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Old 04-30-2014, 01:01 AM   #1
Shippo
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Default -20dBFS RMS band-limited pink noise download showing as -23 dBFS RMS

Could anyone explain this (please see attached)?

The item playing is downloaded from http://www.digido.com/media/download...2-general.html, and is labelled as -20 dBFS RMS.

However, in both the master track meter and the plugin JS: schwa/audio_statistics the RMS level is about -23 dBFS.

Track and master faders are both at 0.00dB. Applying 3dB gain on the track gives -20 dBFS on the master track.

(The FX on the master track is just another instance of JS: schwa/audio_statistics).
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File Type: jpg Pink Noise.jpg (59.3 KB, 598 views)
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Old 04-30-2014, 01:21 AM   #2
siddhu
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It can have to do with the measurement standard that is being used. Google AES meter standard. You can put the same test tone through different DAWs and meter plug-ins and get different results up to 3 dB.

I know for example that Slate's FG-X gives me a 3dB softer sound than my Brainworx TT Meter plug-in. This has to do with two different standards being used.

Here are my notes on the subject which I found somewhere on the internet (apologies for not being able to credit the original poster/author):


Quote:
"In order to check how the software you're using meters RMS in relation to peak, do the following:
Run a -14dbFS (or any level you want - just make sure this is the peak of the wave) sine wave through the meter and see what it meters. If the result is -14dB then it's sticking to traditional metering; if it's -17dB then it's sticking to the mathematical relationship (without adding 3dB).

Caveat: the meter may not show -14 but show 0 (for example) if you're using some sort of meter scaling, like the K-14 system (in this example).

For example, PSP Xenon, PSP VintageMeter and TT DynamicRange Meter use traditional metering. (RMS = peak for sinewave).

Slate FG-X and T-Racks 3 Metering use the standard math (RMS = peak -3dB for sinewave)
Reaper, Voxengo Elephant and Roger Nichols IXL have the option to offset the meter by +3dB (thus abiding to the traditional standard) or use the mathematic relationship betwen peak and RMS.

An interesting finding is fooBar's ReplayGain and how it works: a 30 second sinewave with a (traditional) RMS of -14 gives a -0.81 gain reduction in foobar. Couldn't figure out why.

In all of the above I assume (and I hope I'm right) the integration time (aka window size) for the RMS is 300 ms; as a sidenote, Reaper and PSP VintageMeter allows one to set the integration time according to his will (amongst other things, like what is 0dB for RMS).

I'm sure Bob Katz could tell us more about this issue."
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Old 04-30-2014, 01:27 AM   #3
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Ah, that explains it!

Thanks, siddhu
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Old 04-30-2014, 01:36 AM   #4
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And to get Reaper to match the measurement standard used on the website, I just need to set 'Display gain' to the 3dB setting in Master VU settings.

It all makes sense!
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Old 04-30-2014, 04:13 AM   #5
planetnine
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AES-17, also known as sinewave calibration.

For a sinewave, the RMS (Root-Mean-Square) value is the peak value divided by the square-root of 2, or about 0.7 time the value. So for 1 volt peak, a sinewave will have an RMS voltage of 0.7 volts, for +6dBu peak an RMS of +3dBu and a -12dBFSD peaking sinewave will have an RMS of -15dBFSD. And for 110Volts RMS electricity, the peak is about 155 volts.

A squarewave, however, has much more area or energy under the waveform trace, and so has a higher RMS value than the sinewave for the same peak value. It is actually equal to the peak value, so for 1Vp it is 1VRMS, for -12dB peak it is -12dB RMS, etc, etc...

This is the way that RMS is calculated, and the way it is used in electrical engineering, telephony, radio wave generation and propagation, etc. It is the calculated RMS value as referred to above.

Traditionally, RMS meters for measuring audio signals have been calibrated with a sinewave so that the RMS reading equals the peak value. This actually makes the meters read a factor of approx 1.4 (root-2, +3dB) of the true RMS value, but as long as all other sound engineers do the same, this is academic and the meters are completely useable and meaningful inside the realms of audio engineering.

This is the method referred to previously as the "Traditional" RMS value. It means squarewaves read at +3dB higher than they should, but squarewaves aren't very musical (mastering engineers and their clients take note!)

This traditional calibration practice has been ratified by the AES and is known as AES17-1998, and most RMS meters for audio either follow this practice or offer it as an option (eg the +3dB option in the REAPER master RMS meter). Those that don't, usually refer to their RMS calibration as "True" RMS, or squarewave calibration.


So, if you want AES-17 RMS readings, check the +3dB box in the master meter options dialogue, but if you want "True" RMS readings, make sure it is unchecked.



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Old 04-30-2014, 08:02 AM   #6
Shippo
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Thanks Nathan.

Wow, it's all a bit complicated isn't it?

There's not much about metering generally in the User Guide, and I feel it would be very useful as there is so much that is non-intuitive.

Is there a procedure for suggested inclusions, anyone?
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Old 04-30-2014, 08:31 AM   #7
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Quote:
Originally Posted by Shippo View Post
Thanks Nathan.

Wow, it's all a bit complicated isn't it?

It doesn't need to be depending... If the file is known to be -20 adjust reapers metering mode to reflect that. Nathan's advice is spot on but you should never need to go to that level just to get the meter to agree unless you want to understand it at that level.
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