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Document the new multichannel support.

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Reviewed by:	ariff
Approved by:	re (blanket)
This commit is contained in:
joel 2009-07-11 15:25:13 +00:00
parent 8424d74020
commit 8ba6464b3d
1 changed files with 51 additions and 1 deletions
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52
share/man/man4/pcm.4
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@ -25,7 +25,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd July 9, 2009
.Dd July 11, 2009
.Dt SOUND 4
.Os
.Sh NAME
@ -141,6 +141,30 @@ To define default values for the different mixer channels,
set the channel to the preferred value using hints, e.g.:
.Va hint.pcm.0.line Ns = Ns Qq Li 0 .
This will mute the input channel per default.
.Ss Multichannel Audio
Multichannel audio, popularly referred to as
.Dq surround sound
is supported and enabled by default.
The FreeBSD multichannel matrix processor supports up to 18 interleaved
channels, but the limit is currently set to 8 channels (known as 7.1).
The internal matrix mapping can handle reduction, expansion or
re-routing of channels.
This provides a base interface for related multichannel
.Fn ioctl
support.
Works with or without
.Tn VCHANs .
Most bridge device drivers are still missing multichannel matrixing support
, but in most cases this should be trivial to implement.
Use the
.Va dev.pcm.%d.[play|rec].vchanformat
.Xr sysctl(8)
to adjust the number of channels used.
The current multichannel interleaved structure and arrangement was
implemented by inspecting various popular UNIX applications.
There were no single standard, so much care has been taken to try
to satisfy each possible scenario, despite the fact that each
application has its own conflicting standard.
.Ss EQ
The Parametric Software Equlizer (EQ) enables the use of
.Dq tone
@ -407,6 +431,32 @@ Format for
mixing.
All playback paths will be converted to this format before the mixing
process begins.
By default only 2 channels are enabled.
Available options include:
.Bl -tag -width 2n
.It s16le:1.0
Mono
.It s16le:2.0
Stereo, 2 channels, (left, right).
.It s16le:2.1
3 channels (left, right, LFE).
.It s16le:3.0
3 channels (left, right, rear center).
.It s16le:4.0
Quadraphonic, 4 channels (front/rear left and right).
.It s16le:4.1
5 channels (4.0 + LFE).
.It s16le:5.0
5 channels (4.0 + center).
.It s16le:5.1
6 channels (4.0 + center + LFE).
.It s16le:6.0
6 channels (4.0 + front/rear center).
.It s16le:6.1
7 channels (6.0 + LFE).
.It s16le:7.1
8 channels (4.0 + center + LFE + left and right side).
.El
.It Va dev.pcm.%d.[play|rec].vchanmode
.Tn VCHAN
format/rate selection.