svn commit: r195619 - head/share/man/man4

[Ben Kaduk]

On Sat, Jul 11, 2009 at 11:25 AM, Joel Dahl<joel at freebsd.org> wrote:
> Author: joel (doc committer)
> Date: Sat Jul 11 15:25:13 2009
> New Revision: 195619
> URL: http://svn.freebsd.org/changeset/base/195619
>
> Log:
>  Document the new multichannel support.
>
>  Reviewed by:  ariff
>  Approved by:  re (blanket)
>
> Modified:
>  head/share/man/man4/pcm.4
>
> Modified: head/share/man/man4/pcm.4
> ==============================================================================
> --- head/share/man/man4/pcm.4   Sat Jul 11 15:02:45 2009        (r195618)
> +++ head/share/man/man4/pcm.4   Sat Jul 11 15:25:13 2009        (r195619)
> @@ -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 differe
>  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 expression "known as 7.1" is a bit odd.  Maybe "as commonly
used for 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 .


This sentence has no subject.  Is the intent to say "multichannel
audio works with both software VCHANs and hardware channels"?


> +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)

Pedantically, this is a sysctl node, though the meaning is probably
clear enough with the current text.


> +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).

The second comma is probably spurious (cf. quadrophonic, below).

> +.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 would be nice to be consistent about using "and", "+"
or neither for the parentheticals.
Also, "LFE" does not appear to be expanded to "low frequency
enhancement" anywhere ....


Documentation nits aside, I'm really glad to have this audio work
hit the tree -- my primary audio setup is currently based on a
box running -current.

-Ben Kaduk