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Document the new EQ and VPC features along with a few loader tunables.

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Reviewed by:	ariff
Approved by:	re (blanket)
This commit is contained in:
Joel Dahl 2009-07-06 19:32:13 +00:00
parent 133898afd5
commit ddbf95702a
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=195417
1 changed files with 56 additions and 5 deletions
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61
share/man/man4/pcm.4
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@ -25,7 +25,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd June 23, 2009
.Dd July 6, 2009
.Dt SOUND 4
.Os
.Sh NAME
@ -141,6 +141,15 @@ 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 EQ
The Parametric Software Equlizer (EQ) enables the use of
.Dq tone
controls (bass and treble).
Commonly used for ear-candy or frequency compensation due to the vast
difference in hardware quality.
EQ is disabled by default, but can be enabled with the
.Va hint.pcm. Ns Ao Ar X Ac Ns Va .eq
tunable.
.Ss VCHANs
Each device can optionally support more playback and recording channels
than physical hardware provides by using
@ -151,15 +160,55 @@ or
options can be configured via the
.Xr sysctl 8
interface but can only be manipulated while the device is inactive.
.Ss VPC
FreeBSD supports independent and individual volume controls for each active
application, without touching the master
.Nm
volume.
This is sometimes referred to as Volume Per Channel (VPC).
The
.Tn VPC
feature is enabled by default.
.Ss Loader Tunables
The following loader tunables are used to set driver configuration at the
.Xr loader 8
prompt before booting the kernel, or they can be stored in
.Pa /boot/loader.conf
in order to automatically set them before booting the kernel.
It is also possible to use
.Xr kenv 1
to change these tunables before loading the
.Nm
driver.
The following tunables can not be changed during runtime using
.Xr sysctl 8 .
.Bl -tag -width indent
.It Va hint.pcm. Ns Ao Ar X Ac Ns Va .eq
Set to 1 or 0 to explicitly enable (1) or disable (0) the equalizer.
Requires a driver reload if changed.
Enabling this will make bass and treble controls appear in mixer applications.
This tunable is undefined by default.
Equalizing is disabled by default.
.It Va hint.pcm. Ns Ao Ar X Ac Ns Va .vpc
Set to 1 or 0 to explicitly enable (1) or disable (0) the
.Tn VPC
feature.
This tunable is undefined by default.
.Tn VPC
is however enabled by default.
.El
.Ss Runtime Configuration
There are a number of
.Xr sysctl 8
variables available.
variables available which can be modified during runtime.
These values can also be stored in
.Pa /etc/sysctl.conf
in order to automatically set them during the boot process.
.Va hw.snd.*
tunables are global settings and
are global settings and
.Va dev.pcm.*
are device specific.
.Bl -tag -width ".Va hw.snd.report_soft_formats" -offset indent
.Bl -tag -width indent
.It Va hw.snd.compat_linux_mmap
Enable to allow PROT_EXEC page mappings.
All Linux applications using sound and
@ -299,7 +348,9 @@ This means that any changes to the volume will be lost.
Enabling this will preserve the volume, at the cost of possible confusion
when applications tries to re-open the same device.
.It Va hw.snd.vpc_mixer_bypass
The recommended way to use the vpc feature is to teach applications to use
The recommended way to use the
.Tn VPC
feature is to teach applications to use
the correct
.Fn ioctl :
.Dv SNDCTL_DSP_GETPLAYVOL, SNDCTL_DSP_SETPLAYVOL,