What Audio Level

[peppi_le_piou]

Hi, I am working with avi files. How can I ensure that the audio levels will be the same for every film that I create? When I play them with MPC, WMP, PowerDVD etc they are all a little different in volume. Currently I am going by ear when editing and ensuring that there is no clipping and try to match the level to a retail dvd, but this is still slightly off.

Is there a "standard" in the industry for correct levels so that when it is played on a PC or DVD player the sound level would be the same for all films without having to adjust by a remote control?

How do I achieve this nominal level on a PC? I am using mp3 format.

[yetanotherid]

Most people just normalise the audio track. It's not perfect but there's no perfect method. You could try using Replay Gain. How are you converting the audio to MP3?

Assuming you have the MP3 audio as a separate file you could try MP3Gain (http://mp3gain.sourceforge.net/). It'll analyse the entire audio and adjust it to a set "apparent loudness" without having to re-encode it. It works very well for MP3 music files but movie audio is pretty dynamic.

You can also scan pretty much any audio type for Replay Gain levels so it'd probably be easy enough to scan the original audio track, scan the MP3, and then use something like MP3DirectCut to adjust the MP3 volume accordingly without having to re-encode. I use foobar2000 for that sort of thing (Replay Gain scanning).
Or when you convert the audio can you do so without changing it's volume in the first place.

AC3 audio in DVDs uses a set level for speech and the player adjusts the volume automatically which is supposed to make all DVD audio roughly the same volume but I don't know how easy it'd be to determine the level yourself.

Personally I just normalise and use the remote if necessary after switching to a different movie.

[peppi_le_piou]

Thankyou for the detail, I'll try them out.

[ramicio]

Does anything even recognize tags inside of audio inside containers? I wouldn't think replaygain would work with mp3 embedded in a video container, and also because I don't think any decoder looks for that information.

[yetanotherid]

I wouldn't think replaygain would work with mp3 embedded in a video container, and also because I don't think any decoder looks for that information.

I doubt any players would read ReplayGain tags. You'd have to physically change the volume of the audio track using the ReplayGain information.
Fortunately it can be done losslessly with MP3s and it's fairly easy using MP3Gain. Of course you'd have to demux the audio track, change it's level and remux it back into an AVI. I recall a while ago coming across a program called AVIGain which automates the process, although I've never tried it.

[ramicio]

How is it done losslessly to a lossy track? It can't be done losslessly to anything, but to say changing the volume of a lossy track is lossless is just bonkers. Whenever anything is edited there is a loss of information from quantization. I find the volume knob easy enough adjust.

[setarip_old]

@peppi_le-piou

Hi!When I play them with MPC, WMP, PowerDVD etc they are all a little different in volume. Currently I am going by ear when editing and ensuring that there is no clipping and try to match the level to a retail dvd, but this is still slightly off.

Is there a "standard" in the industry for correct levels so that when it is played on a PC or DVD player the sound level would be the same for all films without having to adjust by a remote control? All of the software players you've mentioned have independent volume controls, so adjust each of them one time to the desired setting...

[J_Darnley]

How is it done losslessly to a lossy track? It can't be done losslessly to anything, but to say changing the volume of a lossy track is lossless is just bonkers. Whenever anything is edited there is a loss of information from quantization. I find the volume knob easy enough adjust.

mp3gain does do the change losslessly because each mp3 frame has a "loudness byte". mp3gain changes these by a constant value which it then saves in an ape tag so you can remove the changes it made.

[ramicio]

Doesn't sound standardized whatsoever...

[Vurbal]

Doesn't sound standardized whatsoever...
The use of APE tags isn't, and although used by default it can be turned off. The normalization itself, using the MP3's Global Gain, certainly is.

[pandy]

http://tech.ebu.ch/docs/r/r128.pdf
http://tech.ebu.ch/webdav/site/tech/shared/techreview/trev_2010-Q3_loudness_Camerer.pdf
http://tech.ebu.ch/docs/tech/tech3342.pdf
http://tech.ebu.ch/docs/techreview/trev_297-spikofski_klar.pdf

[pandy]

gain changing level during decoding (so sample is produced based on compressed data and multiplied by gain factor without touching compressed data) - lossy compression as mp3 act like some special kind of filtering - for some signals sample value can be higher after decoding than 0dBFS - this create serious problem - overloading digital range - http://www.audioholics.com/education/audio-formats-technology/issues-with-0dbfs-levels-on-digital-audio-playback-systems and http://en.wikipedia.org/wiki/DBFS

GAIN can help with this by estimation how big clipping can be and how lower sample value (whole track, album) to common safe value