avfilter: add agate filter

Signed-off-by: Paul B Mahol <onemda@gmail.com>

1 files changed, 51 insertions, 0 deletions

diff --git a/doc/filters.texi b/doc/filters.texi
index 5bbbaf0b78..5b00eca19f 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -641,6 +641,57 @@ Force the output to either unsigned 8-bit or signed 16-bit stereo
 aformat=sample_fmts=u8|s16:channel_layouts=stereo
 @end example
 
+@section agate
+
+A gate is mainly used to reduce lower parts of a signal. This kind of signal
+processing reduces disturbing noise between useful signals.
+
+Gating is done by detecting the volume below a chosen level @var{threshold}
+and divide it by the factor set with @var{ratio}. The bottom of the noise
+floor is set via @var{range}. Because an exact manipulation of the signal
+would cause distortion of the waveform the reduction can be levelled over
+time. This is done by setting @var{attack} and @var{release}.
+
+@var{attack} determines how long the signal has to fall below the threshold
+before any reduction will occur and @var{release} sets the time the signal
+has to raise above the threshold to reduce the reduction again.
+Shorter signals than the chosen attack time will be left untouched.
+
+@table @option
+@item level_in
+Set input level before filtering.
+
+@item range
+Set the level of gain reduction when the signal is below the threshold.
+
+@item threshold
+If a signal rises above this level the gain reduction is released.
+
+@item ratio
+Set a ratio about which the signal is reduced.
+
+@item attack
+Amount of milliseconds the signal has to rise above the threshold before gain
+reduction stops.
+
+@item release
+Amount of milliseconds the signal has to fall below the threshold before the
+reduction is increased again.
+
+@item makeup
+Set amount of amplification of signal after processing.
+
+@item knee
+Curve the sharp knee around the threshold to enter gain reduction more softly.
+
+@item detection
+Choose if exact signal should be taken for detection or an RMS like one.
+
+@item link
+Choose if the average level between all channels or the louder channel affects
+the reduction.
+@end table
+
 @section alimiter
 
 The limiter prevents input signal from raising over a desired threshold.