avfilter: add chorus filter

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

1 files changed, 55 insertions, 0 deletions

diff --git a/doc/filters.texi b/doc/filters.texi
index b33379d08a..0f2e720df0 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -1320,6 +1320,61 @@ front_center.wav -map '[LFE]' lfe.wav -map '[SL]' side_left.wav -map '[SR]'
 side_right.wav
 @end example
 
+@section chorus
+Add a chorus effect to the audio.
+
+Can make a single vocal sound like a chorus, but can also be applied to instrumentation.
+
+Chorus resembles an echo effect with a short delay, but whereas with echo the delay is
+constant, with chorus, it is varied using using sinusoidal or triangular modulation.
+The modulation depth defines the range the modulated delay is played before or after
+the delay. Hence the delayed sound will sound slower or faster, that is the delayed
+sound tuned around the original one, like in a chorus where some vocals are slightly
+off key.
+
+It accepts the following parameters:
+@table @option
+@item in_gain
+Set input gain. Default is 0.4.
+
+@item out_gain
+Set output gain. Default is 0.4.
+
+@item delays
+Set delays. A typical delay is around 40ms to 60ms.
+
+@item decays
+Set decays.
+
+@item speeds
+Set speeds.
+
+@item depths
+Set depths.
+@end table
+
+@subsection Examples
+
+@itemize
+@item
+A single delay:
+@example
+chorus=0.7:0.9:55:0.4:0.25:2
+@end example
+
+@item
+Two delays:
+@example
+chorus=0.6:0.9:50|60:0.4|0.32:0.25|0.4:2|1.3
+@end example
+
+@item
+Fuller sounding chorus with three delays:
+@example
+chorus=0.5:0.9:50|60|40:0.4|0.32|0.3:0.25|0.4|0.3:2|2.3|1.3
+@end example
+@end itemize
+
 @section compand
 Compress or expand the audio's dynamic range.