Too much gain with normalization.

[Atlantis]

I use normalize in encoding bluray DTS and AC3 to AAC. Don't know if I should do it or not but it always worked without sounding bad.

Recently I did a source and the gain is too high and the resulted audio quality is not too good. Please look at these and the graphs and tell if the normalization is done correctly. Why this happened and why it sounds bad? I never had this much difference after normalization.

command line: eac3to.exe audio.ac3 audio.m4a" -quality=0.4 -normalize -progressnumbers
------------------------------------------------------------------------------
AC3, 2.0 channels, 2:45:58, 192kbps, 48kHz, dialnorm: -27dB
Removing AC3 dialog normalization...
Decoding with libav/ffmpeg...
Writing WAV...
Creating file ...wav"...
Caution: The WAV file is bigger than 4GB. <WARNING>
Some WAV readers might not be able to handle this file correctly. <WARNING>
Starting 2nd pass...
Reading WAV...
Reducing depth from 64 to 32 bits...
Encoding AAC <0.40> with NeroAacEnc...
Applying 6.9dB gain...
Original audio track: max 32 bits, average 30 bits, most common 31 bits.
The processed audio track has a constant bit depth of 32 bits.
eac3to processing took 8 minutes, 25 seconds.
Done.

Before
https://i.postimg.cc/2SVLjGyK/video.jpg

After
https://i.postimg.cc/ZqN9pqrP/video-normalized.jpg

[tebasuna51]

Please look at these and the graphs and tell if the normalization is done correctly...
How we can know with these graphics if the normalization is done correctly?

We can see than frequencies over 16 KHz are discarded because you use a 0.4 quality (use more quality if you want preserve high frequencies, but for my old ears is enough, I can't listen over 12 KHz).

The normalization is correct:
Applying 6.9dB gain...
Is the same than use the volume in your amplifier, don't change the audio quality.

Maybe the source is not good already.

[Atlantis]

So if I normalize it doesn't help in anyway for better hearing dialogs? It's no use?

For what is good normalization in AAC encoding?

[john33]

Normalization affects the volume of the audio, not the quality. If the original audio quality is good, but it is too quiet, than the aac encoder is likely the culprit. There are a number of aac encoders available and they were not created equal, some are good, others are cr4p!

[Richard1485]

So if I normalize it doesn't help in anyway for better hearing dialogs? It's no use?

If you can't hear the dialog because the overall volume level is low, then normalizing in eac3to might help. If you can't hear the dialog because it's low in relation to other elements in the mix, then -normalize in eac3to won't help, and you might look at dynamic audio normalization in ffmpeg (http://ffmpeg.org/ffmpeg-all.html#dynaudnorm).

For what is good normalization in AAC encoding?

Peak normalization can be useful after downmixing, for example.