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 26, 2019 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 163.Dx 164multichannel matrix processor supports up to 18 interleaved 165channels, but the limit is currently set to 8 channels (as commonly used 166for 7.1 surround sound). 167The internal matrix mapping can handle reduction, expansion or 168re-routing of channels. 169This provides a base interface for related multichannel 170.Fn ioctl 171support. 172Multichannel audio works both with and without 173.Tn VCHANs . 174.Pp 175Most bridge device drivers are still missing multichannel matrixing 176support, but in most cases this should be trivial to implement. 177Use the 178.Va dev.pcm.%d.[play|rec].vchanformat 179.Xr sysctl 8 180to adjust the number of channels used. 181The current multichannel interleaved structure and arrangement was 182implemented by inspecting various popular UNIX applications. 183There were no single standard, so much care has been taken to try 184to satisfy each possible scenario, despite the fact that each 185application has its own conflicting standard. 186.Ss EQ 187The Parametric Software Equalizer (EQ) enables the use of 188.Dq tone 189controls (bass and treble). 190Commonly used for ear-candy or frequency compensation due to the vast 191difference in hardware quality. 192EQ is disabled by default, but can be enabled with the 193.Va hint.pcm.%d.eq 194tunable. 195.Ss VCHANs 196Each device can optionally support more playback and recording channels 197than physical hardware provides by using 198.Dq virtual channels 199or 200.Tn VCHANs . 201.Tn VCHAN 202options can be configured via the 203.Xr sysctl 8 204interface but can only be manipulated while the device is inactive. 205.Ss VPC 206.Dx 207supports independent and individual volume controls for each active 208application, without touching the master 209.Nm 210volume. 211This is sometimes referred to as Volume Per Channel (VPC). 212The 213.Tn VPC 214feature is enabled by default. 215.Ss Loader Tunables 216The following loader tunables are used to set driver configuration at the 217.Xr loader 8 218prompt before booting the kernel, or they can be stored in 219.Pa /boot/loader.conf 220in order to automatically set them before booting the kernel. 221.\"It is also possible to use 222.\".Xr kenv 1 223.\"to change these tunables before loading the 224.\".Nm 225.\"driver. 226The following tunables can not be changed during runtime using 227.Xr sysctl 8 . 228.Bl -tag -width indent 229.It Va hint.pcm.%d.eq 230Set to 1 or 0 to explicitly enable (1) or disable (0) the equalizer. 231Requires a driver reload if changed. 232Enabling this will make bass and treble controls appear in mixer applications. 233This tunable is undefined by default. 234Equalizing is disabled by default. 235.It Va hint.pcm.%d.vpc 236Set to 1 or 0 to explicitly enable (1) or disable (0) the 237.Tn VPC 238feature. 239This tunable is undefined by default. 240.Tn VPC 241is however enabled by default. 242.El 243.Ss Runtime Configuration 244There are a number of 245.Xr sysctl 8 246variables available which can be modified during runtime. 247These values can also be stored in 248.Pa /etc/sysctl.conf 249in order to automatically set them during the boot process. 250.Va hw.snd.* 251are global settings and 252.Va dev.pcm.* 253are device specific. 254.Bl -tag -width indent 255.It Va hw.snd.compat_linux_mmap 256Linux 257.Xr mmap 2 258compatibility. 259The following values are supported (default is 0): 260.Bl -tag -width 2n 261.It -1 262Force disabling/denying PROT_EXEC 263.Xr mmap 2 264requests. 265.It 0 266Auto detect proc/ABI type, allow 267.Xr mmap 2 268for Linux applications, and deny for everything else. 269.It 1 270Always allow PROT_EXEC page mappings. 271.El 272.It Va hw.snd.default_auto 273Automatically assign the default sound unit. 274The following values are supported (default is 1): 275.Bl -tag -width 2n 276.It 0 277Do not assign the default sound unit automatically. 278.It 1 279Use the best available sound device based on playing and recording 280capabilities of the device. 281.It 2 282Use the most recently attached device. 283.El 284.It Va hw.snd.default_unit 285Default sound card for systems with multiple sound cards. 286When using 287.Xr devfs 5 , 288the default device for 289.Pa /dev/dsp . 290Equivalent to a symlink from 291.Pa /dev/dsp 292to 293.Pa /dev/dsp Ns Va ${hw.snd.default_unit} . 294.It Va hw.snd.feeder_eq_exact_rate 295Only certain rates are allowed for precise processing. 296The default behavior is however to allow sloppy processing for all rates, 297even the unsupported ones. 298Enable to toggle this requirement and only allow processing for supported 299rates. 300.It Va hw.snd.feeder_rate_max 301Maximum allowable sample rate. 302.It Va hw.snd.feeder_rate_min 303Minimum allowable sample rate. 304.It Va hw.snd.feeder_rate_polyphase_max 305Adjust to set the maximum number of allowed polyphase entries during the 306process of building resampling filters. 307Disabling polyphase resampling has the benefit of reducing memory usage, at 308the expense of slower and lower quality conversion. 309Only applicable when the SINC interpolator is used. 310Default value is 183040. 311Set to 0 to disable polyphase resampling. 312.It Va hw.snd.feeder_rate_quality 313Sample rate converter quality. 314Default value is 1, linear interpolation. 315Available options include: 316.Bl -tag -width 2n 317.It 0 318Zero Order Hold, ZOH. 319Very fast, but with poor quality. 320.It 1 321Linear interpolation. 322Fast, quality is subject to personal preference. 323Technically the quality is poor however, due to the lack of anti-aliasing 324filtering. 325.It 2 326Bandlimited SINC interpolator. 327Implements polyphase banking to boost the conversion speed, at the cost of 328memory usage, with multiple high quality polynomial interpolators to improve 329the conversion accuracy. 330100% fixed point, 64bit accumulator with 32bit coefficients and high precision 331sample buffering. 332Quality values are 100dB stopband, 8 taps and 85% bandwidth. 333.It 3 334Continuation of the bandlimited SINC interpolator, with 100dB stopband, 36 335taps and 90% bandwidth as quality values. 336.It 4 337Continuation of the bandlimited SINC interprolator, with 100dB stopband, 164 338taps and 97% bandwidth as quality values. 339.El 340.It Va hw.snd.feeder_rate_round 341Sample rate rounding threshold, to avoid large prime division at the 342cost of accuracy. 343All requested sample rates will be rounded to the nearest threshold value. 344Possible values range between 0 (disabled) and 500. 345Default is 25. 346.It Va hw.snd.latency 347Configure the buffering latency. 348Only affects applications that do not explicitly request 349blocksize / fragments. 350This tunable provides finer granularity than the 351.Va hw.snd.latency_profile 352tunable. 353Possible values range between 0 (lowest latency) and 10 (highest latency). 354.It Va hw.snd.latency_profile 355Define sets of buffering latency conversion tables for the 356.Va hw.snd.latency 357tunable. 358A value of 0 will use a low and aggressive latency profile which can result 359in possible underruns if the application cannot keep up with a rapid irq 360rate, especially during high workload. 361The default value is 1, which is considered a moderate/safe latency profile. 362.It Va hw.snd.maxautovchans 363Global 364.Tn VCHAN 365setting that only affects devices with at least one playback or recording channel available. 366The sound system will dynamically create up to this many 367.Tn VCHANs . 368Set to 369.Dq 0 370if no 371.Tn VCHANs 372are desired. 373Maximum value is 256. 374.It Va hw.snd.report_soft_formats 375Controls the internal format conversion if it is 376available transparently to the application software. 377When disabled or not available, the application will 378only be able to select formats the device natively supports. 379.It Va hw.snd.report_soft_matrix 380Enable seamless channel matrixing even if the hardware does not support it. 381Makes it possible to play multichannel streams even with a simple stereo 382sound card. 383.It Va hw.snd.verbose 384Level of verbosity for the 385.Pa /dev/sndstat 386device. 387Higher values include more output and the highest level, 388four, should be used when reporting problems. 389Other options include: 390.Bl -tag -width 2n 391.It 0 392Installed devices and their allocated bus resources. 393.It 1 394The number of playback, record, virtual channels, and 395flags per device. 396.It 2 397Channel information per device including the channel's 398current format, speed, and pseudo device statistics such as 399buffer overruns and buffer underruns. 400.It 3 401File names and versions of the currently loaded sound modules. 402.It 4 403Various messages intended for debugging. 404.El 405.It Va hw.snd.vpc_0db 406Default value for 407.Nm 408volume. 409Increase to give more room for attenuation control. 410Decrease for more amplification, with the possible cost of sound clipping. 411.It Va hw.snd.vpc_autoreset 412When a channel is closed the channel volume will be reset to 0db. 413This means that any changes to the volume will be lost. 414Enabling this will preserve the volume, at the cost of possible confusion 415when applications tries to re-open the same device. 416.It Va hw.snd.vpc_mixer_bypass 417The recommended way to use the 418.Tn VPC 419feature is to teach applications to use 420the correct 421.Fn ioctl : 422.Dv SNDCTL_DSP_GETPLAYVOL , SNDCTL_DSP_SETPLAYVOL , 423.Dv SNDCTL_DSP_SETRECVOL , SNDCTL_DSP_SETRECVOL . 424This is however not always possible. 425Enable this to allow applications to use their own existing mixer logic 426to control their own channel volume. 427.It Va hw.snd.vpc_reset 428Enable to restore all channel volumes back to the default value of 0db. 429.It Va dev.pcm.%d.bitperfect 430Enable or disable bitperfect mode. 431When enabled, channels will skip all dsp processing, such as channel 432matrixing, rate converting and equalizing. 433The pure 434.Nm 435stream will be fed directly to the hardware. 436If 437.Tn VCHANs 438are enabled, the bitperfect mode will use the 439.Tn VCHAN 440format/rate as the definitive format/rate target. 441The recommended way to use bitperfect mode is to disable 442.Tn VCHANs 443and enable this sysctl. 444Default is disabled. 445.It Va dev.pcm.%d.[play|rec].vchans 446The current number of 447.Tn VCHANs 448allocated per device. 449This can be set to preallocate a certain number of 450.Tn VCHANs . 451Setting this value to 452.Dq 0 453will disable 454.Tn VCHANs 455for this device. 456.It Va dev.pcm.%d.[play|rec].vchanformat 457Format for 458.Tn VCHAN 459mixing. 460All playback paths will be converted to this format before the mixing 461process begins. 462By default only 2 channels are enabled. 463Available options include: 464.Bl -tag -width 2n 465.It s16le:1.0 466Mono. 467.It s16le:2.0 468Stereo, 2 channels (left, right). 469.It s16le:2.1 4703 channels (left, right, LFE). 471.It s16le:3.0 4723 channels (left, right, rear center). 473.It s16le:4.0 474Quadraphonic, 4 channels (front/rear left and right). 475.It s16le:4.1 4765 channels (4.0 + LFE). 477.It s16le:5.0 4785 channels (4.0 + center). 479.It s16le:5.1 4806 channels (4.0 + center + LFE). 481.It s16le:6.0 4826 channels (4.0 + front/rear center). 483.It s16le:6.1 4847 channels (6.0 + LFE). 485.It s16le:7.1 4868 channels (4.0 + center + LFE + left and right side). 487.El 488.It Va dev.pcm.%d.[play|rec].vchanmode 489.Tn VCHAN 490format/rate selection. 491Available options include: 492.Bl -tag -width 2n 493.It fixed 494Channel mixing is done using fixed format/rate. 495Advanced operations such as digital passthrough will not work. 496Can be considered as a 497.Dq legacy 498mode. 499This is the default mode for hardware channels which lack support for digital 500formats. 501.It passthrough 502Channel mixing is done using fixed format/rate, but advanced operations such 503as digital passthrough also work. 504All channels will produce sound as usual until a digital format playback is 505requested. 506When this happens all other channels will be muted and the latest incoming 507digital format will be allowed to pass through undisturbed. 508Multiple concurrent digital streams are supported, but the latest stream will 509take precedence and mute all other streams. 510.It adaptive 511Works like the 512.Dq passthrough 513mode, but is a bit smarter, especially for 514multiple 515.Nm 516channels with different format/rate. 517When a new channel is about to start, the entire list of virtual channels will 518be scanned, and the channel with the best format/rate (usually the 519highest/biggest) will be selected. 520This ensures that mixing quality depends on the best channel. 521The downside is that the hardware DMA mode needs to be restarted, which may 522cause annoying pops or clicks. 523.El 524.It Va dev.pcm.%d.[play|rec].vchanrate 525Sample rate speed for 526.Tn VCHAN 527mixing. 528All playback paths will be converted to this sample rate before the mixing 529process begins. 530.It Va dev.pcm.%d.polling 531Experimental polling mode support where the driver operates by querying the 532device state on each tick using a 533.Xr callout 9 534mechanism. 535Disabled by default and currently only available for a few device drivers. 536.El 537.Ss Recording Channels 538On devices that have more than one recording source (ie: mic and line), 539there is a corresponding 540.Pa /dev/dsp%d.r%d 541device. 542The 543.Xr mixer 8 544utility can be used to start and stop recording from a specific device. 545.Ss Statistics 546Channel statistics are only kept while the device is open. 547So with situations involving overruns and underruns, consider the output 548while the errant application is open and running. 549.Ss IOCTL Support 550The driver supports most of the 551.Tn OSS 552.Fn ioctl 553functions, and most applications work unmodified. 554A few differences exist, while memory mapped playback is 555supported natively, memory mapped recording is not 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