Calibration Questions

Discussion in 'Archived Threads 2001-2004' started by Arron H, Jun 4, 2002.

  1. Arron H

    Arron H Second Unit

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    Okay, I know that this topic has been beat to death but after going through many of the threads on calibration, I still have a few questions:

    Assumption: You have already calibrated your system using VE, Avia, or S&V.

    Question 1: When you play back a DVD at the reference level on your receiver that you used to calibrate, is it theoretically playing back at 105Db? For example, the reference level for calibration on my Yamaha RXV-1200 ended up being -18.5Db when my mains reached 85Db. When I play back a DVD with the receiver volume at -18.5 is it theoretically supposed to be hitting 105DB?

    Question 2: The Radio Shack SPL is supposed to read about 4Db high so if I measured my sub at 85Db using C weighting and the slow setting, it is actually playing at about 89Db or 4Db hot?

    Once again, I know these questions have probably been asked more than once but I just want to make sure that I've got it straight. Thanks for everybody's input.
     
  2. Arron H

    Arron H Second Unit

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    Oops, regarding question 2, I meant that the RS SPL meter reads about 4Db low rather than high, so a reading of 85Db is really 89Db, correct?
     
  3. Vince Maskeeper

    Vince Maskeeper Producer

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  4. Arron H

    Arron H Second Unit

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    Hi Vince,

    Thanks for the reply.

     
  5. Vince Maskeeper

    Vince Maskeeper Producer

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    Yes.

    As I've said many, many times-- ignore what the digits your volume is set at- instead worry about output.

    The position your volume knob is on in order to achieve proper output with a calibration disc tones, that is ref level. In your case, this (I assume) is -18.5, but it could be a different position on a different system or in a different room (the important part is you determined this volume position measuring output with calibrated tones and a SPL meter).

    So when you place your receiver at -18.5 volume position, and you playback a DVD- the peak sound from any one speaker should be 105db (115db LFE).
     
  6. Arron H

    Arron H Second Unit

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  7. Jonathan Smith

    Jonathan Smith Stunt Coordinator

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    I have a very similar question. When doing the calibration on my receiver, the manual says:

     
  8. Vince Maskeeper

    Vince Maskeeper Producer

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    Most receivers will set the volume knob to 00 when you turn on internal test tones. Usually 00 is the expected ref level (in your post you said you don't hear anything at 0, when most modern receivers start at -60 and go up to 0 [and some allow boosting to +4 or +6]).

    So the basic answer is this:
    1) If you plan to calibrate using the internal test tones, turn them on (the receiver will automatically set the main volume to 00). Adjust the speaker levels so that the SPL meter measures 75db of output. Go through all the speakers until they all measure 75db on the meter. Now, your system is calibrated, and the 0 position on the knob will be "ref level".

    2) If you'd like to use AVIA, you can do the same as above. Set your volume manually to 0, then use the Avia tones to adjust the speaker levels until you get 85db on the meter.

    Technically speaking, if you're using AVIA you don't have to set your master volume knob to 0 to set ref level (as long as you get the proper measured output)- however most people do (and most products suggest this) as 0 is very easy to remember...

    Hope that answers your question.
     
  9. Harold_C

    Harold_C Stunt Coordinator

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    The 4 dB "error" on the Radio Shack meter is not just a myth. In their instructions to recording engineers setting levels in a Dolby Digital mixing studio with an SPL meter, Dolby recommends setting the subwoofer level so that it reads 4 dB low on the meter -- i.e. if you are aiming for a 75dB calibration, you would actually set the sub to read 70 to 72 dB on the meter.

    The actual difference will vary from system to system. The C-weighting of the meter means that the actual output of the subwoofer is higher than the meter reading at very low frequencies. Combine this with the fact that you generally have some significant peaks and valleys in subwoofer response and that's why the "inaccuracy" shows up.

    I have my sub set to 72 dB for a 75dB calibration and it seems to blend perfectly with the mains -- although it's lower than I would have orginally set the sub. I think Dolby's advice is quite good for a starting point.

    Having said that, I believe that 99% of folk have their subs set too high. Basically, when listening to regular music (say an acoustic guitar and singer), there shouldn't be ANY tonal difference with or without the subwoofer -- assuming half-way decent bookshelf or larger main speakers. Only on very low bass notes should the impact with the subwoofer be noticeable, and even then, it's more physical than audible.

    Psycho-acoustically, we tend to set our subwoofers at a level so that we KNOW there is a subwoofer in the system at all times "wow -- listen to that bass!" That's understandable, but it's also too high a level for proper integration with the main speakers and it tends to make Dolby Digital bass effects seem "disembodied" from the rest of the frequency spectrum. The subwoofer bass messes up the harmonic content and makes midbass sound muddy and thick. I think that's why folk also think that lower crossover points "sound better" -- they are compensating for the harmonic mush of having the sub levels set too high.
     

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