First FR measurement - where's the zero?

Discussion in 'Measurement Setups, Systems, and Standards' started by Halfwit, Mar 4, 2022.

  1. Halfwit

    Halfwit New

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    This is probably going to sound stupid, but I'm new to this headphone frequency measurement game.

    I just did my first FR headphone measurement. This is the REW graph, which corresponds to what I'm hearing.

    [​IMG]

    However, one thing I don't get, where on the Y-axis (SPL) is "0 dB"? Is that the SPL value REW was showing when I was calibrating the headphones before doing the measurements (84 dB)? Or is some other SPL value considered as "zero", and if so, how to determine it?

    Thank you!
     
  2. Lyander

    Lyander Official SBAF Equitable Empathizer

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    There are two ways to display FR data like this, one where you get decibel values relative to a zero-point and one with "absolute" values in dB (whether dBA or some other weighting). In this case looking for "0dB" doesn't matter much since FR is pretty much relative and the lines will look the same in either instance. There's a setting in REW to change the Y-axis, gonna look it up.

    EDIT: Just click the grey drop down box in the top left next to the Y Axis that currently says "SPL" and select "dBFS" instead.

    Guessing from the look of the 4-5kHz area and the comment about calibrating to 84dB that this is HEQ compensation on MiniDSP EARS? Kinda curious what headphones these are. Audio technica closed backs?

    Also this may be better suited for the all-purpose advice thread:

    https://www.superbestaudiofriends.org/index.php?threads/the-all-purpose-advice-thread.19/unread
     
  3. Halfwit

    Halfwit New

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    Yes, I'm using the MiniDSP EARS and the HEQ compensation.

    When I select the dBFS from the dropdown I just get an empty chart, nothing shows up. I'd like to get the decibel values relative to a zero-point, as that would be easier to interpret for me. At least I think so. Any ideas why I'm not seeing anything after selecting the dBFS from the dropdown menu? What else could I try?
     
  4. purr1n

    purr1n Desire for betterer is endless.

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    I am not familiar with REW. I am assuming you want to normalize, say 500Hz or 1kHz to a 0dbR (relative) level?
     
  5. Biodegraded

    Biodegraded Friend

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    A bit under 66 dB below the bottom of your graph.

    Adjust the Y-axis settings in the 'limits' box (the button with the 4 arrows at top right). If you want to see zero, put 100 at the top and 0 at the bottom. I find it more useful to have a narrower range though, around 50 dB.
     
  6. Halfwit

    Halfwit New

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    It is starting to dawn on me that I've been thinking about this all wrong. I was looking to get a straight line that would go parallel to the X axis and tell me in which parts of the frequency spectrum is the headphone boosted and where it's rolled off. But now I'm starting to realize I can only observe my FR plot as a general overview of the character of my headphones, and can only compare it to plots of other headphones I test by using the same methodology.

    Dunno, I'm confused...
     
  7. Biodegraded

    Biodegraded Friend

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    There's a 'SBAF target' for use with the EARS that you can use to check your headphones against the local version of 'flat'. To get it and for instructions on how to use it, see the README file here:

    https://github.com/superbestaudiofriends/headphone-measurements-frequency-response

    There's some discussion about how it was derived here and more on the compensation and the measurement database here.
     

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