Sub calibration + 4dB or not ?

Discussion in 'Archived Threads 2001-2004' started by Frank Doorhof, Jun 28, 2001.

  1. Frank Doorhof

    Frank Doorhof Stunt Coordinator

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    Hi,
    Just when you think you have done everything right you read something on the net and you're all confused
    The problem is, the real calibration of LFE.
    I know about placement and so on. To be honest I'm not even a beginner, but still I don't seem to get an explanation to my question.
    The question is very simple.
    Normaly I calibrated (with RTA) on exactly 85dB including subwoofer. No I keep reading about that the sub MUST officially be 4dB higher calibrated.
    Is this true ?
    And does it also goes for DTS, because I know DD has a headroom of + 10dB, but I thought this was compensated for on the test tones on AVIA.
    Hope someone can shine his/her licht on this.
    The articles I read are from professionals and not the major I know what to do blokes. But they all seem to forget to give the reason why, if so............
    Please help [​IMG].
    Greetings from Holland,
    Frank
     
  2. Steve_D

    Steve_D Second Unit

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    First of all, you don't HAVE to do anything.
    For reference, you said you use a RTA with Avia? Do you mean C weighted SPL with Avia?
    VE and Avia have compensated in the recording level the 10 db sub so you set all tracks to the same SPL. Read the FAQ at videoessentials.com, here's a quote:
    "
    Confusion has come up about setting this level because the LFE channel in the Dolby Digital 5.1 system is actually recorded 10 dB below the levels of the other five channels of audio. This is done to increase the 'headroom' available to large signals in the LFE track. Your Dolby processor will take care of this level offset for you automatically, it is not something you should be concerned with during system calibration.
    "
    Remember if you are using the RS meter that the lower frequencies aren't the most accurate. I use an average of +2 DB to the reading for the band limited noise. Therefore, for absolute correctness, an argument can be made for a reading of 83DB on the meter, versus 85 for the other channels. Having said all of that, I have my sub set at 87 db (for movies only!) versus 85 for the others, which really means my sub is +4 db higher than reference. I arrived at this conclusion completely separately from the page that says +4 db, and realize its not totally correct, its just my preference.
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  3. Julian Data

    Julian Data Second Unit

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    Frank,
    Where exactly are you reading that "+4dB" higher for the LFE? The standard for REF is 75dB. You can go higher than this but it usuallly based on preference for "any" channel, it just depends on one's tastes.
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  4. Frank Doorhof

    Frank Doorhof Stunt Coordinator

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    http://www.surroundassociates.com/spkrcal.html I believe there is a C weighting in the software (soundtechnologies), I'm not sure if it's also called that way, but I know the testpattern from my mains (I know the guys who build them, BIG advantage) and my RTA gives the same response as the lab's RTA so it should be ok. And by the way if I check calibration later on with a dB meter, it checks out (I always crosscheck [​IMG] call me paranoid)
    I believe however that in this article it's taking the assumption that you use a pink noise scheme on the TAPE, and therefore has to compensate. I was OK with that untill I found this +4dB popping up all over on sites even on the Radioshack site. It's always that + 4dB value.
    That's the reason I was wondering, I tried it with +4dB and I still liked my bass, it's a bit more there but not enoying. Because I also do calibrations for customers I want to do it the right way, but that is ............?
    I will stick however to the same SPL as the mains (for the time being, untill it's exactly clear).
    I don't think it's a matter of liking, it's a matter what's the RULE and than color it as you like. I will dive into that quote from VE and keep that as my rule of thumb for the moment. But still it's intresting......
    Greetings,
    Frank
     
  5. Julian Data

    Julian Data Second Unit

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    In that case, 75dB is the rule, anything over is "preference.
    I think majority of these sites that state anything over 75dB is surely by the trend of what ppl are doing to satisfy their tastes, IMHO.
    ... "monkey see, monkey do".
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  6. Greg Monfort

    Greg Monfort Supporting Actor

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    Just to muddy the waters a little bit more, back when I still had a HT, I set levels per DD's mixing manual http://www.dolby.com/tech/L.mn.0002.5.1Guide.s.pdf which specs 85dB for the L-C-R and each surround when using a RTA, with various ways of doing the LFE depending on the bass management, but the net result being a 10dB headroom WRT the other channels. According to it, 75dB is for broadcast TV playback.
    DD is compressed to a nominal 20dB of dynamic headroom in the five channels, and specs a peak of 105dB/listening position, which means an 85dB average level, so I guess I don't understand why 75dB is the 'rule'.
    GM
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    Loud is beautiful, if it's clean
     
  7. Tom Vodhanel

    Tom Vodhanel Cinematographer

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    the 4dB higher thing originates with the SPL meter vs. RTA issue.
    Suppose you're using a RTA with whatever source material...and it reads the same for the mains as the sub in 1/3 octave bandwidths.Then...if you're using a SPL meter...it will read (about)4dB lower on the woof calibration because of the bandwidths involved.
    supposedly,VE and AVIA have already accounted for this in their recordings. I checked through all of them a while back...and although i have pages of notes on it buried somwhere...my final conclusion was that using the recommendations given by VE and AVIA worked fine. But there's still the typical 2-3dB rolloff for the RS SPL meter to factor in on the woof tones...
    TV
     
  8. Frank Doorhof

    Frank Doorhof Stunt Coordinator

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    I already had taken in account that AVIA and VE had done a compensation, otherwise it should be noted on the instructions.
    And I believe you are right about the RTA, when calibrating with the RTA I DO get different readings only the other way arround, on the dB meter it reads a bit hotter than 85dB between 1-3 dB (I have no slow [​IMG] on the meter so it jumps arround).
    I switched to RTA because in a day to day basis it's just so much easier than a dB meter and the customers see what I'm doing so are less moved to change everything when I'm gone resulting a better calibration [​IMG]
    I will look into that Dolby document.
    Nice to have so much confussion [​IMG]
    Greetings from Holland,
    Frank
     
  9. Tom Vodhanel

    Tom Vodhanel Cinematographer

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    >>>And I believe you are right about the RTA, when calibrating with the RTA I DO get different readings only the other way arround, on the dB meter it reads a bit hotter than 85dB between 1-3 dB (I have no slow on the meter so it jumps arround).
     
  10. Tom Damico

    Tom Damico Auditioning

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    A note from a novice:
    I really enjoy reading the highly technical information in this site as well as AVS. It stretches me and that is always good. I can't say I follow all the technical aspects of this subject, but I have built a HT system primarily with what I read here, what my gut tells me, and then experiment. I was at the SVS subwoofer site the other day looking at their subs, and it seemed to me that they reccomended that the sub be set at a higher rating than the rest of the system. Now I do have a SPL meter and have tried to keep the sound calibrated to the best of my ability. So when I read the SVS info, I recalibrated as they suggested. I lowered the output of the LFE channel on my receiver to a minus number (-6) then I calibrated with the SPL all speaker to 75 and then the sub to 82 (VE). Please forgive me, I can not argue this from a technical point of view, but I will say that my systems has never sounded better. The bass is not overpowering, but I seem to feel it, no, I know I feel it more in places that I didn't before. I have built my system and upgraded it a few times over the last year or so. My equipment isn't the greatest, but I think its good enough to judge. Yamaha 2095 reciever, Infinity Overture 2 mains, HPS Center, RS3's effects, and an HPS1000 sub.
    TomD
     
  11. Frank Doorhof

    Frank Doorhof Stunt Coordinator

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    It's all a matter of taste.
    I like the subwoofer at the calibrated settings (wooden floor [​IMG].
    By the way being on the subject, I found out something else shocking.
    This week I have fiddled arround with some pre-amps, and I found out something very strange (please check this).
    Normally you calibrate a system on 75dB including Subwoofer, this SHOULD be ok for all sources.
    But when using Platinum DVD you can also have a DTS calibration set (test tones, including sub/LFE). When all is calibrated at 75dB with the DD set, and you play the DTS set the subwoofer will be + 7dB louder !
    I found only ONE preamp the GTX-1 (Cinematrix Taurus) which corrected this by playing all front channels also 7dB louder making a perfect in balance calibration.
    ALL the others did not.
    Including Myryad MDP-500 and the EAD Ovation (however the last one has memories so should not be a problem).
    Is this know with you guys ?
    And do you use a macro on for example the Pronto when lisiting to DTS ? (I used one for DTS music -10dB).
    The reason probarbly why I did not notice this before is because in our custom home theater setups we always use the GTX-1 (best bang for the buck in my opinion). Only now with DPL-II DVD-Audio etc. we were looking into other pre-amps, so only now did I notice this.
    It's also thanks to platinum with a DD & DTS test track, this should be added to AVIA.
    Your opinions please,
    Greetings from Holland,
    Frank
     
  12. Steve_D

    Steve_D Second Unit

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    Frank,
    Actually, when the DTS v Dolby digital debates were raging, someone mentioned if they crank there sub up for Dolby Digital it sounded the same as DTS. A few people tested this and found the DTS did in fact have higher sub output all other factors (equipment, source, etc..) equal. This is another reason I don't feel so bad about stting my DD up a couple of DB....I figure I'm getting some of the DTS effect.
    I would bet many people who feel DTS is superior would not feel so strongly if they all had the ability to calibrate DTS....
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  13. Frank Doorhof

    Frank Doorhof Stunt Coordinator

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    Sorry but I have to disagree with that.
    When I tested the Myryad MDP-500 I tried to listen to Dinosaur (disney) at DD (calibrated with sub at 75dB) and then switched to DTS (without touching the LFE volume) man did I hate DTS, the subwoofer was jumping arround in my room (could ride a rodeo on it [​IMG]) it was WAY too loud.
    When recalibrating to 75dB on DTS the track was in balance but I still liked the DTS track over the DD.
    My opinion is that there are a lot of pre-amps/receivers out there which uses the same trick as the Cinematrix. When calibrating at DD the RTA/SPL meter reads out 75dB for all channels including subwoofer, when reading out DTS the RTA/SPL meter reads out 82dB for the channels and 82dB for the subwoofer (so all channels are raised 7dB except the subwoofer).
    On the subject on liking DTS vs DD.
    For me the battle is clear, DTS all the way (with all channels calibrated correctly) and this lies not only in the bass section. DTS "breaths" more and sounds more defined. Although DD has come a long way. For example listen to the beautifull DD track on FREQUENTIE its gorgues.
    Greetings,
    Frank Doorhof
     
  14. Steve_D

    Steve_D Second Unit

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    I didn't say there was no difference. DTS's superior bitrate should allow for better sound. I just suggest that the "big difference" many people are hearing may actually be a higher LFE level, which many people prefer and think of as "better". Is this just a US thing?
    Anyway, I'm not quite as critical on Movie Sound tracks as I am in Stereo, so maybe what to some is a big difference to me is not. Of course, this happens all the time in this hobby of ours.
    Funny you mentioned Dinosaur. Here's a post I have active on the audio:
    http://www.hometheaterforum.com/uub/.../027767.html#7
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  15. Don O'Brien

    Don O'Brien Stunt Coordinator

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    I realize the topic has diverged and frank has received an excellent answer to his question from B Florian of Secrets on AVS. The big change in volume is usually due to the presence of dialnorm on the DD presentation of the soundtrack, while there is no such metadata present in the DTS sound track. Being that most soundtracks are created with the encoder set to -27db (the default on the present decoder), this will result in an average of a 4db drop in volume. If the Dolby encoder was set to -31, and the identical original source material was used there should be little change in volume when changing from DTS to DD (unless they purposely juiced the LFE track).
    When speaking of what dbSPL level to use to determine an accurate reference point it is important to know what level signal was recorded at. The AVIA disks tones appeared to recorded at -20dbfs, while the VE tones appear to be recorded at -30dbfs. Thus 85dbSPL is correct for use with AVIA, while 75dbSPL is correct for VE. Interestingly, 75dbSPL is the the sound pressure used by the internal tone generators of THX Ultra processors, which by default sets the system volume to the reference level during calibration.
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