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Beware - Internal Test Tones

Discussion in 'Home Cinema Speakers' started by Brad_Porter, Nov 20, 2002.

  1. Brad_Porter

    Brad_Porter
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    Read this if you have time - its basically about my findings by using an amps internal test tones and a setup disc (like DVD Essen or AVIA) that calibrate from the source.

    I was kindly offered a lend of ‘DVD Essentials’ set-up disc (Thanks to Matt Horne) so that I could calibrate all my speaker levels to exactly the same. At current, I am not setting everything to reference (75db) level as if I do I have to lower my front three speaker levels by a whopping -7/8db as I use an Arcam Power amp for front three and the Denon looks after the rest. Obviously the Arcam or the Denons Pre-amp stage makes the signal a lot more powerful then the Denon internal amplifiers!

    Using DVD Essentials (or no doubt AVIA) and an SPL meter has really made a positive impact on my surround sound system. It has just proven to me that the internal test tones do not really work as effectively at aligning your system levels in comparison to using test tones through the source; namely your DVD player.

    For quite some time, I have felt that the my rears speakers were over powering and one sided when playing surround sound DVD's. Also, the centre channel produced quieter vocals. However, the internal Denon test tones all measured 75db so I thought the problem was down to appalling room acoustics. I was just about to spend £250 on a thick wool 300 x 200 rug and place objects on the back wall.

    Lucky for me I used the DVD Essentials disc beforehand and may I say, categorically, that 80% of these problems have now disappeared. The rears are no longer over powering and one-sided and the steering from the front to back is pretty much fantasticly improved. The low audibility speech issues have also ironed themselves out to a high degree and watching films such as ‘We Were Soldiers’ at lower levels produces a far easier to understand dialogue then before.

    The lesson to be learnt here is that setting test tones from the amplifier simply isn’t good enough to obtain a true effect of enveloping surround sound from your speakers. Also, wrongly powered speakers can over power certain parts of the sound causing a loss of effect (or dialogue quality) in others.

    The rule is simple really because, if you think about it, you really should align the speaker levels from the source you are playing from rather then the amplifier which is the mid way part in the process of source - amp - speakers.

    Trust me. The difference has been really noticeable and I would recommend anyone using there amps internal test tones to recalibrate them with either of the DVD discs mentioned earlier or some kind of well made test tone DVD.
     
  2. MalcT

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    Where can I buy/ get hold of one of these set-up discs.

    Cheers
     
  3. Bapapapa

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    Just out of interest, why, if you thought the rears were too overpowering and the dialogue (centre?) was muted, didn't you just lower & raise their volume respectively..? Surely tailoring the sound to your own personal preference is better than blindly (deafly) sticking to the 'proper' settings..
     
  4. Brad_Porter

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    When I say overpowering, I really meant that they were really 'directional' and I felt a little lob sided. By the time I had altered things up an down, I would manage to destroy the soundstage even more and would end up having to reset everything to 75db via the amp test tones! Doah!

    I dont feel that your ear can realistically set all the levels to that of almost dead accuracy. Well, not the accuracy I want!

    The biggest argument I have for using an SPL and a DVD set-up disc is that since using it (and by this I mean calibrating from the source), it’s given me the best sound I have ever heard my system produce to date.
     
  5. Mark Ward

    Mark Ward
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    Despite owning Avia I've always set my speaker levels with the processor's internal test tones.

    I've been pretty happy with the results and I've never been 100% sure what volume level on my processor/pre-amp I should set to whilst calibrating with Avia.

    Mark.
     
  6. Brad_Porter

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    To be fair, reference level is only, well a reference level!

    As long as all your speakers read exactly the same db's as each other in your 'sweet spot' and (IMO) this has been calibrated from the source (DVD player), it should sound super fine.

    It really has worked for me with the DVD Essential Disc and hope that if anyone else try's it, it improves there sound as well.

    If not, I’m a dead man.:D
     
  7. The Nightfly

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    Is your DVD player connected to your processor via a digital connection ? If so, your DVD is simply passing the 'digits' over without making any interpretation of what they mean. If you are with me so far then you'll agree that no matter what DVD player you had connected, the levels would be the same. So variations in the DVD player used are essentially irrelevent.

    When the 'digits' arrive at the processor, its the D/A converters in your processor that determine the output levels for each channel. Assuming all your D/A converters are correctly calibrated, and each is being fed with the same digital signal, each should output the same signal level.

    Assuming your D/A convertors ARE correctly calibrated, I don't see why this should give a different result to injecting an internally generated test-tone identically into each channel.

    Allan
     
  8. petrolhead

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    Hmmm, technical Allan :)

    But if he feells there is an imprivement then I for one would try it.

    So on Friday I will setup the 3802 using its own test tones and then check them using my DVD Essential disk.

    Could be interesting?

    BTW Aidan is popping round with some Kef Q8s for me to try.

    Boys and toys :D
     
  9. The Nightfly

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    I don't think its anything to do with the fact that one set of test tones comes from a DVD player and one set is generated internally. I think its probably caused by the test tones themselves being different in frequency content.

    They are both meant to be 'pink' noise - ie white noise that's been adjusted to produce a spectrum that has a real-world bias. What this actually means in practice is probably open to a bit of interpretation.

    I wouldn't be surprised if the two sets of tones sounded quite different and therefore results varied dependent on the fact that speaker output and room interactions vary by frequency. I bet if you set levels identically for all channels by measuring the voltage on the amps speaker terminals then you wouldn't see this variation. Its only when you introduce different types of speakers with different amplitude response by frequncy characteristics and room responses that vary by frequncy and which part of the room the speaker is located in that you get these frequency dependent results.

    So there :p

    Allan
     
  10. Brad_Porter

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    OK, so I gather that you have tried this (from source and amp test tones) before you commented? You used the word 'I think' a lot rather then 'my evidience'. :D

    I am not desoputing the test tones. What I am saying is that when I calibrate from the source, the sorround effect of DVD's is far better then when calibrated from the test tones on the amp. I can audibly hear the difference.

    Also, surely you can agree that calibrating from source is better then calibrating from the midway point such as the amp?

    So there to you too. :p

    I tell ya, tbis forum is becoming really childish. :D
     
  11. petrolhead

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    Hmmm :D :D

    Anyway getting back to the point. I would be interested in the results of the following test:

    Setup you system using the DVD then check it against the Amps test tones. Ignor what the level is, just see if all the levels are still the same. Let me know.

    :) Sound like I have given you some homework. Hope you do not mind, this is because I am away at the mo and can't do the test myself.

    Peter
     
  12. Brad_Porter

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    Sounds interesting actually. In a nerdy kinda way! :D

    I will give this ago at the weekend and post the results - I should have really done this myself before!
     
  13. The Nightfly

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    Hey it was a joke, lighten up, and not really directed at you but at petrolhead (who I know personally) and his 'hmmm, technical' comment, and that even though I doubt the actual DVD player in use has any bearing (its the spectrum of the tones themselves that make the difference) I do have an explanation for what is happenning.

    Allan
     
  14. Jase

    Jase
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    Mine are the same.;) Checked this again last night. 0db on the volume level, internal test tones balanced to 75db gives the same results as using the AVIA disc and test tones balanced to 85db and vice versa.:D

    It does vary depending on the amp though, my Denon (KA1SE) is spot on, the old chaps Denon 3801 gives different results with AVIA against the amps internal test tones. The levels have to be upped all round by about 5 or 6 db when AVIA is used.
     
  15. kevenh

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    To me, using a setup disk to set levels gives a more real life test than just using the amps internal tones.

    We're using more of the chain, start to finish. Not just the later stages.

    I will have to set a side some time to compare internal to external tones.

    (oh! Just noticed that there have been a few posts between my 1st read this morning, and writing this. Looks like you've already covered what I say)
     
  16. petrolhead

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    Sorry to resurect this one BUT....

    Today I finally did the test I have been meaning to do for a couple of weeks now.

    I setup the speaker levels using the 3802 test tones and got them all set to 75DB.

    I then tried the test tones on the Ultimate DVD Paltinum.

    Well they are now all over the place with those tones! +- 1-3 DB

    Why could this be?

    So going back to Brads question, which will be correct, the Denon or the DVD.

    Any thoughts.

    Any time you want to comment Allan, please feel free :)
     
  17. The Nightfly

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    These test tones on the Ultimate Platinum DVD - is the purpose meant to be for confirming channel identification only or are they puposefully recorded at equal levels and meant to be used for setting identical channel levels ?

    Allan
     
  18. Cool-hand

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    Has anyone tried using the Fox DVD Demo Disc THX optimiser or the test section on Cast etc...

    Logic seems to say that the Denon processor should be the most accuarte as most discs vary in amplitude and maybe certain 'Test discs' are not highly callibrated (ie each fuzzy buzzy white noisyzz channel not at the exact recorded noise level)
     
  19. petrolhead

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    No No

    These are proper test tones for setting up the speaker levels. It has a complete Audio section.

    You will have to have a look for yourself. It covers LFE, rattle tests, various frequency levels. It also has a section for setting up the PJ.

    So back to my question folks..........?????
     
  20. The Nightfly

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    So the test tones on the DVD are recorded at equal levels and the test tones in the amp are at equal levels but you are measuring discrepencies of up to 3db. To put this into context, 3db represents a doubling of power (or in voltage terms, a 41% difference).

    To get this kind of difference (or error), the likely options are:

    - the DVD's test tones are not recorded identically across all channels
    - the Amps test tones are not identical across all channels
    - both sets of test tones are correct in themselves but are different types of tone and so you are not comparing apples with apples.

    An example. Lets say the amp's test tones have a much weightier sound to them than the DVD test tones - ie they contain more bass content. Lets say you apply this test tone across the front three speakers where the main Left and Right speakers have a more extended bass response than the centre speaker. When the signal is switched to the centre speaker it will measure lower than the other two because it's got less output lower down, giving an overall lower SPL reading, so you'll turn this speaker up to compensate.

    Now if the DVD's test tones were lighter sounding (ie they contain less bass content and more mid range) then the centre speaker's weakness in the bass would have less of an effect on the result, giving a similar overall SPL reading and you wouldn't have to turn this speaker up to compensate - in fact, if you'd previously calibrated with the amps tones in this example you would now be turning the centre speaker down.

    Which one is correct - I would say the one with tests tones that are closest in match to the frequency response of the smallest speaker in your setup. ie a broad enough spectrum to ensure that the tones are representative of real soundtrack material but not so broad that the limited response of one or more speakers is influencing the results.

    Just had another thought, what if bass-management in the amp is kicking in when test tones are played from the DVD but the speakers are run full-range with the internal test tones. Try it again with all speakers set to large to see if the results are similar for both sets of tones.

    Allan
     
  21. petrolhead

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    Hi Allan

    Yet again you have excelled in your reply :)

    I think I get what you are saying. So therefore each set of test tones will probable gice a different result. Maybe thats why a few THX DVDs have a set of tones so that you set up your system to suit the sound of that film (The way the director intented)

    The speakers are set to large.

    What I am going to try is the THX optomiser on the AOTC DVD.

    If I get different settings again then realy the only set variable is the amp and therefore will stick with its tones.

    Peter
     
  22. bob007

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    The test tones on these discs aren't for callibrating speakers, it even says that on the introduction before you play the tones, they are basically there just so you can check the speakers are in their correct position.

    Allan,

    Don't know if the bass management kicks in or not when the test tones are played, but know that adjusting the "bass" and "treble" controls makes no difference to the test tones.
     
  23. petrolhead

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    So why the difference Bob
     
  24. petrolhead

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  25. The Nightfly

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    :D .

    BTW, petrolhead, my visit to your house has cost me dearly !

    Allan
     
  26. petrolhead

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    Don't tell me. Prog scan DVD?

    You should have kept your eyes shut :D
     
  27. Jase

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    Might give it a go with the sound meter set to A-Weighting. Roger Dressler works for Dolby Labs so he must know what he´s talking about. :)
     
  28. petrolhead

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    Is that right.

    Yeh then he should know.
     
  29. bob007

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    Found something that may explain a little more on the differences of the different weighting values. Will need someone with a bit more knowledge to explain the different values in simple english, for me anyway. :D

    What does dB(A) or "A-weighted" mean ?

    Noise was not of particular concern at the beginning of the century. The first electrical sound meter was reported by George W Pierce in Proceedings of the American Academy of Arts and Sciences, v 43 (1907-8).
    A couple of decades later the switch from horse-drawn vehicles to automobiles in cities led to large changes in the background noise climate. The advent of "talkies" - film sound - was a big stimulus to sound meter patents of the time, but there was still no standard method of sound measurement.
    The first tentative standard for sound level meters (Z24.3) was published by the American Standards Association in 1936, sponsored by the Acoustical Society of America. The tentative standard shows two frequency weighting curves "A" and "B" which were modelled on the ear's response to low and high levels of sound respectively.
    The most common weighting today is "A-weighting" dB(A), which is very similar to that originally defined as Curve "A" in the 1936 standard.
    "C-weighting" dB(C), which is used occasionally, has a relatively flat response. "U-weighting" is a recent weighting which is used for measuring audible sound in the presence of ultrasound, and can be combined with A-weighting to give AU-weighting. The A-weighting formula is given below.
    In addition to frequency weighting, sound pressure can be weighted in time with fast, slow or impulse response. Measurements of sound pressure level with A-weighting and fast response are also known as the "sound level".
    Some sound level meters can measure the average sound level of a noise over a given time. It is called the equivalent continuous sound level(L sub eq) and is A-weighted but not time weighted.


    [​IMG]
     
  30. EvilMudge

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    Sorry Bob, what exactly was it you wanted explaining?

    dB(A) is basically a map of human hearing - if you play a tone at the same level in reality what you will hear will sound louder or quieter depending on the frequency. It's not the actual SPL being produced, but it is how most people will hear it - therefore to get 75dB result on a SPL meter weighted with A, bass & extreme treble tones either have to be played very loud, or made up for by mid range ones.
    When playing pink noise (audio band all frequencies equalised) the SPL is most dependant on the midrange, with an A weighted meter.
     

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