMixer or others reference a different standard (except for surrounds) and AFAIK all those megabuck mixing houses calibrate to 85dB with a -20dBFS bandwidth limited pink noise source (with, IIRC, a 6 dB crest factor - differently shaped noise could call for a different in room SPL).
Anyway if I'm within 2 dB of actual reference, I'm not too worried about the difference . . .

And thanks for the kind words. If my brain will retain the query, I'll dig into your other refs tonight because it's quite interesting stuff (to me).
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