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Replaygain Warning: Normalisation gain would have resulted in clipping
MaxDread
post Feb 7 2014, 13:05
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Hi

I've been doing some ripping with dbPoweramp and noticed things like this in some of the Info Logs:

"FLAC: Warning: Normalisation gain would have resulted in clipping, gain has been reduced to prevent this: Loudness=-17.78LUFS, Gain=-0.22dB, Maximum True Peak=-1.00LUFS, True Peak=0.00LUFS, New gain=-1.00dB [clDSP::EndConversion]"

What exactly does it mean and is it anything to worry about?

I have LUFS set to -18. If the warning message is problematic, then I guess I may have to change it (would prefer not to though)....



Also.....

I'm not totally sure what the RG stats in Audio Properties are telling me. But as an example of a track which just got one of these warnings, the results were:

replaygain_album_gain +0.34 dB
replaygain_album_peak 0.955811
replaygain_track_gain -0.43 dB
replaygain_track_peak 0.936279

I'm most interested to know what the top "+" figure means and whether it is a problem.

But a brief explanation of all the figures would satisfy my inquiring mind!

Many thanks

Max
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ChronoSphere
post Feb 7 2014, 13:28
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I am not sure about the first question, so I'll leave that to someone who knows more.
About the second question, it tells you that
- to keep the relative loudness within the album, this track will have to be made 0.34dB louder
- the album total peak (=loudness of the album overall) is 0.955811
- to meet your target volume, the track will have to be made 0.43dB quieter.
- the maximal loudness within the track is 0.936279

And usually, a small positive gain is fine. You can go to foobar's preferences->playback and set the replay gain behavior to "apply gain and prevent clipping according to peak" to be sure.

This post has been edited by ChronoSphere: Feb 7 2014, 13:30
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MaxDread
post Feb 7 2014, 13:33
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That's really helpful. Thanks for taking the time to explain it. With regard to the 0.955811 / 0.936279 figures, what do they actually mean? What scale are they referring to?

Cheers
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greynol
post Feb 7 2014, 14:32
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Those numbers are peak amplitudes on a linear scale where 1.0 is full-scale.

You were done no favors when one of them was referred to as "maximal loudness".

Provided you use the RG reference of 89, increasing the level by .34 dB will not cause the peak level of .955811 to go over 1.0 (the calculated value is ~0.994). It would take a boost of .393 dB to do that.

Some music (classical, especially) is too dynamic to be raised to an RG reference of 89 dB without clipping. The reference used to be 83 dB which was better suited for more dynamic content.


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mjb2006
post Feb 7 2014, 15:06
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0.955811 = 95.5811% of full scale, a point where the waveform's amplitude is defined to be 0 dB. (0 dBFS; the FS is full scale). Exactly what sample value this is depends on how the values are stored. For 16-bit signed integer samples, an absolute sample value (amplitude) of 32768 is 0 dBFS, and it happens to be a hard limit.

Your album's peak absolute sample value was about 0.955811×32768=31320. 20×log10(0.955811) is the dBFS equivalent: about -0.39 dB. So you can boost the volume by as much as 0.39 dB without clipping.

This post has been edited by mjb2006: Feb 7 2014, 15:08
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2Bdecided
post Feb 7 2014, 15:21
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QUOTE (MaxDread @ Feb 7 2014, 12:05) *
Hi

I've been doing some ripping with dbPoweramp and noticed things like this in some of the Info Logs:

"FLAC: Warning: Normalisation gain would have resulted in clipping, gain has been reduced to prevent this: Loudness=-17.78LUFS, Gain=-0.22dB, Maximum True Peak=-1.00LUFS, True Peak=0.00LUFS, New gain=-1.00dB [clDSP::EndConversion]"

What exactly does it mean and is it anything to worry about?
It's using the EBU R128 calculation instead of the original ReplayGain calculation (which is not a problem), but it's also following the EBU R128 practice of not allowing peaks to hit digital full scale, but keeping them at least 1dB below. As the peak was previously at full scale, and in this case the gain change required to match loudness was not the dominant factor, all that happened was that the gain was reduced by 1dB to meet the EBU R128 "no higher than 1dB below peak" requirement.


Are you applying gain changes to your FLAC files? If so, I wouldn't do that. YMMV.

Cheers,
David.

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Porcus
post Feb 7 2014, 15:57
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QUOTE (2Bdecided @ Feb 7 2014, 15:21) *
Are you applying gain changes to your FLAC files? If so, I wouldn't do that. YMMV.


dBpoweramp has a DSP for RG, and one for RG Apply. Users could choose the wrong one.


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