Start documenting some of the new sound stuff. More is on the way.
Probably also needs some more mdoc love. Reviewed by: ariff
This commit is contained in:
Joel Dahl
parent
c9f1e38a85
commit
2014806da9
@ -25,7 +25,7 @@
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.\"
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.\" $FreeBSD$
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.\"
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.Dd June 1, 2009
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.Dd June 22, 2009
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.Dt SOUND 4
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.Os
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.Sh NAME
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@ -178,6 +178,12 @@ Equivalent to a symlink from
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.Pa /dev/dsp
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to
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.Pa /dev/dsp Ns Va ${hw.snd.default_unit} .
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.It Va hw.snd.feeder_eq_exact_rate
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Only certain rates are allowed for precise processing.
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The default behavior is however to allow sloppy processing for all rates,
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even the unsupported ones.
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Enable to toggle this requirement and only allow processing for supported
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rates.
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.It Va hw.snd.feeder_rate_max
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Maximum allowable sample rate.
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.It Va hw.snd.feeder_rate_min
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@ -188,6 +194,40 @@ cost of accuracy.
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All requested sample rates will be rounded to the nearest threshold value.
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Possible values range between 0 (disabled) and 500.
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Default is 25.
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.It Va hw.snd.feeder_polyphase_max
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Adjust to set the maximum number of allowed polyphase entries during the
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process of building resampling filters.
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Only applicable when the SINC interpolator is used.
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Default value is 183040.
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Set to 0 to disable polyphase resampling.
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.It Va hw.snd.feeder_quality
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Sample rate converter quality.
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Default value is 1, linear interpolation.
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Available options include:
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.Bl -tag -width 2n
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.It 0
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Zero Order Hold, ZOH.
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Very fast, but with poor quality.
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.It 1
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Linear interpolation.
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Fast, quality is subject to personal preference.
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Technically the quality is poor however, due to the lack of anti-aliasing
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filtering.
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.It 2
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Bandlimited SINC interpolator.
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Implements polyphase banking to boost the conversion speed, at the cost of
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memory usage, with multiple high quality polynomial interpolators to improve
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the conversion accuracy.
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100% fixed point, 64bit accumulator with 32bit coefficients and high precision
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sample buffering.
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Quality values are 100dB stopband, 8 taps and 85% bandwidth.
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.It 3
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Continuation of the bandlimited SINC interpolator, with 100dB stopband, 36
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taps and 90% bandwidth as quality values.
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.It 4
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Continuation of the bandlimited SINC inteprolator, with 100dB stopband, 164
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taps and 97% bandwidth as quality values.
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.El
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.It Va hw.snd.latency
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Configure the buffering latency.
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Only affects applications that do not explicitly request
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@ -208,7 +248,7 @@ The default value is 1, which is considered a moderate/safe latency profile.
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Global
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.Tn VCHAN
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setting that only affects devices with at least one playback or recording channel available.
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The sound system will dynamically create up this many
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The sound system will dynamically create up to this many
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.Tn VCHANs .
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Set to
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.Dq 0
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@ -221,6 +261,10 @@ Controls the internal format conversion if it is
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available transparently to the application software.
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When disabled or not available, the application will
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only be able to select formats the device natively supports.
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.It Va hw.snd.report_soft_matrix
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Enable seamless channel matrixing even if the hardware does not support it.
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Makes it possible to play multichannel streams even with a simple stereo
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sound card.
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.It Va hw.snd.verbose
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Level of verbosity for the
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.Pa /dev/sndstat
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@ -243,6 +287,38 @@ File names and versions of the currently loaded sound modules.
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.It 4
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Various messages intended for debugging.
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.El
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.It Va hw.snd.vpc_0db
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Default value for pcm volume.
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Increase to give more room for attenuation control.
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Decrease for more amplification, with the possible cost of sound clipping.
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.It Va hw.snd.vpc_autoreset
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When a channel is closed the channel volume will be reset to 0db.
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This means that any changes to the volume will be lost.
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Enabling this will preserve the volume, at the cost of possible confusion
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when applications tries to re-open the same device.
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.It Va hw.snd.vpc_mixer_bypass
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The recommended way to use the vpc feature is to teach applications to use
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the correct ioctl(): SNDCTL_DSP_GETPLAYVOL, SNDCTL_DSP_SETPLAYVOL,
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SNDCTL_DSP_SETRECVOL, SNDCTL_DSP_SETRECVOL.
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This is however not always possible.
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Enable this to allow applications to use their own existing mixer logic
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to control their own channel volume.
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.It Va hw.snd.vpc_reset
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Enable to restore all channel volumes back to the default value of 0db.
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.It Va dev.pcm.%d.bitperfect
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Enable or disable bitperfect mode.
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When enabled, channels will skip all dsp processing, such as channel
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matrixing, rate converting and equalizing.
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The pure pcm stream will be fed directly to the hardware.
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If
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.Tn VCHANs
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are enabled, the bitperfect mode will use the
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.Tn VCHAN
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format/rate as the definitive format/rate target.
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The recommended way to use bitperfect mode is to disable
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.Tn VCHANs
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and enable this sysctl.
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Default is disabled.
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.It Va dev.pcm.%d.[play|rec].vchans
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The current number of
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.Tn VCHANs
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@ -260,6 +336,36 @@ Format for
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mixing.
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All playback paths will be converted to this format before the mixing
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process begins.
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.It Va dev.pcm.%d.[play|rec].vchanmode
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.Tn VCHAN
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format/rate selection.
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Available options include:
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.Bl -tag -width 2n
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.It fixed / 0
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Channel mixing is done using fixed format/rate.
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Advanced operations such as digital passthrough will not work.
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Can be considered as a 'legacy' mode.
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This is the default mode for hardware channels which lack support for digital
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formats.
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.It passthrough / 1
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Channel mixing is done using fixed format/rate, but advanced operations such
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as digital passthrough also works.
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All channels will produce sound as usual until a digital format playback is
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requested.
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When this happens all other channels will be muted and the latest incoming
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digital format will be allowed to pass through undisturbed.
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Multiple concurrent digital streams are supported, but the latest stream will
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take precedence and mute all other streams.
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.It adaptive / 2
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Works like the 'passthrough' mode, but is a bit smarter, especially for
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multiple pcm channels with different format/rate.
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When a new channel is about to start, the entire list of virtual channels will
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be scanned and the channel with the best format/rate (usuallay the
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highest/biggest) will be selected.
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This ensures that mixing quality depends on the best channel.
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The downside is that the hardware DMA mode needs to be restarted, which may
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cause annoying pops or clicks.
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.El
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.It Va dev.pcm.%d.[play|rec].vchanrate
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Sample rate speed for
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.Tn VCHAN
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@ -401,6 +507,14 @@ A device node is not created properly.
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.%T "The OSS API"
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.%O "http://www.opensound.com/pguide/oss.pdf"
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.Re
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.Rs
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.%T "Julius O'Smith's Digital Audio Resampling"
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.%O "http://ccrma.stanford.edu/~jos/resample/"
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.Re
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.Rs
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.%T "Polynomial Interpolators for High-Quality Resampling of Oversampled Audio, by Olli Niemitalo"
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.%O "http://www.student.oulu.fi/~oniemita/dsp/deip.pdf"
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.Re
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.Sh HISTORY
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The
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.Nm
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