2 .\" Copyright (c) 2009-2011 Joel Dahl <joel@FreeBSD.org>
3 .\" All rights reserved.
5 .\" Redistribution and use in source and binary forms, with or without
6 .\" modification, are permitted provided that the following conditions
8 .\" 1. Redistributions of source code must retain the above copyright
9 .\" notice, this list of conditions and the following disclaimer.
10 .\" 2. Redistributions in binary form must reproduce the above copyright
11 .\" notice, this list of conditions and the following disclaimer in the
12 .\" documentation and/or other materials provided with the distribution.
14 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
37 PCM audio device infrastructure
39 To compile this driver into the kernel, place the following line in your
40 kernel configuration file:
41 .Bd -ragged -offset indent
47 driver is the main component of the
50 It works in conjunction with a bridge device driver on supported devices
51 and provides PCM audio record and playback once it attaches.
52 Each bridge device driver supports a specific set of audio chipsets and
53 needs to be enabled together with the
56 PCI and ISA PnP audio devices identify themselves so users are usually not
57 required to add anything to
58 .Pa /boot/device.hints .
60 Some of the main features of the
62 driver are: multichannel audio, per-application
63 volume control, dynamic mixing through virtual sound channels, true full
64 duplex operation, bit perfect audio, rate conversion and low latency
69 driver is enabled by default, along with several bridge device drivers.
70 Those not enabled by default can be loaded during runtime with
74 The following bridge device drivers are available:
80 .Xr snd_ai2s 4 (enabled by default on powerpc)
86 .Xr snd_audiocs 4 (enabled by default on sparc64)
94 .Xr snd_davbus 4 (enabled by default on powerpc)
106 .Xr snd_es137x 4 (enabled by default on amd64, i386, sparc64)
114 .Xr snd_hda 4 (enabled by default on amd64, i386)
116 .Xr snd_ich 4 (enabled by default on amd64, i386)
136 .Xr snd_t4dwave 4 (enabled by default on sparc64)
138 .Xr snd_uaudio 4 (enabled by default on amd64, i386, powerpc, sparc64)
140 .Xr snd_via8233 4 (enabled by default on amd64, i386)
147 Refer to the manual page for each bridge device driver for driver specific
148 settings and information.
152 cards, the driver looks for
158 These values can be overridden in
159 .Pa /boot/device.hints .
160 Non-PnP sound cards require the following lines in
162 .Bd -literal -offset indent
166 hint.pcm.0.flags="0x0"
169 Apart from the usual parameters, the flags field is used to specify
172 channel (generally used for capture in full duplex cards).
173 Flags are set to 0 for cards not using a secondary
175 channel, or to 0x10 + C to specify channel C.
177 In general, the module
186 or from the command line using the
189 Options which can be specified in
190 .Pa /boot/loader.conf
192 .Bl -tag -width ".Va snd_driver_load" -offset indent
193 .It Va snd_driver_load
197 this option loads all available drivers.
202 only the Intel High Definition Audio bridge device driver and dependent
203 modules will be loaded.
208 load driver for card/chipset foo.
211 To define default values for the different mixer channels,
212 set the channel to the preferred value using hints, e.g.:
213 .Va hint.pcm.0.line Ns = Ns Qq Li 0 .
214 This will mute the input channel per default.
215 .Ss Multichannel Audio
216 Multichannel audio, popularly referred to as
218 is supported and enabled by default.
219 The FreeBSD multichannel matrix processor supports up to 18 interleaved
220 channels, but the limit is currently set to 8 channels (as commonly used
221 for 7.1 surround sound).
222 The internal matrix mapping can handle reduction, expansion or
223 re-routing of channels.
224 This provides a base interface for related multichannel
227 Multichannel audio works both with and without
230 Most bridge device drivers are still missing multichannel matrixing
231 support, but in most cases this should be trivial to implement.
233 .Va dev.pcm.%d.[play|rec].vchanformat
235 to adjust the number of channels used.
236 The current multichannel interleaved structure and arrangement was
237 implemented by inspecting various popular UNIX applications.
238 There were no single standard, so much care has been taken to try
239 to satisfy each possible scenario, despite the fact that each
240 application has its own conflicting standard.
242 The Parametric Software Equalizer (EQ) enables the use of
244 controls (bass and treble).
245 Commonly used for ear-candy or frequency compensation due to the vast
246 difference in hardware quality.
247 EQ is disabled by default, but can be enabled with the
251 Each device can optionally support more playback and recording channels
252 than physical hardware provides by using
257 options can be configured via the
259 interface but can only be manipulated while the device is inactive.
261 FreeBSD supports independent and individual volume controls for each active
262 application, without touching the master
265 This is sometimes referred to as Volume Per Channel (VPC).
268 feature is enabled by default.
270 The following loader tunables are used to set driver configuration at the
272 prompt before booting the kernel, or they can be stored in
273 .Pa /boot/loader.conf
274 in order to automatically set them before booting the kernel.
275 It is also possible to use
277 to change these tunables before loading the
280 The following tunables can not be changed during runtime using
282 .Bl -tag -width indent
283 .It Va hint.pcm.%d.eq
284 Set to 1 or 0 to explicitly enable (1) or disable (0) the equalizer.
285 Requires a driver reload if changed.
286 Enabling this will make bass and treble controls appear in mixer applications.
287 This tunable is undefined by default.
288 Equalizing is disabled by default.
289 .It Va hint.pcm.%d.vpc
290 Set to 1 or 0 to explicitly enable (1) or disable (0) the
293 This tunable is undefined by default.
295 is however enabled by default.
297 .Ss Runtime Configuration
298 There are a number of
300 variables available which can be modified during runtime.
301 These values can also be stored in
303 in order to automatically set them during the boot process.
305 are global settings and
308 .Bl -tag -width indent
309 .It Va hw.snd.compat_linux_mmap
313 The following values are supported (default is 0):
316 Force disabling/denying PROT_EXEC
320 Auto detect proc/ABI type, allow
322 for Linux applications, and deny for everything else.
324 Always allow PROT_EXEC page mappings.
326 .It Va hw.snd.default_auto
327 Enable to automatically assign default sound unit to the most recent
329 .It Va hw.snd.default_unit
330 Default sound card for systems with multiple sound cards.
333 the default device for
335 Equivalent to a symlink from
338 .Pa /dev/dsp Ns Va ${hw.snd.default_unit} .
339 .It Va hw.snd.feeder_eq_exact_rate
340 Only certain rates are allowed for precise processing.
341 The default behavior is however to allow sloppy processing for all rates,
342 even the unsupported ones.
343 Enable to toggle this requirement and only allow processing for supported
345 .It Va hw.snd.feeder_rate_max
346 Maximum allowable sample rate.
347 .It Va hw.snd.feeder_rate_min
348 Minimum allowable sample rate.
349 .It Va hw.snd.feeder_rate_polyphase_max
350 Adjust to set the maximum number of allowed polyphase entries during the
351 process of building resampling filters.
352 Disabling polyphase resampling has the benefit of reducing memory usage, at
353 the expense of slower and lower quality conversion.
354 Only applicable when the SINC interpolator is used.
355 Default value is 183040.
356 Set to 0 to disable polyphase resampling.
357 .It Va hw.snd.feeder_rate_quality
358 Sample rate converter quality.
359 Default value is 1, linear interpolation.
360 Available options include:
363 Zero Order Hold, ZOH.
364 Very fast, but with poor quality.
366 Linear interpolation.
367 Fast, quality is subject to personal preference.
368 Technically the quality is poor however, due to the lack of anti-aliasing
371 Bandlimited SINC interpolator.
372 Implements polyphase banking to boost the conversion speed, at the cost of
373 memory usage, with multiple high quality polynomial interpolators to improve
374 the conversion accuracy.
375 100% fixed point, 64bit accumulator with 32bit coefficients and high precision
377 Quality values are 100dB stopband, 8 taps and 85% bandwidth.
379 Continuation of the bandlimited SINC interpolator, with 100dB stopband, 36
380 taps and 90% bandwidth as quality values.
382 Continuation of the bandlimited SINC inteprolator, with 100dB stopband, 164
383 taps and 97% bandwidth as quality values.
385 .It Va hw.snd.feeder_rate_round
386 Sample rate rounding threshold, to avoid large prime division at the
388 All requested sample rates will be rounded to the nearest threshold value.
389 Possible values range between 0 (disabled) and 500.
391 .It Va hw.snd.latency
392 Configure the buffering latency.
393 Only affects applications that do not explicitly request
394 blocksize / fragments.
395 This tunable provides finer granularity than the
396 .Va hw.snd.latency_profile
398 Possible values range between 0 (lowest latency) and 10 (highest latency).
399 .It Va hw.snd.latency_profile
400 Define sets of buffering latency conversion tables for the
403 A value of 0 will use a low and aggressive latency profile which can result
404 in possible underruns if the application cannot keep up with a rapid irq
405 rate, especially during high workload.
406 The default value is 1, which is considered a moderate/safe latency profile.
407 .It Va hw.snd.maxautovchans
410 setting that only affects devices with at least one playback or recording channel available.
411 The sound system will dynamically create up to this many
418 Maximum value is 256.
419 .It Va hw.snd.report_soft_formats
420 Controls the internal format conversion if it is
421 available transparently to the application software.
422 When disabled or not available, the application will
423 only be able to select formats the device natively supports.
424 .It Va hw.snd.report_soft_matrix
425 Enable seamless channel matrixing even if the hardware does not support it.
426 Makes it possible to play multichannel streams even with a simple stereo
428 .It Va hw.snd.verbose
429 Level of verbosity for the
432 Higher values include more output and the highest level,
433 four, should be used when reporting problems.
434 Other options include:
437 Installed devices and their allocated bus resources.
439 The number of playback, record, virtual channels, and
442 Channel information per device including the channel's
443 current format, speed, and pseudo device statistics such as
444 buffer overruns and buffer underruns.
446 File names and versions of the currently loaded sound modules.
448 Various messages intended for debugging.
450 .It Va hw.snd.vpc_0db
454 Increase to give more room for attenuation control.
455 Decrease for more amplification, with the possible cost of sound clipping.
456 .It Va hw.snd.vpc_autoreset
457 When a channel is closed the channel volume will be reset to 0db.
458 This means that any changes to the volume will be lost.
459 Enabling this will preserve the volume, at the cost of possible confusion
460 when applications tries to re-open the same device.
461 .It Va hw.snd.vpc_mixer_bypass
462 The recommended way to use the
464 feature is to teach applications to use
467 .Dv SNDCTL_DSP_GETPLAYVOL, SNDCTL_DSP_SETPLAYVOL,
468 .Dv SNDCTL_DSP_SETRECVOL, SNDCTL_DSP_SETRECVOL.
469 This is however not always possible.
470 Enable this to allow applications to use their own existing mixer logic
471 to control their own channel volume.
472 .It Va hw.snd.vpc_reset
473 Enable to restore all channel volumes back to the default value of 0db.
474 .It Va dev.pcm.%d.bitperfect
475 Enable or disable bitperfect mode.
476 When enabled, channels will skip all dsp processing, such as channel
477 matrixing, rate converting and equalizing.
480 stream will be fed directly to the hardware.
483 are enabled, the bitperfect mode will use the
485 format/rate as the definitive format/rate target.
486 The recommended way to use bitperfect mode is to disable
488 and enable this sysctl.
490 .It Va dev.pcm.%d.[play|rec].vchans
491 The current number of
493 allocated per device.
494 This can be set to preallocate a certain number of
496 Setting this value to
501 .It Va dev.pcm.%d.[play|rec].vchanformat
505 All playback paths will be converted to this format before the mixing
507 By default only 2 channels are enabled.
508 Available options include:
513 Stereo, 2 channels (left, right).
515 3 channels (left, right, LFE).
517 3 channels (left, right, rear center).
519 Quadraphonic, 4 channels (front/rear left and right).
521 5 channels (4.0 + LFE).
523 5 channels (4.0 + center).
525 6 channels (4.0 + center + LFE).
527 6 channels (4.0 + front/rear center).
529 7 channels (6.0 + LFE).
531 8 channels (4.0 + center + LFE + left and right side).
533 .It Va dev.pcm.%d.[play|rec].vchanmode
535 format/rate selection.
536 Available options include:
539 Channel mixing is done using fixed format/rate.
540 Advanced operations such as digital passthrough will not work.
541 Can be considered as a
544 This is the default mode for hardware channels which lack support for digital
547 Channel mixing is done using fixed format/rate, but advanced operations such
548 as digital passthrough also work.
549 All channels will produce sound as usual until a digital format playback is
551 When this happens all other channels will be muted and the latest incoming
552 digital format will be allowed to pass through undisturbed.
553 Multiple concurrent digital streams are supported, but the latest stream will
554 take precedence and mute all other streams.
558 mode, but is a bit smarter, especially for
561 channels with different format/rate.
562 When a new channel is about to start, the entire list of virtual channels will
563 be scanned, and the channel with the best format/rate (usually the
564 highest/biggest) will be selected.
565 This ensures that mixing quality depends on the best channel.
566 The downside is that the hardware DMA mode needs to be restarted, which may
567 cause annoying pops or clicks.
569 .It Va dev.pcm.%d.[play|rec].vchanrate
570 Sample rate speed for
573 All playback paths will be converted to this sample rate before the mixing
575 .It Va dev.pcm.%d.polling
576 Experimental polling mode support where the driver operates by querying the
577 device state on each tick using a
580 Disabled by default and currently only available for a few device drivers.
582 .Ss Recording Channels
583 On devices that have more than one recording source (ie: mic and line),
584 there is a corresponding
589 utility can be used to start and stop recording from an specific device.
591 Channel statistics are only kept while the device is open.
592 So with situations involving overruns and underruns, consider the output
593 while the errant application is open and running.
595 The driver supports most of the
598 functions, and most applications work unmodified.
599 A few differences exist, while memory mapped playback is
600 supported natively and in
602 emulation, memory mapped recording is
606 As a consequence, some applications may need to be recompiled
607 with a slightly modified audio module.
610 for a complete list of the supported
616 drivers may create the following
619 .Bl -tag -width ".Pa /dev/audio%d.%d" -compact
620 .It Pa /dev/audio%d.%d
621 Sparc-compatible audio device.
623 Digitized voice device.
624 .It Pa /dev/dspW%d.%d
627 but 16 bits per sample.
628 .It Pa /dev/dsp%d.p%d
630 .It Pa /dev/dsp%d.r%d
632 .It Pa /dev/dsp%d.vp%d
633 Virtual playback channel.
634 .It Pa /dev/dsp%d.vr%d
635 Virtual recording channel.
639 status, including all channels and drivers.
642 The first number in the device node
643 represents the unit number of the
651 Additional messages are sometimes recorded when the
652 device is probed and attached, these messages can be viewed with the
656 The above device nodes are only created on demand through the dynamic
659 Users are strongly discouraged to access them directly.
660 For specific sound card access, please instead use
665 Use the sound metadriver to load all
667 bridge device drivers at once
668 (for example if it is unclear which the correct driver to use is):
670 .Dl kldload snd_driver
672 Load a specific bridge device driver, in this case the Intel
673 High Definition Audio driver:
677 Check the status of all detected
683 Change the default sound device, in this case to the second device.
684 This is handy if there are multiple
688 .Dl sysctl hw.snd.default_unit=1
691 .It pcm%d:play:%d:dsp%d.p%d: play interrupt timeout, channel dead
692 The hardware does not generate interrupts to serve incoming (play)
693 or outgoing (record) data.
694 .It unsupported subdevice XX
695 A device node is not created properly.
728 .Xr snd_via82c686 4 ,
738 .%T "Cookbook formulae for audio EQ biquad filter coefficients, by Robert Bristow-Johnson"
739 .%U "http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt"
742 .%T "Julius O'Smith's Digital Audio Resampling"
743 .%U "http://ccrma.stanford.edu/~jos/resample/"
746 .%T "Polynomial Interpolators for High-Quality Resampling of Oversampled Audio, by Olli Niemitalo"
747 .%U "http://www.student.oulu.fi/~oniemita/dsp/deip.pdf"
751 .%U "http://www.opensound.com/pguide/oss.pdf"
756 device driver first appeared in
767 The API evolved from the VOXWARE
768 standard which later became OSS standard.
771 .An Luigi Rizzo Aq luigi@iet.unipi.it
774 device driver and this manual page.
775 .An Cameron Grant Aq gandalf@vilnya.demon.co.uk
776 later revised the device driver for
778 .An Seigo Tanimura Aq tanimura@r.dl.itc.u-tokyo.ac.jp
779 revised this manual page.
780 It was then rewritten for
783 Some features of your sound card (e.g., global volume control) might not
784 be supported on all devices.