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diff --git a/doc/filters.texi b/doc/filters.texi index f69ce501b7..8e465ce7e0 100644 --- a/doc/filters.texi +++ b/doc/filters.texi @@ -1267,79 +1267,76 @@ side_right.wav @end example @section compand - Compress or expand audio dynamic range. A description of the accepted options follows. @table @option + @item attacks @item decays -Set list of times in seconds for each channel over which the instantaneous -level of the input signal is averaged to determine its volume. -@option{attacks} refers to increase of volume and @option{decays} refers -to decrease of volume. -For most situations, the attack time (response to the audio getting louder) -should be shorter than the decay time because the human ear is more sensitive -to sudden loud audio than sudden soft audio. -Typical value for attack is @code{0.3} seconds and for decay @code{0.8} -seconds. +Set list of times in seconds for each channel over which the instantaneous level +of the input signal is averaged to determine its volume. @var{attacks} refers to +increase of volume and @var{decays} refers to decrease of volume. For most +situations, the attack time (response to the audio getting louder) should be +shorter than the decay time because the human ear is more sensitive to sudden +loud audio than sudden soft audio. A typical value for attack is 0.3 seconds and +a typical value for decay is 0.8 seconds. @item points -Set list of points for transfer function, specified in dB relative to maximum -possible signal amplitude. -Each key points list need to be defined using the following syntax: -@code{x0/y0 x1/y1 x2/y2 ...}. +Set list of points for the transfer function, specified in dB relative to the +maximum possible signal amplitude. Each key points list must be defined using +the following syntax: @code{x0/y0|x1/y1|x2/y2|....} or +@code{x0/y0 x1/y1 x2/y2 ....} -The input values must be in strictly increasing order but the transfer -function does not have to be monotonically rising. -The point @code{0/0} is assumed but may be overridden (by @code{0/out-dBn}). -Typical values for the transfer function are @code{-70/-70 -60/-20}. +The input values must be in strictly increasing order but the transfer function +does not have to be monotonically rising. The point @code{0/0} is assumed but +may be overridden (by @code{0/out-dBn}). Typical values for the transfer +function are @code{-70/-70|-60/-20}. @item soft-knee -Set amount for which the points at where adjacent line segments on the -transfer function meet will be rounded. Defaults is @code{0.01}. +Set the curve radius in dB for all joints. Defaults to 0.01. @item gain -Set additional gain in dB to be applied at all points on the transfer function -and allows easy adjustment of the overall gain. -Default is @code{0}. +Set additional gain in dB to be applied at all points on the transfer function. +This allows easy adjustment of the overall gain. Defaults to 0. @item volume Set initial volume in dB to be assumed for each channel when filtering starts. -This permits the user to supply a nominal level initially, so that, -for example, a very large gain is not applied to initial signal levels before -the companding has begun to operate. A typical value for audio which is -initially quiet is -90 dB. Default is @code{0}. +This permits the user to supply a nominal level initially, so that, for +example, a very large gain is not applied to initial signal levels before the +companding has begun to operate. A typical value for audio which is initially +quiet is -90 dB. Defaults to 0. @item delay -Set delay in seconds. Default is @code{0}. The input audio -is analysed immediately, but audio is delayed before being fed to the -volume adjuster. Specifying a delay approximately equal to the attack/decay -times allows the filter to effectively operate in predictive rather than -reactive mode. +Set delay in seconds. The input audio is analyzed immediately, but audio is +delayed before being fed to the volume adjuster. Specifying a delay +approximately equal to the attack/decay times allows the filter to effectively +operate in predictive rather than reactive mode. Defaults to 0. + @end table @subsection Examples + @itemize @item -Make music with both quiet and loud passages suitable for listening -in a noisy environment: +Make music with both quiet and loud passages suitable for listening in a noisy +environment: @example -compand=.3 .3:1 1:-90/-60 -60/-40 -40/-30 -20/-20:6:0:-90:0.2 +compand=.3|.3:1|1:-90/-60|-60/-40|-40/-30|-20/-20:6:0:-90:0.2 @end example @item -Noise-gate for when the noise is at a lower level than the signal: +Noise gate for when the noise is at a lower level than the signal: @example -compand=.1 .1:.2 .2:-900/-900 -50.1/-900 -50/-50:.01:0:-90:.1 +compand=.1|.1:.2|.2:-900/-900|-50.1/-900|-50/-50:.01:0:-90:.1 @end example @item -Here is another noise-gate, this time for when the noise is at a higher level +Here is another noise gate, this time for when the noise is at a higher level than the signal (making it, in some ways, similar to squelch): @example -compand=.1 .1:.1 .1:-45.1/-45.1 -45/-900 0/-900:.01:45:-90:.1 +compand=.1|.1:.1|.1:-45.1/-45.1|-45/-900|0/-900:.01:45:-90:.1 @end example @end itemize |