自己发在其它地方的，也算转贴吧
我们一直以为AC3的声音小是软件的BUG，但实际上AC3是用在电影院的标准，声音不能太大。用下面的方法提高声音的时候多多少少都有失真。
简单的方法： 在看影片的时候，用Media player 的用户右键点击directvobsub的图标，选AC3Filter,用zoom player的用户右键单击画面 选Filter Properties->AC3filter ，现在会出现AC3Filter的属性，在Main的左下角有一个Preset选项，在下拉的选项中选 loud ,按下确定。现在声音大起来了吧。
复杂一些的方法：
1、在Mixer的页面中把Auto gain control关掉，把Master提高。
缺点：原来声音太强的部分会因为放大后超出正常范围而无法放出，有的比较吵的声音放大后影响声音质量。
2、选中Auto gain control，选中One-pass Normalize，把Master提高。
优点：如果声音太强，之后的声音会减弱，一段时间后音量和音质都达到最好。
缺点：达到稳定的最佳效果需要一段时间。因为太强的声音后音量会减弱，如果为连续的爆炸时，可以防止太吵，但如果爆炸后立刻为对话，则对话会因为声音减弱而听不清，所以想把很小的声音听清楚的目的可能达不到。
3、在第2种方法中不选中One-pass Normalize。
优点：过大的声音去除后Master会恢复，不会出现第二种情况下爆炸后无法听清对话的情况，但对话和爆炸同时出现时会和第二种情况一样无法听清
缺点：使用者必须把握Master提高的幅度，否则声音会忽大忽小。
4、在Main页面中选中Use DRC。
优点：过大的声音会变小，太小的声音会增强。
缺点：声音突然变化的情况会增加
下面是官方网站上对调声音的详细描述：
If it seems that standard settings are too silent it can be fixed. Actually standard settings produce standard output. And any manipulations lead to deviations from standard.
First that should be noted is that most films are normalized to avoid overflows. So if we just raise gain level because sound is too silent at one moment at some other moment overflow may occur.
It is 3 main methods to avoid overflows:
Signal clipping. Signal above maximal level is clipped. It leads to noticeable distortions.
Auto gain control. At overflow gain level automatically decreases. It do not produce noticable distortions but big level jumps may be noticable and annoying.
Dynamic range compression (DRC). It is kind of auto gain control controlled by marks in ac3 stream placed by sound producer.
Simplest method to increase loudness is disable Auto gain control and raise Master gain level. In this case overflows will be clipped. This method increases loudness to the prejudice of quality.
More advanced method is to enable Auto gain control, enable Normalize and raise Master gain level (till maximum level maybe). In this case after overflow gain level will be decreased. After some time gain will almost stop changing. In this case can get maximum loudness with maximum quality. This methods have imperfecttions. First it is some time needed for gain to stabilize. Second, our main goal to clearly hear low-level sound may not be reached. This method may be recommended as quick way to get maximum loudness with minimum artefacts.
As kind of previous method Normalize may be turned off. In this case gain level after overflow will be gradually restored up to Master level. This method is more sensible to choice of Master level. When Master level is too high and it is much of overflows (what is the consequence of high Master level) frequent and sharp gain changes may be annoying. Previous method is devoid of this defect because current gain level is not raising after overflow. But now we can hear low-level sounds (speech for example) after explosions (after some time after it). But speech in between of explosions will be masked agian. This method is recommended for insignificant increase of Master level when it is expected rare overflows or no overflows at all.
Next method is to use dynamic range compression (enable Use DRC option) with Master level raised. Current DRC gain level is shown at respective indicator. At silent scenes it should raise and at loud scenes it should lower. It is possible that effect from DRC is not enough so it is possible to increase effect with DRC level control. It is obvious that 'jumps' of loudness are more noticable with high DRC level. So it should be choosen carefully to make silent sounds clearly audible on the one hand and minimize gain jumps on other hand. In this method gain jumps caused by two reasons: DRC itself and auto gain control. To avoid some gain jumps auto gain can be disabled. But in this case clipping distortions may appear. So it is needed to maintain some kind of balance between all this factors.
Next parameters affect loudness: Master, Auto gain control, Normalize,Use DRC, DRC Level. All this paramteres should be adjusted individually depending on type of acoustics, listener, and movie itself (lazy sound producer forgot to set DRC marks :-).
