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Level meter scales -20dBfs RMS

Posted: Mon Mar 19, 2018 11:23 am
by misjavw
I am calibrating my control room to 79dB for mixing for broadcast. I have the -20dBfs Dolby pink noise file inserted on an audiotrack. (all faders at unity gain). What should my output meters read? The main meter at digital scale reads -8dB peak (orange) and -20dB RMS (yellow). The K-20 Scale meter says +12dB Peak and 0dB RMS. I believe I should use the RMS reading but I am not 100% share. Could anyone shine some light on this matter?


Re: Level meter scales -20dBfs RMS

Posted: Mon Mar 19, 2018 4:01 pm
by MattiasNYC
I think you might be thinking about it the wrong way.

"Short" version:

If you're mixing and want to 'calibrate' for broadcast then measure using broadcast loudness measurements instead of RMS.

So if I were you I would lower the level of that file to -24LKFS (use Control Room metering to measure this) and then just adjust monitoring playback level to where you want it. You should then be able to play back a final mix of something that conforms to -24LKFS broadcast and it should feel appropriate in your room. It won't matter if you read an SPL of 76dB, 79dB or 83dB. It's of no consequence, because your room dimensions and more will determine what is comfortable.

Does that makes sense?

Longer version:

The way I see it is this:

You either have to conform to a monitoring standard or not. For cinema we typically have to in order to know what we're doing. In other words, if we want to use a Dolby format we need both Dolby calibration and Dolby certification. Even without expensive certification calibration according to Dolby specs would be beneficial for cinema.

Now, if you're doing broadcast then we actually don't have a set standard for monitoring. This means that "79dB for mixing for broadcast" is basically an arbitrary number on your part, and so is -20dBFS Dolby pink noise. Those numbers might be close to where you end up, but they aren't set in stone and aren't an actual standard.

The way I approach this is purely practical. I want to calibrate my monitoring environment for two main reasons:

1: So that all speakers output the same level. If they don't my panning would get messed up.

2: So that I can "mix by ear" and get very close to the broadcast loudness specifications I have to comply with.

So with that in mind the way I have done it is basically just grabbing a signal and then measured SPL from each speaker to satisfy my requirement #1. But for #2 - which is what you're attempting - I actually prefer to simply play back a test file at -24LKFS, and I then simply adjust the output until I think it sounds loud enough, a level I would mix at. Once I have done this it means that I can mix by ear to that comfortably loud mix level I like, and it will be very close to -24LKFS.


It's also worth noting that you have both a "reference level" setting and a dim setting in Control Room and they're very, very handy. There are weeks where I have so much work that in order to keep my ears from getting tired I actually mix at a lower level than reference. With Control Room it's very easy to mix at that lower level and with a key-press on my keyboard I'm back to reference, so a quick double-check of levels at reference is super easy.

In other words I can mix comfortably at my home studio and end up close to spec, every single time. I'm typically actually within spec normally, i.e. I hit -24LFKS +/-2dB (for US broadcast). And I have no idea what my SPL is in my room (because I can't remember and don't care).

Re: Level meter scales -20dBfs RMS

Posted: Mon Mar 19, 2018 4:25 pm
by misjavw
Thanks for your elaborate answer. I've been mixing broadcast audio for many years (including remote production) so I am fully aware of the loudness measurements (-24LUFS in The Netherlands). I have no difficulty in mixing and delivery specs.

I was indeed implying to the calibration of my monitor levels, and I was wondering what my output meters should read when playing Pink Noise at -20dBfs. I don't really need my mix room to be calibrated at a specific number of dB's (79 dB SPL), but I was curious about setting this level as a reference. I also have set a reference level in the control room section that is set at a comfortable hearing level, so I am used to that setting.

On the other hand, every now and then I have to mix a commercial or short film for Cinema. So for that I would like to be as calibrated as possible. Even though I don't have a large mixing stage. Our mix room is about 50 m2 with a reasonable amount of acoustic treatment, and Genelec 5.1 monitoring. So setting a good reference level is important, so that my mixes aren't too loud or too soft. I am also familiar with the LEQ loudness standard for cinema trailers and commercials, but for shorts that doesn't apply.

Simply put: What should my Nuendo output meter read when playing -20dB Dolby pink noise? I assume I have to look at the RMS reading (in yellow).


Re: Level meter scales -20dBfs RMS

Posted: Mon Mar 19, 2018 4:48 pm
by MattiasNYC
I guess I'm a bit confused because to me your question is irrelevant. If the file you're playing back is -20dBFS noise (RMS) and that's what you want to use for calibration AND your faders are all at unity, then what does it matter what the meters say? You should be outputting exactly what the file is, which is -20dBFS RMS.

Or are you asking because you're trying to use the meters to confirm the loudness of the output? The screenshots show that the meters are saying the same thing. If you want to confirm the loudness of the file I'd use the offline function for that.

Am I missing something?

(short answer: RMS)

Re: Level meter scales -20dBfs RMS

Posted: Mon Mar 19, 2018 4:59 pm
by misjavw
Yes, I want to make sure that the output level is indeed -20dBFS RMS. Since I've been doing years of (live) broadcast mixing I am used to relying on what my meters are telling me, compared to what I am hearing. The Nuendo meters show two values, RMS and peak. So I guess I've answered the question myself: I should read the RMS value on the meter which indeed says -20dB. I was just al little confused because the (peak) meter says -8dB, so I wasn't sure which part of the meter I should use.

Re: Level meter scales -20dBfs RMS

Posted: Mon Mar 19, 2018 5:05 pm
by MattiasNYC
Ok, got it. I would still probably recommend at least adding a -24LUFS source to your calibration procedure. I find them to be pretty valuable. I think there might be one from AES actually, first a male voice then a female voice..... Anyway...

Re: Level meter scales -20dBfs RMS

Posted: Mon Mar 19, 2018 5:15 pm
by misjavw
Thanks for that advice. I'll have a look at that!

I was also confused because, when you insert the "Testgenerator" plugin (which comes with Nuendo) in a master output insert, set to pink noise at -20dB, the output meter shows -20dB Peak and -30dB RMS (?) When changing it to -10dB the RMS value is -20dB. So I guess the plugin dB gain setting is based on peak values and not on RMS. (Apart from the fact that the generated pink noise is probably not as accurate as the Dolby Pink Noise file)

Re: Level meter scales -20dBfs RMS

Posted: Wed Apr 17, 2019 6:58 pm
by LionHo
Hi...there are a number of terminologies that people try to use to describe a meter which is correctly-calibrated. Some people speak about "sine wave-based" and "square-wave based" calibration, but I find that confusing. Here's how to test if the meter is correct:
Send in a sine wave whose peak level is x. The RMS level in dBFS should read the SAME as the peak. If it reads 3 dB lower, it does not meet the standard.

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