Sub Experts: A Few Sub Calibration Questions

Discussion in 'Archived Threads 2001-2004' started by Richard Burzynski, Dec 21, 2001.

  1. Richard Burzynski

    Richard Burzynski Second Unit

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    (1) Is using the internal receiver/prepro test tones good enough? Also, do the receiver manufacturers use a particluar db reference point? I think I read that B&K uses 75db.

    (2) Video Essentials uses 75db as a guide. Avia uses 85db. I own a copy of the Dolby Spectacular (V1) DVD. I believe it has speaker calibration tones as well. Does anyone know its reference point (75db, 85db)?

    (3) I plan on using two passive subs and an amp that does not have a volume control. Is the receiver/prepro sub level settings good enough? Or should I hook up a stereo preamp (in between the receiver's sub out and the sub amp) inorder to achieve volume control over the sub amp? I do have one in the closet, but is it necessary? And why?

    (4) If you think that I should use the preamp as a volume control, what volume setting should be my starting point?

    Thanks.

    Rich B.
     
  2. Bob Christensen

    Bob Christensen Stunt Coordinator

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    Reference point is just that: reference. As long as it approximates your "typical" listening level, and is not changed throughout the course of your setup procedure, it shouldn't matter which reference point you choose. If you have a wide latitude in volume adjustments through your receiver, that may be enough. Try it before adding more electronics to your line. My bet is that you will need some sort of volume control to balance your system, though.
     
  3. Bob Christensen

    Bob Christensen Stunt Coordinator

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    Oh, BTW, I'm no expert :b Just an enthusiast.
     
  4. Richard Burzynski

    Richard Burzynski Second Unit

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    Bob:

    Thanks for the reply.

    I realize that any reference point will allow me to balance all speakers & sub. But I'm interested in doing it via a calibrated signal (disc), so that I can know (once and for all) what exactly 105db Dolby Reference sounds like in my HT.

    I, of course, will probably not spend much time listening continuosly at that level (ouch!), I just want to calibrate my system using that as a guide.

    Rich B.
     
  5. Scott Page

    Scott Page Stunt Coordinator

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    Richard,

    Bob makes some good points. I've found that what is "reference" varies quite a bit with the source. Reciever test tones are "supposed to" be set to give you reference levels and so are the VE and AVIA test disks. Then there is the Optimode DVD's. My Denon reference levels are about 7 dB's less than the reference level with AVIA and about 2 dB's louder than Optimode. So which is correct? The AVIA is much louder than the Optimode tests. Since I couldn't stand to listen at AVIA levels, I choose the set mine using the Denon with a 1 dB bump up in the surrounds as suggested by Optimode testing that shows my surrounds to be a little bit weak.

    I have asked the same questions, and so far no one can tell me diffinatively that my Denon is incorrect and not the AVIA tones.
     
  6. Wayne A. Pflughaupt

    Moderator

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    Hi Richard,



    I’ll take a shot at some of your questions.
    1. It depends on how good they are. For instance, my Yamaha DSP-A3090 has 1/6-octave test tones, but the lowest frequency is only 35Hz. In my opinion, you need at least 1/6-octave tones from 20Hz to 100-125Hz. Finer resolution never hurts, but good results can be achieved with 1/6-octave tones.
    2. Sorry, I don’t have either one of these.
    3. The receiver’s sub level control should be sufficient. As long as it is adjustable it will serve as your “volume control.” As Bob noted, no reason to put more gear in line than you need. However, if you do find you are not getting enough signal into the sub amp, you might consider an outboard electronic crossover instead of a regular pre-amp. It will give you an adjustable signal boost, and steeper slopes than the 12dB/octave fare usually found in receivers.


    Happy Holidays,

    Wayne A. Pflughaupt
     
  7. Vin

    Vin Supporting Actor

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  8. Jimmy P

    Jimmy P Stunt Coordinator

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    The difference between a calibration disc vs. receiver test

    tones is that a cal disc uses your complete audio chain ie:

    dvd player,connection between dvd and receiver,receiver etc

    As far as test tone reference levels,75dB or 85dB,85dB is

    the level movie theaters are calibrated to,but most home

    users find 85dB is to loud and find 75dB acceptable.If your

    system/setup is fairly linear,there will not be much of a

    difference in calibration between 75 or 85,just a dB or two

    here and there.

    You should be able to use the receivers sub-out level to

    control your remote amp to the subs,provided it has enough range of operation.
     
  9. Scott Page

    Scott Page Stunt Coordinator

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    Quote: "The difference between a calibration disc vs. receiver test tones is that a cal disc uses your complete audio chain ie: dvd player,connection between dvd and receiver,receiver etc"

    True, but for me testing both ways shows that the various channels are about the same and the only difference is the overall loudness. Your mileage may vary.

    Quote: "As far as test tone reference levels,75dB or 85dB,85dB is the level movie theaters are calibrated to..."

    I might be wrong, but I believe this to be stated slightly incorrect. The movie theater reference level (actually the THX level) is 105dB for all channels and 115dB for the sub. Now, just what type of test tones and recorded levels each theater uses to achieve this is unknown to me. AVIA is recorded at reference minus 20dB or 85dB, and VE is recorded at reference minus 30dB or 75dB. Most reciever test tones are in theory also at reference minus 30 or 75dB. Used properly both AVIA and VE should produce roughly the same results. I have not yet used VE so I don't know how close it comes to AVIA.
     
  10. Jimmy P

    Jimmy P Stunt Coordinator

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    Scott,

    The levels you are refering to(THX 105dB and 115db for lfe)

    are the maximum levels during playback for a system initially calibrated.example:THX 75dB=105Db max,85dB=115dB lfe max.
     
  11. Scott Page

    Scott Page Stunt Coordinator

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    Yes Jim I'm aware of that. The point is that the reference level IS the peak level and NOT the test tone level used to calibrate it. The test tone level can be anything. I could make a test tone disk with levels at reference minus 50 in which case I would calibrate using it at 55 and should in theory acheive the same peak levels as using AVIA at 85. The test tone level is NOT the reference level, but is a tone recorded at a reduced level to save your hearing and nerves while you calibrate.
     
  12. Bryan Acevedo

    Bryan Acevedo Second Unit

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    Also, depending on your receiver, I wouldn't boost the sub level (i.e. go into the + range) as many receiver sub outputs start going into serious distortion when boosted. So you may have to add a separate pre-amp to the sub amp, so that you don't introduce distortion.

    Also, with my Denon 3802 internal test tones, I calibrate at a volume setting of 0 to 75 db. This is because the internal test tones are 30 db below the maximum reference level. If I use Avia, the test tones come out as 85 db for every single channel, without adjusting anything. So in my case, the internal test tones are extremely accurate, even from channel to channel. I think older receivers may not have accurate test tones, but most new stuff SHOULD be relatively accurate. Again, that is a generalization, but in my case, it is dead on. If it isn't on, usually it is because the room is interacting more with the louder signals from an 85 db signal, and not because the signals themselves are inaccurate.

    Bryan
     
  13. Scott Page

    Scott Page Stunt Coordinator

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    Bryan,

    Your info is interesting. I have the Denon 3801 and it isn't even close to the AVIA level. Interesting. I've got to get VE and compare it.
     
  14. BruceD

    BruceD Screenwriter

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    If you have an RS SPL meter, you can tell which method of setup comes closer to the absolute reference level (receiver or AVIA/VE DVD).

    Audition the DD or DTS introductions on many DVDs with the volume set to reference level 0 (zero) or all the way up and use the SPL meter to measure the level at your seat.

    What SPL readings did you get for each setup method?

    BruceD
     
  15. Jimmy P

    Jimmy P Stunt Coordinator

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    It matters which way your looking at setting up the calibration,and yes you are trying to achieve maximum levels

    To reach those levels the initial calibration level is 85dB

    True you can use any reference level you like,but if you use the -50 level in your example and calibrate at 55,you will not get theater level maximums.

    To replicate theater playback,you start with a pink noise reference recorded at 85dB,and adjust all channels to read

    85dB with a sound meter or better yet an rta,then if you have a home system with enough power you will be able to get those maximum theater levels upon playback.
     
  16. Scott Page

    Scott Page Stunt Coordinator

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    I have a meter and can do that, but I'm not sure how that would help as I have no idea what level the DD or DTS trailers are supposed to achieve. Also the level changes constantly during the intro run.
     
  17. Scott Page

    Scott Page Stunt Coordinator

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    Jimmy,

    I think you may be missing the point. If I record a test tone at a reduced level of say ref-50. Then calibrate using that test tone at 55. Then I get peaks of 50+55 or 105db. Which IS the reference level. If I record a test tone at ref-10, then I calibarate at 95, which gives me a peak level of 10+95 or 105. So the ref-50 tone and the ref-10 tone will give me the exact (or close enough) peak level as AVIA (recorded at ref-20, calibrate at 85), or VE (recorded at ref-30, calibrate at 75), or whatever. The level the test tone is recorded at is irrelevant provided you calibrate at the appropriate level to reach a peak of 105.

    The reference level is NOT 85dB. That is just the level you would use for AVIA (and any other test tones recorded at ref-20). I have seen literature state that the reference level is 75dB. That is incorrect and misleading as it depends upon the source test signal recording levels. The THX reference level is always the PEAK level and not the calibration level as that level will change as it does if you are using AVIA or VE and most recievers.
     
  18. Phil Iturralde

    Phil Iturralde Screenwriter

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    I will just address Question 1 & 2:
    QUESTION
    Thank you Roger!
    Phil
     
  19. Richard Burzynski

    Richard Burzynski Second Unit

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    Excellent stuff guys, keep it coming!

    Phil:

    "Dolby makes sure the internal noise is calibrated in level and meets certain spectral requirements. (as per Mr. Dressler)"

    That's great.

    Safe to infer that internal receiver test tones are at 75db (just like VE DVD)?

    Thanks.

    Rich B.
     
  20. Bryan Acevedo

    Bryan Acevedo Second Unit

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    Thanks Phil - those are the posts where I originally got my info from, but couldn't remember where they were. I only use Avia for the sweeps and video setup, not for level setting. And in my case, it is identical, and according to Dolby, my internal test tones should be more accurate anyway. Since we are usually calibrating for Dolby Digital Reference - I will stick with the method that Dolby themselves recommend.

    Bryan
     

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