Start documenting some of the new sound stuff. More is on the way.

Probably also needs some more mdoc love.

Reviewed by:	ariff

1 files changed, 116 insertions, 2 deletions

diff --git a/share/man/man4/pcm.4 b/share/man/man4/pcm.4
index 4fba47d..1aad2e6 100644
--- a/share/man/man4/pcm.4
+++ b/share/man/man4/pcm.4
@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd June 1, 2009
+.Dd June 22, 2009
 .Dt SOUND 4
 .Os
 .Sh NAME
@@ -178,6 +178,12 @@ Equivalent to a symlink from
 .Pa /dev/dsp
 to
 .Pa /dev/dsp Ns Va ${hw.snd.default_unit} .
+.It Va hw.snd.feeder_eq_exact_rate
+Only certain rates are allowed for precise processing.
+The default behavior is however to allow sloppy processing for all rates,
+even the unsupported ones.
+Enable to toggle this requirement and only allow processing for supported
+rates.
 .It Va hw.snd.feeder_rate_max
 Maximum allowable sample rate.
 .It Va hw.snd.feeder_rate_min
@@ -188,6 +194,40 @@ cost of accuracy.
 All requested sample rates will be rounded to the nearest threshold value.
 Possible values range between 0 (disabled) and 500.
 Default is 25.
+.It Va hw.snd.feeder_polyphase_max
+Adjust to set the maximum number of allowed polyphase entries during the
+process of building resampling filters.
+Only applicable when the SINC interpolator is used.
+Default value is 183040.
+Set to 0 to disable polyphase resampling.
+.It Va hw.snd.feeder_quality
+Sample rate converter quality.
+Default value is 1, linear interpolation.
+Available options include:
+.Bl -tag -width 2n
+.It 0
+Zero Order Hold, ZOH.
+Very fast, but with poor quality.
+.It 1
+Linear interpolation.
+Fast, quality is subject to personal preference.
+Technically the quality is poor however, due to the lack of anti-aliasing
+filtering.
+.It 2
+Bandlimited SINC interpolator.
+Implements polyphase banking to boost the conversion speed, at the cost of
+memory usage, with multiple high quality polynomial interpolators to improve
+the conversion accuracy.
+100% fixed point, 64bit accumulator with 32bit coefficients and high precision
+sample buffering.
+Quality values are 100dB stopband, 8 taps and 85% bandwidth.
+.It 3
+Continuation of the bandlimited SINC interpolator, with 100dB stopband, 36
+taps and 90% bandwidth as quality values.
+.It 4
+Continuation of the bandlimited SINC inteprolator, with 100dB stopband, 164
+taps and 97% bandwidth as quality values.
+.El
 .It Va hw.snd.latency
 Configure the buffering latency.
 Only affects applications that do not explicitly request
@@ -208,7 +248,7 @@ The default value is 1, which is considered a moderate/safe latency profile.
 Global
 .Tn VCHAN
 setting that only affects devices with at least one playback or recording channel available.
-The sound system will dynamically create up this many
+The sound system will dynamically create up to this many
 .Tn VCHANs .
 Set to
 .Dq 0
@@ -221,6 +261,10 @@ Controls the internal format conversion if it is
 available transparently to the application software.
 When disabled or not available, the application will
 only be able to select formats the device natively supports.
+.It Va hw.snd.report_soft_matrix
+Enable seamless channel matrixing even if the hardware does not support it.
+Makes it possible to play multichannel streams even with a simple stereo
+sound card.
 .It Va hw.snd.verbose
 Level of verbosity for the
 .Pa /dev/sndstat
@@ -243,6 +287,38 @@ File names and versions of the currently loaded sound modules.
 .It 4
 Various messages intended for debugging.
 .El
+.It Va hw.snd.vpc_0db
+Default value for pcm volume.
+Increase to give more room for attenuation control.
+Decrease for more amplification, with the possible cost of sound clipping.
+.It Va hw.snd.vpc_autoreset
+When a channel is closed the channel volume will be reset to 0db.
+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 correct ioctl(): SNDCTL_DSP_GETPLAYVOL, SNDCTL_DSP_SETPLAYVOL,
+SNDCTL_DSP_SETRECVOL, SNDCTL_DSP_SETRECVOL.
+This is however not always possible.
+Enable this to allow applications to use their own existing mixer logic
+to control their own channel volume.
+.It Va hw.snd.vpc_reset
+Enable to restore all channel volumes back to the default value of 0db.
+.It Va dev.pcm.%d.bitperfect
+Enable or disable bitperfect mode.
+When enabled, channels will skip all dsp processing, such as channel
+matrixing, rate converting and equalizing.
+The pure pcm stream will be fed directly to the hardware.
+If
+.Tn VCHANs
+are enabled, the bitperfect mode will use the
+.Tn VCHAN
+format/rate as the definitive format/rate target.
+The recommended way to use bitperfect mode is to disable
+.Tn VCHANs
+and enable this sysctl.
+Default is disabled.
 .It Va dev.pcm.%d.[play|rec].vchans
 The current number of
 .Tn VCHANs
@@ -260,6 +336,36 @@ Format for
 mixing.
 All playback paths will be converted to this format before the mixing
 process begins.
+.It Va dev.pcm.%d.[play|rec].vchanmode
+.Tn VCHAN
+format/rate selection.
+Available options include:
+.Bl -tag -width 2n
+.It fixed / 0
+Channel mixing is done using fixed format/rate.
+Advanced operations such as digital passthrough will not work.
+Can be considered as a 'legacy' mode.
+This is the default mode for hardware channels which lack support for digital
+formats.
+.It passthrough / 1
+Channel mixing is done using fixed format/rate, but advanced operations such
+as digital passthrough also works.
+All channels will produce sound as usual until a digital format playback is
+requested.
+When this happens all other channels will be muted and the latest incoming
+digital format will be allowed to pass through undisturbed.
+Multiple concurrent digital streams are supported, but the latest stream will
+take precedence and mute all other streams.
+.It adaptive / 2
+Works like the 'passthrough' mode, but is a bit smarter, especially for
+multiple pcm channels with different format/rate.
+When a new channel is about to start, the entire list of virtual channels will
+be scanned and the channel with the best format/rate (usuallay the
+highest/biggest) will be selected.
+This ensures that mixing quality depends on the best channel.
+The downside is that the hardware DMA mode needs to be restarted, which may
+cause annoying pops or clicks.
+.El
 .It Va dev.pcm.%d.[play|rec].vchanrate
 Sample rate speed for
 .Tn VCHAN
@@ -401,6 +507,14 @@ A device node is not created properly.
 .%T "The OSS API"
 .%O "http://www.opensound.com/pguide/oss.pdf"
 .Re
+.Rs
+.%T "Julius O'Smith's Digital Audio Resampling"
+.%O "http://ccrma.stanford.edu/~jos/resample/"
+.Re
+.Rs
+.%T "Polynomial Interpolators for High-Quality Resampling of Oversampled Audio, by Olli Niemitalo"
+.%O "http://www.student.oulu.fi/~oniemita/dsp/deip.pdf"
+.Re
 .Sh HISTORY
 The
 .Nm