AC3 stereo audio track from DVD has very low/quiet sound

[LaLunaDelCielo]

Here is the MediaInfo log for the AC3 2.0 track. How can I fix the audio without re-encoding? It seems like the issue with the low/very quiet sounds stems from all these -31 dB/-11.02 dB values. I also included a sample of the AC3 file.

Audio
ID : 189 (0xBD)-128 (0x80)
Format : AC-3
Format/Info : Audio Coding 3
Commercial name : Dolby Digital
Muxing mode : DVD-Video
Duration : 1 h 18 min
Bit rate mode : Constant
Bit rate : 192 kb/s
Channel(s) : 2 channels
Channel layout : L R
Sampling rate : 48.0 kHz
Frame rate : 31.250 FPS (1536 SPF)
Compression mode : Lossy
Stream size : 78.7 KiB (0%)
Service kind : Complete Main
bsid : 4
Dialog Normalization : -31
Dialog Normalization : -31 dB
compr : -11.02
compr : -11.02 dB
dsurmod : 0
acmod : 2
lfeon : 0
dialnorm_Average : -31
dialnorm_Average : -31 dB
dialnorm_Minimum : -31
dialnorm_Minimum : -31 dB
dialnorm_Maximum : -31
dialnorm_Maximum : -31 dB
dialnorm_Count : 1824
compr_Average : -11.02
compr_Average : -11.02 dB
compr_Minimum : -11.02
compr_Minimum : -11.02 dB
compr_Maximum : -11.02
compr_Maximum : -11.02 dB
compr_Count : 1824
Source : VTS_01_1.VOB

[davexnet]

You can modify the Dialnorm setting without re-encoding by using CHANGEDN
For example, set it to a louder value such as -10
https://forum.doom9.org/showthread.php?p=1493146#post1493146

[LaLunaDelCielo]

You can modify the Dialnorm setting without re-encoding by using CHANGEDN
For example, set it to a louder value such as -10
https://forum.doom9.org/showthread.php?p=1493146#post1493146

I tried ChangeDN and set the DN value to 10 and audio is just as low/quiet as before so it didn't fix the issue unfortunately.

Stream size                    : 13.7 MiB (100%)
Service kind                   : Complete Main
Dialog Normalization           : -10 dB
compr                          : -11.02 dB
dialnorm_Average               : -10 dB
dialnorm_Minimum               : -10 dB
dialnorm_Maximum               : -10 dB

[davexnet]

Is this file the same as your result or different? dialnorm is set to 5 but this time the file is re-encoded

[LaLunaDelCielo]

This re-encoded ac3 file sounds the same as my modified ac3 file using ChangeDN.

Edit: I re-encoded my original ac3 file from my first comment using this command and now the audio is fine:

ffmpeg -i input.ac3 -af "volume=21.74dB" -c:a ac3 -b:a 192k output.ac3

MediaInfo fields now look like this:

Compression mode               : Lossy
Stream size                    : 13.7 MiB (100%)
Service kind                   : Complete Main
Dialog Normalization           : -31 dB
dialnorm_Average               : -31 dB
dialnorm_Minimum               : -31 dB
dialnorm_Maximum               : -31 dB

Would be nice to achieve the same result without having to re-encode the ac3 file, is it possible?

[davexnet]

This re-encoded ac3 file sounds the same as my modified ac3 file using ChangeDN.

Makes sense - some playback chains will respect dialnorm and some will ignore it (It's metadata)
if you play it back in Audacity (that respects the dialnorm) it is louder, as shown by my graphic above ( the wavform is wider)
where your original file is at the bottom and dialnorm 5 file is at the top.

[timtape]

Compressed audio does most damage to quiet audio. If you raise gain appropriately before re encoding, the re encoded version is unlikely to sound appreciably worse. If you can, re encode to a high bitrate.