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Up-to-date documentation:

These filters amplify the audio of the clip by the prescribed amount. You can specify different amount arguments for each channel. If there are more arguments than there are channels, the extra ones are ignored. If there are fewer arguments than channels, the last one is applied to the rest of the channels.

8bit and 24bit audio is converted to float; the other audio formats are kept as they are. See ConvertAudio.


Amplify(clip, float amount [, float amount ]...)

float  amount = 1.0
Multiply (scale) the audio by amount; values are linear :
  • amount > 1.0 increases volume
  • amount < 1.0 decreases volume
  • amount = 1.0 retains the same volume (default)
  • Negative scale factors will shift the phase by 180 degrees (i.e. invert the samples)


AmplifyDB(clip, float amount [, float amount ]...)

float  amount = 0.0
Multiply (scale) the audio by amount; values are in dB (decibels) :
  • amount > 0.0 increases volume
  • amount < 0.0 decreases volume
  • amount = 0.0 retains the same volume (default)

The relation between linear and decibel gain control is:

lin = 10 (dB/20)
dB = 20·log10(lin)

For example,

  • AmplifyDB(  0.0) is equivalent to  Amplify(1.0)  (no change)
  • AmplifyDB(  6.0) is equivalent to  Amplify(2.0)  (about twice as loud)
  • AmplifyDB( -6.0) is equivalent to  Amplify(0.5)  (about half as loud)
  • AmplifyDB( 20.0) is equivalent to  Amplify(10)   (much louder)
  • AmplifyDB(-20.0) is equivalent to  Amplify(0.1)  (much softer)

More examples:

  • AmplifyDB(+3, 0) increases the volume of the left channel by a small amount.
  • Amplify(-1, 1) inverts the phase of the left channel. See Wikipedia: Out Of Phase Stereo.

[edit] See Also

  • Normalize - with show=true, can show the maximum amplification possible without clipping.
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