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Calibration questions

Discussion in 'Home Cinema Buying & Building' started by Mr Incredible, Sep 1, 2005.

  1. Mr Incredible

    Mr Incredible
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    Although I am no slouch when it comes to technical issues/concepts, I am nonetheless a n00b WRT HC. After many years deliberation (and no budget!) I've recently plunged for a new Denon 3805 and some S/H B&W speakers (except for a spanking new LCR600).

    Having let the auto calibration do "its thing" a couple of weeks ago and then subsequently researched the use of SPL meters and why people use them, I invested in a new meter from RadioShack (£24.99 ATM) and got my hands on an AVIA DVD calibration disc.

    Today I spent several hours messing around with most permutations I could find WRT to different set ups and adjustments.

    Basically I think I have disappeared up my own rectum :oops: because I managed to get different results where in theory I should have got the same.


    With exactly the same Meter position I ran three tests to find the correct adjustment for each channel levels.

    1. Using the AVIA audio calibration tones
    2. Using the AVIA reference tones (Pink noise)
    3. Using the Denon's own tone generator.

    Before starting each test I "cleared" the levels so that all channels were 0 dB.

    I used the same room EQ settings (Normal) that the auto calibration had calculated for a whole range of frequencies. As I would be using this setting for all playback it seemed reasonable to have the Room EQ set to "Normal" (I tried FLAT, FRONT and OFF and got wide ranging results up to 3 dB difference on the same channel for the same Gain and source signal).

    So at the listening position I started by adjusting the overall gain for a test such that the FL channel was outputting 80 dB. I then ran one signal source for all channels to get the correct levels and manually adjusted the channel level in the speaker channel level menu. Just a simple case of +/- dB for each channel to get the desired 80dB across all. I made a note of the settings before resetting to 0 dB for the other signals.

    I repeated for the other two signal sources. Set FL to 80 dB by changing the overall gain and then adjusted each channel in the manner above.

    I cannot understand why I get different results on the channels. Some channels are "worse" than others. For instance, on the SR channel there is a 3 dB difference between the three ostensibly "reference" signals.

    Here, look at this.....
    [​IMG]

    So, is the AVIA disc a waste of space?
    Should the Denon internal tones be used in preference to Pink Noise?
    Why would AVIA Calibration tones give different results to the Pink Noise reference tones?
    Is Pink Noise the preferred range of frequencies and levels for SPL setting?
    Is the Denon tone generator or the AVIA Calibration tones Pink Noise or some other variant?

    Are these results perhaps symptomatic of using the previously auto set Room EQ of "Normal" as the basis for the tests?
    Should the ROOM EQ be off for determining levels? If so wouldn't this negate any level settings when having Room EQ set to "Normal" for everyday listening?

    The tone generators all appear to have a fullish frequency composition which the SPL meter will average out in accordance to the C weighting setting. When I check the EQ levels i get a long list of specific frequencies (which appear to change for FL, C, FR etc, why?) and the dB adjustments for each speaker for a range of frequencies ranging from 57Hz to 14kHz. Is it the case that the AMP determines what the frequency ranges are that needed to be adjusted? Or is the list of frequencies in each channel a set of "fixed" or pre-defined frequencies which have shown to be representative of the spectrum of sound for the listener?

    As there is a facility to have a manual EQ for all the frequency ranges on each channel, o many people use adjustable tone generators and measure the SPL for each of these frequencies and adjust accordingly? Or is this too much bother for the home enthusiast? Or is there another way with mics and PC software and spectrum analysers?

    SO what I thought was going to be relatively straightforward task has left me with more questions than answers.

    Perhaps I should just take the SPL back and save me the headache of trying to fathom out what the fudge is going on with SPL adjustments and the so called "reference" tones used to calibrate.

    Have you fallen asleep yet? :boring: :D

    Sorry about the length and content, but this n00b likes to understand the underlying reasons for observed results!

    :thumbsup:
     
  2. Ian J

    Ian J
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    I can't answer the majority of your questions as I haven't used any of these new fangled room EQ thingies.

    Avia test tones are mastered onto the disc at 10db higher level than the internal tones in the amplifier so you need to compensate when comparing the two sets of figures.
     
  3. Mr Incredible

    Mr Incredible
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    Ian, thx for the info. Although I notivced the AVIA tones were "louder" than the amp's internal tones, isn't the fact that I adjusted the system gain so that all the tones produced 80dB as a reference start point, before starting the measurement, mean that I should get the same results (which I didn't)? I can't believe the amp introduced variances per channel just because I upped the overall gain on it for a couple of different sources.

    Also I don't understand why the AVAI gave different results for different tones on the same DVD. Odd /me thinks.

    /me confused.
     
  4. Mr Incredible

    Mr Incredible
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    As a sort of post script on this and nowhaving invested in an SVS sub :), I posted in the subs forum about calibration/set up of my system with the sub.

    Perhaps you'd like to read the thread and pass comments there? :thumbsup:
     

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