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User17118274845116843363 (Bayview Audio) asked a question.

April 27, 2024 at 5:35 PM
Why doesn't LFE register in the loudness measurement in the Renderer?
Why doesn’t the Renderer measure the loudness of the LFE channel? The momentary reading just stops when only playing something from the LFE? See attached picture. Does that mean anything in the LFE channel does not count towards the -18 LUFS we are supposed to be under for submitting Atmos mixes?
  • 5 answers

  • AdamP (Dolby Labs)

    Hi,

    Yes that is correct. Per the ITU-R BS.1770-4. The low frequency effects (LFE) channel is not included in the measurement. This is part of K-weighting where the LFE content in 5.1 (a 5.1 re-render is used for Atmos loudness measurement) is not deemed relevant to subjective loudness perception.

    If you do a web search for ITU-R BS.1770-4 you can easily pull the full spec. It is a very dense technical document but the first diagram illustrates this.

    Best,
    Adam
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    • User17118274845116843363 (Bayview Audio)

      Thanks. I did discover that the LFE does have an effect on the True Peak measurement. So basically as long as we're under -18 LUFS and -1.0 true peak, anything goes as far as the LFE channel correct?

  • AdamP (Dolby Labs)

    Hi,

    Yes, as far as hitting loudness targets but I'd back away from anything goes. At the risk of stating the obvious, It is still worth being judicious/ aware of some basic LFE guidelines:

    -LFE is included in True Peak (as you noted)
    -the LFE gets dropped from Stereo (but not binaural renders)
    -most consumer systems use bass management
    -duplicating low frequency content in the LFE can result in phase issues with content that is bass managed from the main channels.

    Best,
    Adam
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    • User17118274845116843363 (Bayview Audio)

      For sure! I was aware about what you said about binaural and stereo renders but that never occured to me about duplicating stuff in the LFE that's also in the main being bass managed to the LFE. Probably best if I want something like the low end of a kick in the LFE, then filter that out of your main so the low end is only going to the LFE? Also, side question but what is the point of the stereo render? Is it only if people like the sound of an Atmos mixed dumped down to stereo? I would think most would prefer to use the regular stereo version of a song to listen in stereo.

  • AdamP (Dolby Labs)

    Hi,

    Absolutely on filtering for the LFE.

    One your side question. If there is already an existing stereo mix that make sense. In the big picture - if this is new material it makes sense to mix in Atmos and toggle monitoring in stereo (making downmix and trim selections that work best for the material) and only doing one mix. Killing two birds with one stone. As DAWS like Pro Tools can now monitor Atmos (and stereo) with low latency you can even now start monitoring in Atmos while tracking.

    May not be applicable in all cases at this point but worth keeping in mind with new material.

    Best,
    Adam
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