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Hello my dear friends,

I'm struggling with this question of not knowing what to do with the ref tone of -20 dBFS on the OMF file. Does this mean that I have to match all the dialogue tracks to this level? There is never, at any point of the post production a normalize of the tracks at any superior level?

Thanks.

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A show usually has a leader reference tone and also has pops, known as sync pops or head pops (versus tail pops) or casually just called "2 pop". The reference tone is in regard to calibration level, the 2 pop is (secondarily for calibration) but primarily for ensuring sync - especially when we';re talking about ProTools sessions containing the complimentary sound assets pertaining to the show. The tail pop is basically the same, but to ensure there is no sync drift, as would happen if an incorrect framerate was utilized or Drop vs No Drop when in 29.97. These get printed to stems and printmasters for the same reason, to ensure sync for layback.

The reference tone of 20dBFS is in reference to the fact that this tone should be pegging the meters at -20dBFS through the entire signal chain, and the mains should calibrated as such that -20dBFS either projects at an equivalent sound level of 85 dBSPL (theatrical dub stage), 82 dBSPL (near/mid-field stage or edit suite), or 78/79 dBSPL (TV sub stage). Really depends upon what work you do. But this reference tone assumes that you have already utilized pink noise with an RTA to calibrate your system to the appropriate SPL reference level across the entire frequency spectrum on the mains. So while pink noise (the Dolby file is the best one out there) is for actually calibrating your mains, the reference tone is for the internal signal flow leading up to the mains. Which, if you pinked correctly, the tone should hit you at an appropriately, but comfortably, present (but not loud) level.

20dBFS also tends to be where the dialogue RMS sits in the mix in a theatrical mix. Peaks of normal dialogue tend to hit around -12dBFS, with loud projections around -6dBFS. But the average energy of your dialogue will sit right in the -20dBFS pocket most of the time. Which, as the reference tone tells you, is an appropriately-present level.

The role of a dialogue EDITOR is to make sense of the OMF and minimally balance the levels "in the ballpark" so that the energy sits in the aforementioned pocket. So in a sense, yes the reference tone is your guide for dialogue levels - but perceptually, NOT literally by the meters. How the reference tone feels perceptually to you, is how the dialogue's presence should also feel perceptually. Mostly, your job here is to edit the material only.

The dialogue MIXER will be taking this balancing out the levels as they should be for a transparent and flowing track.

Let the mixer make the final volume decisions, and don't tie their hands with Normalization, etc. it'll be a waste of your time to do so and you'll be dealing with a less-than-pleasant mixer by locking them into decisions only they are qualified to make.

Hope it helps!

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A reference tone is there for calibrating monitors to ensure that everyone is working at the same volume. -20dBFS indicates that this is American standards, as opposed to British and European standards (-18dBFS). For instructions on speaker calibration see this rather helpful video here: http://vimeo.com/22735507

With regard to the levels you should peak your dialogue to, use a peak program meter (you can find numerous plugins out there which do the trick), and make sure that the peaks fall between 4 and 6. 4 for conversational volumes, 6 for shouty stuff. Make sure nothing peaks above 6 (-10dBFS in the UK, and I'm guessing -12dBFS if you're using US setting - can anyone else help here?)

As for normalisation, if you're doing dialogue editing then you shouldn't worry yourself about that sort of thing - it's above our paygrade! The mixer may change things later on when they start adding in the rest of the soundtrack. Just watch the peaks and keep your dialogue clear crisp and easily understood.

Carlvus

  • You really think that way? Imho, when I edit dialogue I remove any gain variations I can (I even automate if some parts are to silent, esp. if boom operators were not on point) to give the re-recording mixers a good start. I think it makes them happy and it improves my skill set. Win win! – Tobias Schmidt Jan 15 '14 at 10:23
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As Carlvus mentioned, the ref tones purpose is tied to playback level rather than mix levels. If you take my stems with a -20dBFS ref tone to your studio (which I'm assuming would be calibrated), make sure the tones are playing back on your system at -20, and that ensures that you're working with or listening to the mix at the level intended.

The levels of your dialogue have nothing to with the -20dBFS tones, essentially. What you're looking for is the DialNorm, which should be in the specs, to tell you the average level dialogue should be hitting throughout. I've seen this number commonly range around either -24dB or -27 dB, but just get the specs and see.

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dBFS is a decibel scale that uses the maximum possible digital sample value as the reference 0dB (FS is short for "full-scale", and in this scale 0dB represents a hard "peak", instead of a "unity" or "nominal" level as is commonly seen in analog references). Exactly what absolute digital value is used as the reference value for 0dBFS depends on the sample bit size (common ones are 8, 16 and 24 bits per sample) and whether the audio format uses signed or unsigned arithmetic ("zero" could either represent the center point, or the absolute minimum value of a sample representing a "trough" in the waveform). You don't need to know the number value 0dBFS stands for specifically; that's part of the point of using it.

The -20dBFS reference tone is used at the beginning of tracks that have been gain-adjusted or mastered so that the maximum signal level of the rest of the track is right at 0dBFS without exceeding it. As long as the reference tone stays with the track and is never modified or not modified differently from the rest of the track, you can quickly and easily perform any gain adjustments necessary to get the track back to "reference" levels for further work in your DAW. You can also use the same reference tone to gain-balance analog equipment used for playback; 20dB of headroom is a best practice for most analog audio equipment as well (though this varies much more widely among brands and types of equipment)

Similar reference tones can also be used to calibrate the gain structure of your incoming audio interface system, such as a USB microphone preamp, to maximize SNR on both sides of the ADC/DAC and allow you, the recording engineer, to set proper analog gain levels for any real-world source you're plugging into the computer, based on any available level indicator. You can do this calibration by setting up a "loopback" from the line-outs of your interface to the line-ins, playing the tone, setting the head amps on the interface so they're clipping hard (don't have your speakers hooked up or turned on for this), then setting the input level of the computer's recording device so the level is just barely at 0dBFS. Now, if the interface indicates clipping, you're also maxing out the computer, and vice versa.

  • (Mastered/calibrated for 85 dBSPL theatrical, 78 or so SPL for TV such that -20 dBFS = 85 dBSPL = 105 dBSPL max (0dBFS). I respectfuly disagree, Knowing what your dBFS values relate to in SPL is of chief importance, as everything is proportional and open to interpretation. Without following the established FS-to-SPL relationships, everyones levels wold be all over the place. – Stavrosound Jan 24 '14 at 22:06
  • And I must respectfully disagree with you; how loud the monitors are depends on who's mixing, and what. Mastered music tracks are typically ultra-compressed to maintain maximum signal level through most of the track. If you're listening to that through a system calibrated for -20dBFS = 85dBA, you're exposing yourself to 105dBA for however many days your mixdown takes. OSHA mandates hearing protection for workers exposed to that level for longer than 1 hour a day, and that's if they're exposed to no other sounds louder than 85dBA in the same day. It's no wonder sound engineers go deaf. – KeithS Jan 24 '14 at 22:46
  • I still disagree. yes, it depends on who is mixing and what they're mixing (the client), but in post the choices are limited to a few standards - such as 85 and 78/79 SPL. The msuic world is not the same as post, as the OP is discussing. Comparing the two is apples and oranges. Music world is all about pushing to the max, film/TV post is about strict calibration and headroom - not "push it to the max". Again, the OP is discussing Post not Music. – Stavrosound Jan 24 '14 at 22:53
  • Beyond that, people have different perceived levels of volume, and different thresholds of pain. The quoted standard is 130dB; that's the normal threshold for instantaneous perception of pain due to volume (it's also enough to instantly deafen). However, even 95dBA is enough to have people covering their ears after a sufficient time listening to it, and you're asking your sound designers to spend a significant amount of time mixing big sonic effects that will average considerably higher decibel levels than the nominal. – KeithS Jan 24 '14 at 22:53
  • In a film or TV mix, 20dBFS = 85 SPL or 78/79 SPL = unity gain is standard. The max peak is 105 - max peak does not mean sustained. Sustained is roughly 85 (dialogue RMS for theatrical dialnorm). Only for brief periods of time does reach a momentary 105 peak, so a mixer is not exposing themselves to 105 - 105 is just the afforded max of the 20dB headroom to work with. – Stavrosound Jan 24 '14 at 22:56

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