Dynamic range compression

This article describes how to watch movies at night and under poor hearing conditions (noisy environment, weak speakers). At the first sight settings for poor hearing conditions and at night must be different. In the first case we need to make sound louder, and at night we should be quiet. Nevertheless, in both cases we need to do the same. Paradox? Not really...

Poor hearing conditions

Problem: You watch a movie and realize that sound is quiet, so you can hear voices hardly and cannot hear details at all because of environment noise or weak speakers. You try to increase volume, but it does not help because it is already at maximum level.

Enable tray icon and start your movie. AC3Filter's icon will appear at system tray. Click on it and you'll see filter settings dialog.

Take a look on output levels:

You can see that now levels are moving far below maximum level. Let's raise them! To do this, increase Master gain. But keep an eye on levels, it should be no overflows when people speaks (limiting of speech is very noticeable). So it should look like following:

Now speech is reproduced close to the maximum level possible, exactly as we need. Note that levels should not become red on normal sounds, only on loud. AGC must be enabled! Otherwise loud sounds will be clipped that sounds bad.

Different movies may require different gains! For example, one movie may require high gain to watch comfortably, and another will sound badly with this gain due to constant overflow. Therefore you should set high gain with care and decrease it when necessary.

Well voices are good now, but quiet passages are still too quiet and almost inaudible:

In this case DRC can help! DRC gains quiet sounds and does not gain loud. That's what we need, because we don't want voices to be gained anymore to prevent its limiting. Enable DRC and raise DRC level until you can hear quiet sounds more or less clear:

Note, that very high DRC level (above 20dB) may lead to noticeable 'loudness jump' effects (see Loudness and dynamic range). So you should keep balance between loudness of quiet sounds and 'loudness jumps'.

That's all. Now we can hear voices and quiet details clear!

Night watching

Problem: You want to watch a movie at night and do not want to disturb neighbors. So you need to limit loud sounds and decrease overall loudness. But decreasing loudness may force quiet sounds to become inaudible and you want to hear it.

First, we need all loud sounds to be just a little louder than voice, so loud sounds will not make a much of noise. To do this we can make the voice just a little quieter than maximum level, increasing Master gain. This increases loudness? Yes, but we can decrease volume in the media player!

Start a movie, open filter settings and watch output levels. Increase Master gain until output levels raise just below maximum (see screenshots above). Levels should not become red on normal sounds, only on loud. Next, set volume in the player to desired level. That's all. Now loud sound will be just a little louder than voices, and you can set voice level as you want with player's control.

If voice volume is quiet, quiet sounds in the movie may become totally inaudible. To fix this we need to increase loudness of quiet sounds only. That's exactly what DRC does. Enable it and increase DRC level until you can hear quiet sounds.

Good! Now we can hear quiet sounds clear, loud sounds are just a little louder than voice and voice level is freely adjustable with player's control. We reach our goal. Note, that we did exactly the same things as in the first part of the article.