Stupid ? what does reference level do.

Discussion in 'Archived Threads 2001-2004' started by Tan_U, Mar 19, 2002.

  1. Tan_U

    Tan_U Stunt Coordinator

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    I know this is stupid but what does reference level do. I think it means setting all your speakers at the same volume.... right? why would one want to by a SPL just to set his speakers at the same volume? what's the benefit.
     
  2. Paul Clarke

    Paul Clarke Supporting Actor

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    It determines the peak levels you will encounter during the viewing/listening experience. Video Essentials uses the 75dB I believe and AVIA uses 85dB. Or is that backwards? This is simply the reference level at which speaker output is matched throughout the system. Your own listening levels will most likely be lower although I find 75dB to be very tolerable.

    It also helps to determine any problems in the Pro-Logic or Dolby Digital output. Without full adjustability of all speaker channels in the receiver or pre-amp there can be uneven output. Some lower level or older receivers may not allow for Front L-R level adjustment... only balance... but you would be amazed how many of them would benefit from it.
     
  3. John Kotches

    John Kotches Cinematographer

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    Tan:
    There are two aspects to this question.
    1) The value of calibrating speakers.
    You use an SPL meter to get all speaker levels equal so that no one speaker is too loud relative to the others. This prevents the louder speaker from obscuring details from the other speakers (a psychoacoustic phenomenon.
    Our ears are notoriously bad at determining levels of SPL (aka volume) -- they are much, much better at determining changes in SPL. Using your ears is almost certainly going to have substantial variations. Typical is to set the volumes on the surrounds and sub too loud. Then when you listen, the fonts and CC are overwhelmed.
    Using an SPL straightens these issues out.
    2) What is reference level.
    For main speakers it is a maximum of 105dB SPL and 115dB SPL for the LFE channel.
    When calibrating, every product I've worked with have calibration tones at -30dB SPL below reference level for main speakers and -40dB SPL below reference level for the subwoofer. This means that all speakers reproduce 75dB as recorded by an SPL meter.
    However, AVIA uses the professional standards of -20dB SPL, so all speakers calibrate to 85dB SPL.
    During playback, reference level is achieved differently based on the product itself. For receivers (or preamp/processors) with levels listed in dB (vs. reference) 0.0dB gets you reference level. Many receivers use this method, but not all.
    Others might put the string REF up for reference level.
    Hope this helped.
    Regards,
     
  4. Tan_U

    Tan_U Stunt Coordinator

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    Yes that pretty much answered my question, thank you.

    Now to go look for a the Radio shack manual SPL meter, it's getting harder and harder to find.
     
  5. John Kotches

    John Kotches Cinematographer

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    Tan,

    Yes, but even the digital meter is better than attempting to get the settings dialed in 'by ear'.

    Regards,
     
  6. Kenny Booth

    Kenny Booth Stunt Coordinator

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    If I use an Avia test disk and a Denon 2801 AVR where should I set my amp volumn control to achieve the 85db?
     
  7. ScottAndrew

    ScottAndrew Stunt Coordinator

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    If I calibrate my speakers to 75dB at the listening position using Video Essentials and the volume on my receiver is at -27dB, does that mean that reference level at the listening position would be around +3d, and that -27dB is 30dB below reference?

    Thanks,

    Scott
     
  8. Vin

    Vin Supporting Actor

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    Kenny, read Vince Maskeeper's excellent explanation of the calibration procedure here.
    Vin
     
  9. ScottAndrew

    ScottAndrew Stunt Coordinator

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    That's interesting, but not entirely what I expected. The article indicates that whatever volume level my receiver was at when I calibrated to 75dB using the VE test tones, that is reference level.

    I have always read that reference level was extremely loud. While I definitely find it too loud to watch most films, it's not as deafening as I expected. And there are many dialogue-driven movies that are hard to hear much below reference.

    On the other hand, it makes sense. If I had to turn up the volume 30 decibels louder to achieve reference level, the noise would be unthinkable, and I can't imagine a movie theater at that level. Everyone who ever saw Independence Day would walk (or crawl) out deaf.

    It would also seem to explain why in so many films, no matter how loud they are, it's hard to hear the dialogue until the volume is within 5-10dB of that level.
     
  10. ScottAndrew

    ScottAndrew Stunt Coordinator

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    On second thought, though, that doesn't seem right for two reasons:[*]Most of these articles indicate that reference is at least in the vicinity of 0dB on the volume display. When I calibrated to 75dB, I was at -27 on my VR-407. That seems to indicate that -27 is not reference.[*]Second, I read everywhere that most subwoofers cannot play most material at reference level, while my VTF-2 plays just fine at that 75dB level. That also seems to indicate that it is not reference level.[/list]So is that volume at which I calibrated to 75dB actually 30dB below reference?



    Thanks for your help. I'm so confused.



    Scott
     
  11. Steve_Ma

    Steve_Ma Second Unit

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    Scott,

    Calibrating to reference is typically doing two things.

    First, you are setting up all speakers to put out the same SPLs at a given volume and...

    Second, You are resetting the actual value associated with 0 on the master volume itself. You are recalibrating your master volume so that 0 will give you SPLs of 75db. it will be your new "reference" point.

    This second piece is certainly less critical. It really doesn't matter where your "reference" point is on the volume control as long as you are aware of it. In your case it sounds like -27 is now "reference." The reason most people like to reset 0 as their reference point is so that they have a common sense of what "reference" actually means. Think of it this way: When someone says to me,

    "I bottomed my sub playing The Phantom Menace intro at -5."

    I know just what that person means. They were listening at -5 on their volume dial (or 5db lower than the "reference" standard). Since my system is calibrated the same way, I know just how loud that really is. I think you'll find that most people listen, for instance, at -10 to -20, depending on the material being played.

    I hope this helped.

    --Steve
     
  12. Vin

    Vin Supporting Actor

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  13. Leo A. Chimo

    Leo A. Chimo Agent

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    Does anyone know what level below reference the "Sound & Vision: Home Theater Tune-Up" DVD test tones are at?
     
  14. Kenny Booth

    Kenny Booth Stunt Coordinator

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    If I set my AVR master volumn to 00db and run the AVR's test tones I don't think I could adjust the spl down to 85db. On my Denon 00db is almost wide open.

    If the test tones created by the test disk are at a much lower SPL than the test tones created by my AVR then I understand. If not???
     
  15. John Garcia

    John Garcia Executive Producer

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    Kenny, read Steve Ma's last post again. Your answer is there.

    I calibrated my SR6200 at -10 volume. 0 is too loud, and even -10 is above what I normally listen to most movies/music at, but I wanted my ref level to be what I consider to be loud but tolerable.
     
  16. Vin

    Vin Supporting Actor

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  17. jeff lam

    jeff lam Screenwriter

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    I think some of you are a little confused still. I'll take my shot at explaining this now.

    First, 75dB is NOT reference level, nor is 85dB. These levels are recorded at -30 and -20 on VE and Avia because if you had to listen to test tones at 105dB without earplugs you would cry cause it was so loud(very anoying tones).

    I believe reference level is the THX standard.

    Peeks raching 105dB for the main channels and 115dB for the sub. Your receiver is not automatically set up to be at reference at volume "00". You have to play the VE tones and turn the volume up till you reach 75dB on your spl meter. This could be -10 on your receiver, it could be -20. for me personally it's -16 on my Yamaha. Some receivers can adjust the main/center/surrounds level so many try to adjust it so the reference(75dB with VE,85dB with Avia) is 00. This applies to denon receivers mostly. My yamaha can't adjust the level of the mains without the master volume so my reference can never be 00 on my receiver.

    Reference level is extremely loud to me, my usual listening level is 15 to 25 dB below reference and I have no trouble hearing dialogue.

    Remember... VE/Avia is recorded at 30 and 20dB below reference just to spare your ears while adjusting levels. When you measure 75dB and 85dB on your meter at a given volume on your receiver(lets say -17.5 for example) this is your reference level. When you want to watch a movie at full reference, turn up your receiver to -17.5. However, be carefull because not all speaker systems/subs are capable of clean playback at these levels. You coould bottom your sub and distort your mains if they are not up to the challenge of reproducing reference levels in your room.

    Hope this helps a little.
     
  18. John Doran

    John Doran Screenwriter

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    ok. now i'm confused.
    my understanding of calibration was that the avia test tone allowed you to determine what level your volume would have to be to produce an SPL of 85db, not 105db/115db.
    in other words, i have always been under the impression that calibrating your system so that the avia test tones read 85db at, for instance, -20 on the volume, meant that in order to achieve reference level volumes, you'd have to turn the volume up from -20 to 0 - a gain of 20db.
    NOW it seems that people are suggesting that whatever volume setting you're on when you calibrate the avia test tone IS reference level when listening to regular source material. so, if i get 85db with avia at -20 on my volume, playing back "episode 1" or "gladiator" at -20 will give me peaks of 105db/115db.
    is this right?
    listening to movies at the volume that gave me 85db with avia just does not seem very loud to me....
     
  19. Phil Iturralde

    Phil Iturralde Screenwriter

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    Jeff - the test signals encoded in following sources are "REFERENCE Level" and the equipment playing it back should use the following SPL values (Encoded Digital Test Signal) for proper REF Calibration.
    Video Essentials = 75 dB
    AVIA & Sound & Vision DVD = 85 dB
    Dolby Digital AV AMP/REC = 75 dB
    THX AMP = 85 dB
    You'll notice in the following GRAPH from http://www.hometheaterhifi.com/volume_7_2/feature-article-misunderstood-lfe-channel-april-2000.html
    Choose 75 dB for Video Essentials, DeLos DVD Spectacular and your internal AV Dolby Digital AMP/Receivers.
    So ScottAndrew - if you cannot dial your Volume Knob to "0", then seperately adjust your HT speakers to 75 dB, then -27 (VR-407) @ 75 dB is REF Level Mark.
    Phil
     
  20. ThomasL

    ThomasL Supporting Actor

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    I just wanted to note that you also don't have to balance your speakers using the reference level. For example, my room is small and my poor ears can't even take the test tones at 85db [​IMG] so I calibrated using Avia at 60db (-36 on my receiver's volume control) which is about where I listen to movies (usually -5db lower). Now, if I truly wanted to know what volume setting on my receiver gives me reference levels, I'd need to turn it up till my RS meter showed -85db. (it should probably be around (-36 - 25) = -11). And I believe that my speaker balance shouldn't change noticeably as I turn the volume up either (i.e. one channel begins to get louder than the other). This has been my experience anyhow in doing various tests.
    cheers,
    --tom
     

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