Repost: Test Tones For Evaluating Your LFE Pad

Discussion in 'AV Receivers' started by Vince Maskeeper, Dec 21, 2004.

  1. Vince Maskeeper

    Vince Maskeeper Producer

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    Since I got two emails in the last month asking about these tones, I thought it might be time to post it again, for anyone who wanted them... this is a repost from a couple years back:

    In reaction to the fact that the 6 channel pan on the original Avia appears to be flawed, I have authored 2 DD test tones which will allow people to test the level of LFE vs the level of rerouted bass from other channels.

    The idea is that the 40hz sine wav in any channel, with the speakers set to small, will be rerouted to the sub. Since it is the same freq, coming from the same sub, with the meter in the same position- the only variable in the level of output would be the amount of signal being sent by the preamp. If the decoding is done correctly, the main channel tones and the sub tone should be within 1 db of one another.

    1) dd140hz1.wav: A 40hz tone at -20 which repeats in each of the 6 channels, 5 seconds at a time (Left, Center, Right, Left Surround, Right Surround and LFE).

    The exact same wav file was imported for each of the channels- so it is absolutely identical. Because the LFE track in a dolby playback system (if configred correctly) boosts the LFE by 10db- a correct playback should keep the tone even until it reaches the LFE, where it will jump by several DB (approx 10). If your final tone does not jump obviously- there might be an incorrect setting in your processor.

    2) dd140hz2.wav: A 40hz tone at -20 in the mains/ -30 in the LFE which repeats in each of the 6 channels, 5 seconds a time (Left, Center, Right, Left Surround, Right Surround and LFE).

    The exact same wav file was imported for each of the main channels- so it is absolutely identical (aside from the LFE tone which is 10db down- but all tones were generated using professional tone generation software). Because the LFE track in a dolby playback system (if configred correctly) boosts the LFE by 10db- a correct playback should keep the tone even through all 6 speakers. If the final tone drops off significantly in your system, there is a LFE error.


    -The tone is 40hz sine wave- so for this experiment you will have to have your speakers set to small (the whole point is testing rerouted bass vs lfe!) and you might want to start out with your x-over point around 80, and if you usually run lower- work your way down and see what effect it has.

    - Tones are 5 megs a piece, so broadband is probably a must.

    - These two files are DD encoded wav files. It is possible to burn them to a CD, and play them in a cd player or a dvd player with a digital output- and get DD. This does not work with every player. However- if you have a PC with Spidf output, you should be able to use windows media player to play the files and get DD on your processor (it worked for me with the Maudio Audiophile card). Note, if you try to play these back in the analog domain or if your player can't deal with the format you will get very displeasing noise! Be careful, turn the volume all the way down until the processor confirms a DD lock!

    If anyone has any questions- feel free to post.
     
  2. Vince Maskeeper

    Vince Maskeeper Producer

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    Ok then, guess I overestimated the interest.
     
  3. Kevin C Brown

    Kevin C Brown Producer

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    I'll have to try this. I didn't know you could get a Dolby Digital signal from a CD-R.

    Cool, I had known about that flaw on Avia for ... years. [​IMG] Good to see that others have seen it too.
     
  4. BruceD

    BruceD Screenwriter

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    Vince,

    Do you know of any HT receivers that send both redirected and LFE bass (0.1) to Large mains when they are setup as follows, and don't have the "Both" menu option in the sub setup?

    mains=large
    center and surrounds=small
    sub=yes or sub=no (doesn't matter)

    Does the Dolby document diagram (on Dolby website) for bass management (configuration 2) show this behavior as the standard?
     
  5. Vince Maskeeper

    Vince Maskeeper Producer

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    Bruce,

    To be honest, I dont know what the norm is. I always assumed that if you set LARGE and sub to NO then LFE would go to mains. However, I also assumed if you had sub set to YES, then all LFE would go to the sub.

    Is yours routing some LFE to mains no matter what, when set to large? Or are you looking to buy a model that does this?

    This test tone would be a good way to find out if a product does this: so maybe some of the guys here could try out their config and see if their receivers send some of the LFE tone to the mains if set to large.

    -V
     
  6. BruceD

    BruceD Screenwriter

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    Vince,

    No mine (Panasonic) doesn't send LFE to Large mains when sub=ryes.

    I thought most didn't.

    I've been discussing this with another enthusiast who has a Sony receiver who says he gets LFE from his Large mains regardless if sub=yes or sub=no (and he dosen't have a sub=both).

    I'm guessing the redirected bass from small center and small L&R surrounds adds maybe 3dB each of redirected bass to his Large mains and maybe this is what he thinks is LFE, I don't know.

    The Dolby bass management diagram is a bit unclear actually.
     
  7. ScottCHI

    ScottCHI Screenwriter

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    yeah, i'm involved in this discussion and i still think he's incorrect. that receiver of his should manage bass properly. he needs to turn off/disconnect his sub and repeat his analysis; and just listen next time.

    if he is correct, the only thing i can think that's happening is that the portion of LFE content that's above his crossover setting is being sent to his mains, somehow, and that which is below his xover goes to his sub.
     
  8. Vince Maskeeper

    Vince Maskeeper Producer

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    What test tone is he using? How is he confirming the "LFE" to the mains? Has he tried disconnecting the sub entirely?

    -V
     
  9. BruceD

    BruceD Screenwriter

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    Vince,

    He is using your test tones (as I pointed him to them) and is using his resultant SPL output levels for various configurations to "prove" he is getting LFE from both the Large mains and sub.

    Mains=Large
    center=small
    L&R surrounds=small
    Sub=yes (sub power is turned on or off) and sub=no
    xover 80Hz

    He thinks both redirected and LFE bass are sent to the Large mains (even when sub=yes) and uses the Dolby diagram (config 2 on Dolby website) to support his claim.

    IMO, what he is experiencing is an SPL increase from re-directed bass only (as I indicated above), but since I don't have his Sony receiver I have no way to help him out.
     
  10. BruceD

    BruceD Screenwriter

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    Here is the setup we are discussing that seems to have LFE from mains and sub no matter what the speaker setup for sub is set at (sub=yes or sub=no):

     
  11. Lewis Besze

    Lewis Besze Producer

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    Is the sub hooked up via speaker or line level connection?
     
  12. BruceD

    BruceD Screenwriter

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    Lewis,

    It was connected to the Sony's sub-out, while sub=yes and sub=no was toggled in the speaker setup menu.
     
  13. John Kotches

    John Kotches Cinematographer

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    Vince,

    Patience is a virture. It's the holidays and people (shockingly) might have other things going on [​IMG]

    I just downloaded them and will do some experimenting with them over the next few days.

    Regards,
     

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