1.\" 2.\" Copyright (c) 2009-2011 Joel Dahl <joel@FreeBSD.org> 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 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. 13.\" 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 24.\" SUCH DAMAGE. 25.\" 26.\" $FreeBSD: head/share/man/man4/pcm.4 267938 2014-06-26 21:46:14Z bapt $ 27.\" 28.Dd January 8, 2015 29.Dt SOUND 4 30.Os 31.Sh NAME 32.Nm sound , 33.Nm pcm 34.Nd DragonFly PCM audio device infrastructure 35.Sh SYNOPSIS 36To compile this driver into the kernel, place the following line in your 37kernel configuration file: 38.Bd -ragged -offset indent 39.Cd "device sound" 40.Ed 41.Sh DESCRIPTION 42The 43.Nm 44driver is the main component of the 45.Dx 46sound system. 47It works in conjunction with a bridge device driver on supported devices 48and provides PCM audio record and playback once it attaches. 49Each bridge device driver supports a specific set of audio chipsets and 50needs to be enabled together with the 51.Nm 52driver. 53.Pp 54Some of the main features of the 55.Nm 56driver are: multichannel audio, per-application 57volume control, dynamic mixing through virtual sound channels, true full 58duplex operation, bit perfect audio, rate conversion and low latency 59modes. 60.Pp 61The 62.Nm 63driver is enabled by default, along with several bridge device drivers. 64Those not enabled by default can be loaded during runtime with 65.Xr kldload 8 66or during boot via 67.Xr loader.conf 5 . 68The following bridge device drivers are available: 69.Pp 70.Bl -bullet -compact 71.It 72.Xr snd_als4000 4 73.It 74.Xr snd_atiixp 4 75.It 76.Xr snd_cmi 4 77.It 78.Xr snd_cs4281 4 79.It 80.Xr snd_emu10k1 4 81.It 82.Xr snd_emu10kx 4 83.It 84.Xr snd_envy24 4 85.It 86.Xr snd_envy24ht 4 87.It 88.Xr snd_es137x 4 89.It 90.Xr snd_fm801 4 91.It 92.Xr snd_hda 4 93.It 94.Xr snd_hdspe 4 95.It 96.Xr snd_ich 4 97.It 98.Xr snd_maestro 4 99.It 100.Xr snd_neomagic 4 101.It 102.Xr snd_solo 4 103.It 104.Xr snd_spicds 4 105.It 106.Xr snd_t4dwave 4 107.It 108.Xr snd_uaudio 4 109.It 110.Xr snd_via8233 4 111.It 112.Xr snd_via82c686 4 113.It 114.Xr snd_vibes 4 115.El 116.Pp 117Refer to the manual page for each bridge device driver for driver specific 118settings and information. 119.Ss Boot Variables 120In general, the module 121.Pa snd_foo 122corresponds to 123.Cd "device snd_foo" 124and can be 125loaded by the boot 126.Xr loader 8 127via 128.Xr loader.conf 5 129or from the command line using the 130.Xr kldload 8 131utility. 132Options which can be specified in 133.Pa /boot/loader.conf 134include: 135.Bl -tag -width ".Va snd_driver_load" -offset indent 136.It Va snd_driver_load 137.Pq Dq Li NO 138If set to 139.Dq Li YES , 140this option loads all available drivers. 141.It Va snd_hda_load 142.Pq Dq Li NO 143If set to 144.Dq Li YES , 145only the Intel High Definition Audio bridge device driver and dependent 146modules will be loaded. 147.It Va snd_foo_load 148.Pq Dq Li NO 149If set to 150.Dq Li YES , 151load driver for card/chipset foo. 152.El 153.Pp 154To define default values for the different mixer channels, 155set the channel to the preferred value using hints, e.g.: 156.Va hint.pcm.0.line Ns = Ns Qq Li 0 . 157This will mute the input channel per default. 158.Ss Multichannel Audio 159Multichannel audio, popularly referred to as 160.Dq surround sound 161is supported and enabled by default. 162The FreeBSD multichannel matrix processor supports up to 18 interleaved 163channels, but the limit is currently set to 8 channels (as commonly used 164for 7.1 surround sound). 165The internal matrix mapping can handle reduction, expansion or 166re-routing of channels. 167This provides a base interface for related multichannel 168.Fn ioctl 169support. 170Multichannel audio works both with and without 171.Tn VCHANs . 172.Pp 173Most bridge device drivers are still missing multichannel matrixing 174support, but in most cases this should be trivial to implement. 175Use the 176.Va dev.pcm.%d.[play|rec].vchanformat 177.Xr sysctl 8 178to adjust the number of channels used. 179The current multichannel interleaved structure and arrangement was 180implemented by inspecting various popular UNIX applications. 181There were no single standard, so much care has been taken to try 182to satisfy each possible scenario, despite the fact that each 183application has its own conflicting standard. 184.Ss EQ 185The Parametric Software Equalizer (EQ) enables the use of 186.Dq tone 187controls (bass and treble). 188Commonly used for ear-candy or frequency compensation due to the vast 189difference in hardware quality. 190EQ is disabled by default, but can be enabled with the 191.Va hint.pcm.%d.eq 192tunable. 193.Ss VCHANs 194Each device can optionally support more playback and recording channels 195than physical hardware provides by using 196.Dq virtual channels 197or 198.Tn VCHANs . 199.Tn VCHAN 200options can be configured via the 201.Xr sysctl 8 202interface but can only be manipulated while the device is inactive. 203.Ss VPC 204FreeBSD supports independent and individual volume controls for each active 205application, without touching the master 206.Nm 207volume. 208This is sometimes referred to as Volume Per Channel (VPC). 209The 210.Tn VPC 211feature is enabled by default. 212.Ss Loader Tunables 213The following loader tunables are used to set driver configuration at the 214.Xr loader 8 215prompt before booting the kernel, or they can be stored in 216.Pa /boot/loader.conf 217in order to automatically set them before booting the kernel. 218.\"It is also possible to use 219.\".Xr kenv 1 220.\"to change these tunables before loading the 221.\".Nm 222.\"driver. 223The following tunables can not be changed during runtime using 224.Xr sysctl 8 . 225.Bl -tag -width indent 226.It Va hint.pcm.%d.eq 227Set to 1 or 0 to explicitly enable (1) or disable (0) the equalizer. 228Requires a driver reload if changed. 229Enabling this will make bass and treble controls appear in mixer applications. 230This tunable is undefined by default. 231Equalizing is disabled by default. 232.It Va hint.pcm.%d.vpc 233Set to 1 or 0 to explicitly enable (1) or disable (0) the 234.Tn VPC 235feature. 236This tunable is undefined by default. 237.Tn VPC 238is however enabled by default. 239.El 240.Ss Runtime Configuration 241There are a number of 242.Xr sysctl 8 243variables available which can be modified during runtime. 244These values can also be stored in 245.Pa /etc/sysctl.conf 246in order to automatically set them during the boot process. 247.Va hw.snd.* 248are global settings and 249.Va dev.pcm.* 250are device specific. 251.Bl -tag -width indent 252.It Va hw.snd.compat_linux_mmap 253Linux 254.Xr mmap 2 255compatibility. 256The following values are supported (default is 0): 257.Bl -tag -width 2n 258.It -1 259Force disabling/denying PROT_EXEC 260.Xr mmap 2 261requests. 262.It 0 263Auto detect proc/ABI type, allow 264.Xr mmap 2 265for Linux applications, and deny for everything else. 266.It 1 267Always allow PROT_EXEC page mappings. 268.El 269.It Va hw.snd.default_auto 270Automatically assign the default sound unit. 271The following values are supported (default is 1): 272.Bl -tag -width 2n 273.It 0 274Do not assign the default sound unit automatically. 275.It 1 276Use the best available sound device based on playing and recording 277capabilities of the device. 278.It 2 279Use the most recently attached device. 280.El 281.It Va hw.snd.default_unit 282Default sound card for systems with multiple sound cards. 283When using 284.Xr devfs 5 , 285the default device for 286.Pa /dev/dsp . 287Equivalent to a symlink from 288.Pa /dev/dsp 289to 290.Pa /dev/dsp Ns Va ${hw.snd.default_unit} . 291.It Va hw.snd.feeder_eq_exact_rate 292Only certain rates are allowed for precise processing. 293The default behavior is however to allow sloppy processing for all rates, 294even the unsupported ones. 295Enable to toggle this requirement and only allow processing for supported 296rates. 297.It Va hw.snd.feeder_rate_max 298Maximum allowable sample rate. 299.It Va hw.snd.feeder_rate_min 300Minimum allowable sample rate. 301.It Va hw.snd.feeder_rate_polyphase_max 302Adjust to set the maximum number of allowed polyphase entries during the 303process of building resampling filters. 304Disabling polyphase resampling has the benefit of reducing memory usage, at 305the expense of slower and lower quality conversion. 306Only applicable when the SINC interpolator is used. 307Default value is 183040. 308Set to 0 to disable polyphase resampling. 309.It Va hw.snd.feeder_rate_quality 310Sample rate converter quality. 311Default value is 1, linear interpolation. 312Available options include: 313.Bl -tag -width 2n 314.It 0 315Zero Order Hold, ZOH. 316Very fast, but with poor quality. 317.It 1 318Linear interpolation. 319Fast, quality is subject to personal preference. 320Technically the quality is poor however, due to the lack of anti-aliasing 321filtering. 322.It 2 323Bandlimited SINC interpolator. 324Implements polyphase banking to boost the conversion speed, at the cost of 325memory usage, with multiple high quality polynomial interpolators to improve 326the conversion accuracy. 327100% fixed point, 64bit accumulator with 32bit coefficients and high precision 328sample buffering. 329Quality values are 100dB stopband, 8 taps and 85% bandwidth. 330.It 3 331Continuation of the bandlimited SINC interpolator, with 100dB stopband, 36 332taps and 90% bandwidth as quality values. 333.It 4 334Continuation of the bandlimited SINC interprolator, with 100dB stopband, 164 335taps and 97% bandwidth as quality values. 336.El 337.It Va hw.snd.feeder_rate_round 338Sample rate rounding threshold, to avoid large prime division at the 339cost of accuracy. 340All requested sample rates will be rounded to the nearest threshold value. 341Possible values range between 0 (disabled) and 500. 342Default is 25. 343.It Va hw.snd.latency 344Configure the buffering latency. 345Only affects applications that do not explicitly request 346blocksize / fragments. 347This tunable provides finer granularity than the 348.Va hw.snd.latency_profile 349tunable. 350Possible values range between 0 (lowest latency) and 10 (highest latency). 351.It Va hw.snd.latency_profile 352Define sets of buffering latency conversion tables for the 353.Va hw.snd.latency 354tunable. 355A value of 0 will use a low and aggressive latency profile which can result 356in possible underruns if the application cannot keep up with a rapid irq 357rate, especially during high workload. 358The default value is 1, which is considered a moderate/safe latency profile. 359.It Va hw.snd.maxautovchans 360Global 361.Tn VCHAN 362setting that only affects devices with at least one playback or recording channel available. 363The sound system will dynamically create up to this many 364.Tn VCHANs . 365Set to 366.Dq 0 367if no 368.Tn VCHANs 369are desired. 370Maximum value is 256. 371.It Va hw.snd.report_soft_formats 372Controls the internal format conversion if it is 373available transparently to the application software. 374When disabled or not available, the application will 375only be able to select formats the device natively supports. 376.It Va hw.snd.report_soft_matrix 377Enable seamless channel matrixing even if the hardware does not support it. 378Makes it possible to play multichannel streams even with a simple stereo 379sound card. 380.It Va hw.snd.verbose 381Level of verbosity for the 382.Pa /dev/sndstat 383device. 384Higher values include more output and the highest level, 385four, should be used when reporting problems. 386Other options include: 387.Bl -tag -width 2n 388.It 0 389Installed devices and their allocated bus resources. 390.It 1 391The number of playback, record, virtual channels, and 392flags per device. 393.It 2 394Channel information per device including the channel's 395current format, speed, and pseudo device statistics such as 396buffer overruns and buffer underruns. 397.It 3 398File names and versions of the currently loaded sound modules. 399.It 4 400Various messages intended for debugging. 401.El 402.It Va hw.snd.vpc_0db 403Default value for 404.Nm 405volume. 406Increase to give more room for attenuation control. 407Decrease for more amplification, with the possible cost of sound clipping. 408.It Va hw.snd.vpc_autoreset 409When a channel is closed the channel volume will be reset to 0db. 410This means that any changes to the volume will be lost. 411Enabling this will preserve the volume, at the cost of possible confusion 412when applications tries to re-open the same device. 413.It Va hw.snd.vpc_mixer_bypass 414The recommended way to use the 415.Tn VPC 416feature is to teach applications to use 417the correct 418.Fn ioctl : 419.Dv SNDCTL_DSP_GETPLAYVOL, SNDCTL_DSP_SETPLAYVOL, 420.Dv SNDCTL_DSP_SETRECVOL, SNDCTL_DSP_SETRECVOL. 421This is however not always possible. 422Enable this to allow applications to use their own existing mixer logic 423to control their own channel volume. 424.It Va hw.snd.vpc_reset 425Enable to restore all channel volumes back to the default value of 0db. 426.It Va dev.pcm.%d.bitperfect 427Enable or disable bitperfect mode. 428When enabled, channels will skip all dsp processing, such as channel 429matrixing, rate converting and equalizing. 430The pure 431.Nm 432stream will be fed directly to the hardware. 433If 434.Tn VCHANs 435are enabled, the bitperfect mode will use the 436.Tn VCHAN 437format/rate as the definitive format/rate target. 438The recommended way to use bitperfect mode is to disable 439.Tn VCHANs 440and enable this sysctl. 441Default is disabled. 442.It Va dev.pcm.%d.[play|rec].vchans 443The current number of 444.Tn VCHANs 445allocated per device. 446This can be set to preallocate a certain number of 447.Tn VCHANs . 448Setting this value to 449.Dq 0 450will disable 451.Tn VCHANs 452for this device. 453.It Va dev.pcm.%d.[play|rec].vchanformat 454Format for 455.Tn VCHAN 456mixing. 457All playback paths will be converted to this format before the mixing 458process begins. 459By default only 2 channels are enabled. 460Available options include: 461.Bl -tag -width 2n 462.It s16le:1.0 463Mono. 464.It s16le:2.0 465Stereo, 2 channels (left, right). 466.It s16le:2.1 4673 channels (left, right, LFE). 468.It s16le:3.0 4693 channels (left, right, rear center). 470.It s16le:4.0 471Quadraphonic, 4 channels (front/rear left and right). 472.It s16le:4.1 4735 channels (4.0 + LFE). 474.It s16le:5.0 4755 channels (4.0 + center). 476.It s16le:5.1 4776 channels (4.0 + center + LFE). 478.It s16le:6.0 4796 channels (4.0 + front/rear center). 480.It s16le:6.1 4817 channels (6.0 + LFE). 482.It s16le:7.1 4838 channels (4.0 + center + LFE + left and right side). 484.El 485.It Va dev.pcm.%d.[play|rec].vchanmode 486.Tn VCHAN 487format/rate selection. 488Available options include: 489.Bl -tag -width 2n 490.It fixed 491Channel mixing is done using fixed format/rate. 492Advanced operations such as digital passthrough will not work. 493Can be considered as a 494.Dq legacy 495mode. 496This is the default mode for hardware channels which lack support for digital 497formats. 498.It passthrough 499Channel mixing is done using fixed format/rate, but advanced operations such 500as digital passthrough also work. 501All channels will produce sound as usual until a digital format playback is 502requested. 503When this happens all other channels will be muted and the latest incoming 504digital format will be allowed to pass through undisturbed. 505Multiple concurrent digital streams are supported, but the latest stream will 506take precedence and mute all other streams. 507.It adaptive 508Works like the 509.Dq passthrough 510mode, but is a bit smarter, especially for 511multiple 512.Nm 513channels with different format/rate. 514When a new channel is about to start, the entire list of virtual channels will 515be scanned, and the channel with the best format/rate (usually the 516highest/biggest) will be selected. 517This ensures that mixing quality depends on the best channel. 518The downside is that the hardware DMA mode needs to be restarted, which may 519cause annoying pops or clicks. 520.El 521.It Va dev.pcm.%d.[play|rec].vchanrate 522Sample rate speed for 523.Tn VCHAN 524mixing. 525All playback paths will be converted to this sample rate before the mixing 526process begins. 527.It Va dev.pcm.%d.polling 528Experimental polling mode support where the driver operates by querying the 529device state on each tick using a 530.Xr callout 9 531mechanism. 532Disabled by default and currently only available for a few device drivers. 533.El 534.Ss Recording Channels 535On devices that have more than one recording source (ie: mic and line), 536there is a corresponding 537.Pa /dev/dsp%d.r%d 538device. 539The 540.Xr mixer 8 541utility can be used to start and stop recording from an specific device. 542.Ss Statistics 543Channel statistics are only kept while the device is open. 544So with situations involving overruns and underruns, consider the output 545while the errant application is open and running. 546.Ss IOCTL Support 547The driver supports most of the 548.Tn OSS 549.Fn ioctl 550functions, and most applications work unmodified. 551A few differences exist, while memory mapped playback is 552supported natively and in 553.Tn Linux 554emulation, memory mapped recording is 555not due to 556.Tn VM 557system design. 558As a consequence, some applications may need to be recompiled 559with a slightly modified audio module. 560See 561.In sys/soundcard.h 562for a complete list of the supported 563.Fn ioctl 564functions. 565.Sh FILES 566The 567.Nm 568drivers may create the following 569device nodes: 570.Pp 571.Bl -tag -width ".Pa /dev/audio%d.%d" -compact 572.It Pa /dev/audio%d.%d 573Sparc-compatible audio device. 574.It Pa /dev/dsp%d.%d 575Digitized voice device. 576.It Pa /dev/dspW%d.%d 577Like 578.Pa /dev/dsp , 579but 16 bits per sample. 580.It Pa /dev/dsp%d.p%d 581Playback channel. 582.It Pa /dev/dsp%d.r%d 583Record channel. 584.It Pa /dev/dsp%d.vp%d 585Virtual playback channel. 586.It Pa /dev/dsp%d.vr%d 587Virtual recording channel. 588.It Pa /dev/sndstat 589Current 590.Nm 591status, including all channels and drivers. 592.El 593.Pp 594The first number in the device node 595represents the unit number of the 596.Nm 597device. 598All 599.Nm 600devices are listed 601in 602.Pa /dev/sndstat . 603Additional messages are sometimes recorded when the 604device is probed and attached, these messages can be viewed with the 605.Xr dmesg 8 606utility. 607.Pp 608The above device nodes are only created on demand through the dynamic 609.Xr devfs 5 610clone handler. 611Users are strongly discouraged to access them directly. 612For specific sound card access, please instead use 613.Pa /dev/dsp 614or 615.Pa /dev/dsp%d . 616.Sh EXAMPLES 617Use the sound metadriver to load all 618.Nm 619bridge device drivers at once 620(for example if it is unclear which the correct driver to use is): 621.Pp 622.Dl kldload snd_driver 623.Pp 624Load a specific bridge device driver, in this case the Intel 625High Definition Audio driver: 626.Pp 627.Dl kldload snd_hda 628.Pp 629Check the status of all detected 630.Nm 631devices: 632.Pp 633.Dl cat /dev/sndstat 634.Pp 635Change the default sound device, in this case to the second device. 636This is handy if there are multiple 637.Nm 638devices available: 639.Pp 640.Dl sysctl hw.snd.default_unit=1 641.Sh DIAGNOSTICS 642.Bl -diag 643.It pcm%d:play:%d:dsp%d.p%d: play interrupt timeout, channel dead 644The hardware does not generate interrupts to serve incoming (play) 645or outgoing (record) data. 646.It unsupported subdevice XX 647A device node is not created properly. 648.El 649.Sh SEE ALSO 650.Xr snd_als4000 4 , 651.Xr snd_atiixp 4 , 652.Xr snd_cmi 4 , 653.Xr snd_cs4281 4 , 654.Xr snd_emu10k1 4 , 655.Xr snd_emu10kx 4 , 656.Xr snd_envy24 4 , 657.Xr snd_envy24ht 4 , 658.Xr snd_es137x 4 , 659.Xr snd_fm801 4 , 660.Xr snd_hda 4 , 661.Xr snd_hdspe 4 , 662.Xr snd_ich 4 , 663.Xr snd_maestro 4 , 664.Xr snd_neomagic 4 , 665.Xr snd_solo 4 , 666.Xr snd_spicds 4 , 667.Xr snd_t4dwave 4 , 668.Xr snd_uaudio 4 , 669.Xr snd_via8233 4 , 670.Xr snd_via82c686 4 , 671.Xr snd_vibes 4 , 672.Xr devfs 5 , 673.Xr loader.conf 5 , 674.Xr dmesg 8 , 675.Xr kldload 8 , 676.Xr mixer 8 , 677.Xr sysctl 8 678.Rs 679.%T "Cookbook formulae for audio EQ biquad filter coefficients, by Robert Bristow-Johnson" 680.%O "http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt" 681.Re 682.Rs 683.%T "Julius O'Smith's Digital Audio Resampling" 684.%O "http://ccrma.stanford.edu/~jos/resample/" 685.Re 686.Rs 687.%T "Polynomial Interpolators for High-Quality Resampling of Oversampled Audio, by Olli Niemitalo" 688.%O "http://www.student.oulu.fi/~oniemita/dsp/deip.pdf" 689.Re 690.Rs 691.%T "The OSS API" 692.%O "http://www.opensound.com/pguide/oss.pdf" 693.Re 694.Sh HISTORY 695The 696.Nm 697device driver first appeared in 698.Fx 2.2.6 699as 700.Nm pcm , 701written by 702.An Luigi Rizzo . 703It was later 704rewritten in 705.Fx 4.0 706by 707.An Cameron Grant . 708The API evolved from the VOXWARE 709standard which later became OSS standard. 710.Sh AUTHORS 711.An -nosplit 712.An Luigi Rizzo Aq Mt luigi@iet.unipi.it 713initially wrote the 714.Nm pcm 715device driver and this manual page. 716.An Cameron Grant Aq Mt gandalf@vilnya.demon.co.uk 717later revised the device driver for 718.Fx 4.0 . 719.An Seigo Tanimura Aq Mt tanimura@r.dl.itc.u-tokyo.ac.jp 720revised this manual page. 721It was then rewritten for 722.Fx 5.2 . 723.Sh BUGS 724Some features of your sound card (e.g., global volume control) might not 725be supported on all devices. 726