4.3. Software Volume adjustment
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## 4.3. Software Volume adjustment

Some audio tracks are too quiet to be heard comfortably without amplification. This becomes a problem when your audio equipment cannot amplify the signal for you. The `-softvol` option directs MPlayer to use an internal mixer. You can then use the volume adjustment keys (by default 9 and 0) to reach much higher volume levels. Note that this does not bypass your sound card's mixer; MPlayer only amplifies the signal before sending it to your sound card. The following example is a good start:

    mplayer quiet-file -softvol -softvol-max 300

The `-softvol-max` option specifies the maximum allowable output volume as a percentage of the original volume. For example, `-softvol-max 200` would allow the volume to be adjusted up to twice its original level. It is safe to specify a large value with `-softvol-max`; the higher volume will not be used until you use the volume adjustment keys. The only disadvantage of a large value is that, since MPlayer adjusts volume by a percentage of the maximum, you will not have as precise control when using the volume adjustment keys. Use a lower value with `-softvol-max` and/or specify `-volstep 1` if you need higher precision.

The `-softvol` option works by controlling the `volume` audio filter. If you want to play a file at a certain volume from the beginning you can specify `volume` manually:

    mplayer quiet-file -af volume=10

This will play the file with a ten decibel gain. Be careful when using the `volume` filter - you could easily hurt your ears if you use too high a value. Start low and work your way up gradually until you get a feel for how much adjustment is required. Also, if you specify excessively high values, `volume` may need to clip the signal to avoid sending your sound card data that is outside the allowable range; this will result in distorted audio.

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4.2. Channel manipulation | 起始页 | 第 5 章 CD/DVD用法