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THX Optimode Test Tone Vs Amps Test Tone

Discussion in 'AV Receivers & Amplifiers' started by Demon, Jan 12, 2003.

  1. Demon

    Demon
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    Hi...

    When I originally setup my new amp/speakers, I sat in the preferred listening seat, and then adjusted the levels to each channel to give me the same volume when using the amps Test tone.. as you do....

    But, I then used the THX Optimode setup that came on one of my Film DVD's and its test tone setup part gives me something completely different...


    Channel, Amps Level, THX Optimode Level
    FL/FR, 0, 0
    CENTRE, 0, +2
    SL/SR, -2, +3

    SO why is there such a discrepency?

    My Kit
    AMP: DENON AVR3802
    FRONT SPKS: B+W DM603 s3
    CNTR SPKR: B+W LCR60 s3
    REAR SPKS: B+W DM600 s3
    DVD: Toshiba 220E

    I really think that leaving it set at the THX levels would ruin many films... (Especiially a Dolby Digital Demo disk) but thought that the THX film in qiestion (Toy Story 2) did sound better when set to its THX reference levels...

    ANy ideas, or do I need 2 sets of settings?
     
  2. HotblackDesiato

    HotblackDesiato
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    From recollection there's a note on the THX audio optimizer included with some DVDs to the effect the tones are not for level setting.

    spence
     
  3. Demon

    Demon
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    They onscreen instructions tell you to adjust your system so that the same volume level is output from each channel. and adjust as necessary.. with no notes in/on the DVD....
     
  4. bob007

    bob007
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    All the THX set up extras I have seen say that it is to be used as a check for speaker postions, it can be seen on the screen before you start the white noise test.
     
  5. Demon

    Demon
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    Indeed it is to check speaker placement etc, but the pertinant point is

    "From the optimum listening position, the audio level should appear equal from each speaker except for the sub which is limited to 120Hz"

    So if the volume levels arent equal when sat in the optimum listening position.... this implies that you need to equalise the levels by which ever method is appropriate, and in most cases this would be the AMP..,,

    or am I interpreting this incorrectly?
     
  6. bob007

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    You use the amp by which ever method your setting your levels by, the difference being that when you calibrate the speaker levels via the dedicated test disc like THX Optimode, you are bypassing the amps internal test tones and have to set the volume manually to 0db.

    Think most will agree that setting the speaker levels via source (dvd player) with a dedicated test disc and spl meter is the most accurate way as the amps internal test tones which can be less accurate.
     
  7. Demon

    Demon
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    Thanks Bob, that makes sense...

    Normally I follow this procedure
    1. Use the AMPS test tone to setup equal volumes are normal listening volume.
    2. Use Dolby Digital Demo disk to tweak these to give me a balanced soundfield with good effect location, this is not too far away from the results of step 1... and am sure would be close as well to SPL meter settings.

    but I am a bit worried about this particular situation, since the rear is so dominant..

    I suspect I will have to do some more tests, with other THX Optimode films, and other DTS/DD films, and see if the THX Optimode requires me to change the channel levels for jut those...

    I agree with Bob, that since the DVD is the source of the audio, then it makes sense, that this creates the test tones, and the rest of the system is set according to this, as I am not sure where the AMP test tone is injected in the proceedings, although on one Yamaha DSP i did some test kit for, it was the actual DD Decoder DSP that generated the test tones...

    If I find anything major out, I will post the results...
     
  8. HotblackDesiato

    HotblackDesiato
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    Sorry i've obviously mistaken what THX optimizer you're referring to.
    Thought you were on about the THX routines included with movies. On my TPM disc there's a note something like "This test is not intended to be used to set exact speaker levels. Refer to your processors manual for the proper set-up procedure".

    Once again, apologies for muddying the water,

    spence
     
  9. Stuart M. Robinson

    Stuart M. Robinson
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    Guys,

    Optimode test tones are, aside from those upon one disc, all inaccurate. See:

    http://www.smr-home-theatre.org/optimode/

    After I pointed this out to THX (who were at the time unwilling to admit their error), the on-disc calibration scheme was corrected and re-launched as Optimizer.

    Optimizer can be used as a guide, but leave Optimode well alone.


    Stuart M. Robinson
    SMR Group - http://www.smr-group.co.uk/
     
  10. Demon

    Demon
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    Cheers for the replies....

    I did some research, and although their is a lot of info regarding their incorrect reference levels, they should theoretically be all the same level....

    I realised that I originally used an Optimode Disk that claims to allow you to set the levels, I then found a disk with the THX Optimizer, and they've removed statement about checking levels are equal.... to save any confusion over 30dBbfs and 20dBbfs... and I think its fair to say that if you just tried to equalise the volumes by ear, you will ernd up with a greatly exaggerated rear channel...

    So I went back to the AMPS internal test tone... and am Happy now that this is closer to what is required. I may get an SPL and set it up properly to reference levels, I hope that at 0dB on the amp, that the levels needs greatly reducing, cos if my cinema was that loud... I'd be deaf....
     
  11. shodan

    shodan
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    QUESTION

    Hiya, not worthy of it's own thread so I thought I'd ask it here as it's similar...

    oN MY AMP - yAMMY rxv730RDS - and indeed on the one before I noticed that the test tone doesn't sound the same through each of the front main speakers. I don't mean louder or quieter but rather a higher / lower tone. Is it my hearing (of course not!!) or am I going round the bend (quite likely) or is this normal? And more importnantly, how can I test it to find out which it is????


    Thanks



    PS Of course, this does make setting the speakers via test tone a tad difficult!
     
  12. Demon

    Demon
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    The Test Tone generated is White Noise, or Pink Noise(can;t remmeber), anyway it is the same signal for all channels

    Of course, if one of the drivers on the speakers is duff, then it will alter the sound, and you would notice it.
    The normal scenario, is that due to furniture/walls/doors the sound from one is reflected more/less then the other, and this can make them sound differently...

    To check, you can always stand them in as open a position as possible sat next to each other... then sit closish to them, this resuces the effects of reflections/nodes/etc and should at lest tell you if a driver is duff...

    I suppose theirs loads of ways of checking this.,..


    Over to the experts....
     
  13. shodan

    shodan
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    Both speakers seem to be in perfect working order and when I listen to, say for instance, a voice in stereo, it sounds the same from both speakers. Maybe it is the reflection / diffusion of the soundwave changing the tone of the signal I hear.....?

    Thanks.
    John
     
  14. HotblackDesiato

    HotblackDesiato
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    If you want to be sure you could swap the speakers...that is move speaker A to speaker Bs location and visa-versa. If it's down to room acoustics the high and low tones should stay in the same location, and not move with the speakers.

    Clear as mud,

    spence
     
  15. shodan

    shodan
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    DOH!! Of course!!! I shouldn've thought of that!!! Thanks for the reminder!!!

    Will let you know how I get on......
     

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