THX Ultra2 Reference Level Calibration, the Good News and Bad News - Page 2 - AVS Forum
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post #31 of 53 Old 12-20-2013, 03:37 PM
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Quote:
Originally Posted by BassThatHz View Post

Check it out. I just made the file. Good luck trying to pass it wink.gif

If nothing else... it will help to tell the difference between -20db pinknoise and 0db burst power. eek.gifbiggrin.gif



and the raw sound file (if you don't like youtube quality):
ReferenceLevelPlaybackOptimizer.ogg 3957k .zip file

I decided not to make it a DVD iso, too much effort and too big an upload.

That's awesome...... So awesome! Can I play this using apple airplay and not lose accuracy?

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post #32 of 53 Old 12-20-2013, 04:09 PM
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Quote:
Originally Posted by LTD02 View Post

"How do you know what the THX standard is?"

for a long time, thx has been coy about what exactly its certification means...because of course if consumers knew that 85/105/115 was the standard, then everybody with 85/105/115 could say that is where they are without paying thx any money.

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

Yes that is sort of what i was thinking. THX is a secret standard, so how does one know how to meet it other than to buy a complete THX certified setup including both processing, amplification, speakers and subs. Even then i have a feeling you might not meet the insane SPL requirements often quoted in relation to "reference". Especially regarding the subwoofers.

EDIT: On the other hand. If you look at subwoofers that are in fact certified THX-ultra2, it appears that the SPL requirement might not be all that hart to meet. For instance the Jamo D600 sub is a 15" sealed box sub with a good, bun not exactly impressive amp. If that is good enough for ultra2 then how can the spec be 115db+. The Jamo sub certainly wont ever go there unless in a multi sub setup.
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post #33 of 53 Old 12-20-2013, 05:14 PM
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Here is some good reading - http://www.hometheaterhifi.com/volume_13_1/feature-article-thx-1-2006-part-4.html

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post #34 of 53 Old 12-20-2013, 05:30 PM
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Is that a 13B-RE that I see? No rear cylinder to be bothering thee! :-)

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post #35 of 53 Old 12-20-2013, 06:20 PM - Thread Starter
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I just passed step 3 successfully, here's a video to prove it.
To be honest, the first time I subjected my electronics to this test, I failed it (5db too hot), but I adjusted my bass level down 5db and now I pass it, but just BARELY My bass is a bit on the weak side apparently. eek.gif

I created a "THX" setting in my DCX for this, I'll run with it like this for a while just to see how it goes.

But there is NO WAY I'm doing step 4 though!!!! eek.gif

Quote:
Originally Posted by LTD02 View Post

"How do you know what the THX standard is?"
for a long time, thx has been coy about what exactly its certification means...because of course if consumers knew that 85/105/115 was the standard, then everybody with 85/105/115 could say that is where they are without paying thx any money.
http://www.thx.com/consumer/thx-technology/thx-reference-level/

Yeah that's it right there, quote: "Experience Studio Clarity: -> 85dB SPL with 20dB of headroom."

I just took that and ran with it, that's the closest thing we have to go by, at least....
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post #36 of 53 Old 12-20-2013, 07:11 PM - Thread Starter
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That's awesome...... So awesome! Can I play this using apple airplay and not lose accuracy?
No idea... it might be ok; I mean, it will do "something" biggrin.gif
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post #37 of 53 Old 12-20-2013, 07:33 PM
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"If that is good enough for ultra2 then how can the spec be 115db+."

because they are fuzzy with respect to the -6db point.

mksound got thx cert with its dual 12" sealed box.



not exactly a "bottom feeder"



iirc, the idea was that in a medium room, there would be pressure vessel gain sufficient when combined with that natural response to get usable output to 20hz.

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post #38 of 53 Old 12-20-2013, 07:42 PM
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assuming dual 12" drivers and about 400 watts power, that gets you to 115db at 50hz in 2 pi space. not really remarkable, but hey its 115db in some sense and with room gain that probably translates fairly closely to listening position. and with pressure vessel gain, the -6db point can be extended from about 30hz down to about 20hz roughly.

the problem thx faced back in the day and still faces to an extent today is that to get to "movie theater" sound levels in the bass requires more gear than the typical person will ever want in the room with their tv.

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post #39 of 53 Old 12-20-2013, 08:21 PM - Thread Starter
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Quote:
Originally Posted by splotten View Post


Yes that is sort of what i was thinking. THX is a secret standard, so how does one know how to meet it other than to buy a complete THX certified setup including both processing, amplification, speakers and subs. Even then i have a feeling you might not meet the insane SPL requirements often quoted in relation to "reference". Especially regarding the subwoofers.

EDIT: On the other hand. If you look at subwoofers that are in fact certified THX-ultra2, it appears that the SPL requirement might not be all that hart to meet. For instance the Jamo D600 sub is a 15" sealed box sub with a good, bun not exactly impressive amp. If that is good enough for ultra2 then how can the spec be 115db+. The Jamo sub certainly wont ever go there unless in a multi sub setup.

It says in right the jamo manual, for example:




If that's all it takes to get their "bling" sticker then I definitely pass it, and so do many others around here; but I wonder if that is nothing more than THX just being "nice" to the manufacturers;
sure I'll give you a sticker if you give us money, right? haha smile.gif We all know how that game goes.
Maybe THX is getting loose and soft so that more than 1 product, costing zillions, makes their cert list wink.gif Your guess is as good as mine...
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post #40 of 53 Old 12-21-2013, 01:36 AM
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with 2 x 15 inch drivers at 700 watts each sealed, that's about 115db at 30hz before room gain / pressure vessel gain (106db @20hz) and only requires about 15mm or so of excursion.

so, i guess that is thx ultra 2. :-)

i suppose thx would need a new category for the...martysub...and its 118db at 20hz. lolz.

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post #41 of 53 Old 12-21-2013, 04:26 AM
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I always watch at reference levels, I never really bothered with the low end spec as a goal. This is the loudest I listen though.
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post #42 of 53 Old 12-21-2013, 05:26 AM
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while not thx, here is what dolby is specifying for atmos. i can only assume that dolby atmost meets thx spec too. :-)



which raises an interesting dilemma...an 80hz crossover point neuters the headroom in the lfe from 80-120hz, where i suppose a lot of the band in explosions comes into play.




Dolby-Atmos-Cinema-Technical-Guidelines.pdf 1507k .pdf file
Attached Files
File Type: pdf Dolby-Atmos-Cinema-Technical-Guidelines.pdf (1.47 MB, 3 views)

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post #43 of 53 Old 12-21-2013, 05:31 AM
 
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Quote:
Originally Posted by LTD02 View Post

"If that is good enough for ultra2 then how can the spec be 115db+."

because they are fuzzy with respect to the -6db point.

mksound got thx cert with its dual 12" sealed box.



not exactly a "bottom feeder"



iirc, the idea was that in a medium room, there would be pressure vessel gain sufficient when combined with that natural response to get usable output to 20hz.

I actually owned an M&K MX sub for a while. That thing would get crazy loud with tons of output, and it beat the socks off my MFW-15!
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post #44 of 53 Old 12-21-2013, 05:38 AM
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I used to own many M&K subs. They were awesome THX subs but it took too many to get any real output down low. They were not cheap. I had dual MX-5000's at one time.
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post #45 of 53 Old 12-21-2013, 05:58 AM
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mk, have you got a nearfield sweep of the ib318's? just a raw sweep, no eq or anything...

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post #46 of 53 Old 12-21-2013, 06:33 AM
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Not yet, I have a raw sweep at the LP and have not EQ'd my subs. I have a bassis on the way and once I get it I will measure nearfield and then add the L/T accordingly and then run a LP measurement.
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post #47 of 53 Old 12-21-2013, 01:47 PM
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What exactly is the bassis? Basically a sub EQ with ability to add an LT?

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post #48 of 53 Old 12-21-2013, 02:30 PM
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Marchand bassis which allows boost below 10hz and rolls off at 2-3 hz. Analog not digital. Getting it from gpmbc.
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post #49 of 53 Old 12-21-2013, 02:44 PM
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Cool thanks.

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post #50 of 53 Old 12-21-2013, 03:38 PM
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I'll try to touch on a couple of themes in this thread that I think I can help clarify. Too many to try to quote...

1) The THX specification has changed over time. As mentioned, lots of good info in the HometheaterHiFi article. Before DD discrete audio, the subwoofer only needed to meet 105dB @ 30Hz. Presumably, there's also a distortion component to this spec, but I've never seen it published. Some time after the arrival of DD with it's +10dB boost in the LFE decoder, the goal posts were moved to 115dB. Either at the same time, or later, the f3 point was moved to 20Hz. As someone mentioned, THX does allow for some "standard" room provided gain. And, as shown in the Jamo manual, many subwoofers require multiples to meet the spec, especially after the 115/20Hz change. I remember back in the day (early/mid '90s), McIntosh's THX sub actually had a factory published anechoic f3 of 37Hz...THX has always considered room gain in the equation.

2) Bass, when you did your first video showing -20 for the test signal, is the computer connected via digital output to your receiver/prepro? If you're using analog outputs, you've still got the Windows volume control and possibly another gain stage or two between REW and the decoder. This could definitely explain why you're just barely making it with the wattage listed. There are probably other sources of test tracks, but Soho54 created a downloadable DVD ISO many moons ago that contained individual DD 5.1 channels of white/pink noise, including LFE along with individual sine waves down to 10Hz IIRC. The link is probably still in the forum archives, but I don't know if the ISO is still being hosted at the link.

-Brent
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post #51 of 53 Old 12-21-2013, 10:26 PM - Thread Starter
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Has anyone tried to pass the test with my file yet? It would only really be possible to know, if you have pro-gear with clip light indicators on all channels like I do. (Even better if it expresses the input/output levels in a db-scale.)

20db is a 100-fold increase in power level beyond the pinknoise level. That's why it takes so much power to do it unclipped; it's not an easy test at all (even just electronically.)

Subs like those Jamo's etc etc are tested at 3ft by THX no doubt.
But MY test requires that it be done at the main LP, just to make it extra challenging upon you, and because, NOBODY watches a movie at 3ft (or at least I hope nobody does.) BassThatHz-Ultra2 Certification, hehe smile.gif

My gain structure is good and plentiful (I can saturate all inputs and outputs if I wanted to); However, I should burn a test disc of my own to ensure that the DD/DTS decoders are also functioning correctly in 7.1 (because you never know until you know).
I was running this test in 2-channel mode. (I'm not really prepared to apply it to all 8 channels at this time, but I will, when the time is right. wink.gif )
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post #52 of 53 Old 12-22-2013, 08:38 AM
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THX reference is at the seats.
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post #53 of 53 Old 12-24-2013, 02:41 PM
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Quote:
Originally Posted by BassThatHz View Post

Has anyone tried to pass the test with my file yet? It would only really be possible to know, if you have pro-gear with clip light indicators on all channels like I do. (Even better if it expresses the input/output levels in a db-scale.)

20db is a 100-fold increase in power level beyond the pinknoise level. That's why it takes so much power to do it unclipped; it's not an easy test at all (even just electronically.)

Subs like those Jamo's etc etc are tested at 3ft by THX no doubt.
But MY test requires that it be done at the main LP, just to make it extra challenging upon you, and because, NOBODY watches a movie at 3ft (or at least I hope nobody does.) BassThatHz-Ultra2 Certification, hehe smile.gif

My gain structure is good and plentiful (I can saturate all inputs and outputs if I wanted to); However, I should burn a test disc of my own to ensure that the DD/DTS decoders are also functioning correctly in 7.1 (because you never know until you know).
I was running this test in 2-channel mode. (I'm not really prepared to apply it to all 8 channels at this time, but I will, when the time is right. wink.gif )

I plan on seeing where Im at, but I will be nowhere near the headroom requirements. Waiting on the mini dsp 2x8 to show up.

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