Open Sound System

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Introduction

The Open Sound System is a commercially-supported sound architecture that works on several UNIX-like and POSIX-compatible systems, including Linux, FreeBSD, Solaris and BeOS/Haiku.

Please note that this article is not about the old OSS, which is included in the Linux kernel sources and is more than 10 years old by now.

This article is about the new OSS versions (often called OSSv4). These versions were previously proprietary - OSS became open source again in July 2007, and is currently available under GPL, BSD or CDDL licenses.

Advantages and disadvantages vs. ALSA

Advantages over ALSA (for users)

  • Includes a transparent software mixer (vmix) in kernel space. This means multiple applications can access the sound device at the same time without problems.
  • The vmix mixer controls allow you to adjust the volume of each application individually.
  • Better support for some sound card models, for example for the Creative X-Fi.
  • Sound quality is usually better.
  • Better support for applications written for the OSS API, of course. The OSS API is widely spread and a lot of applications support it. The ALSA's OSS API emulation, however, is often buggy.

Advantages over ALSA (for developers)

  • Cleaner and easier to use API.
  • API is much better documented.
  • Support for sound drivers in the userspace (oss_userdev).
  • Portability across all supported platforms. If the application works using OSS under Linux, it will work under FreeBSD and Solaris too, for example.
  • Portability across operating systems. It's easier to port OSS to a new operating system.

Disadvantages vs. ALSA

  • USB audio devices support is currently experimental under Linux.
  • Bluetooth audio devices are currently not supported.
  • AC'97 and HDAudio dial-up soft-modems (for example Si3055) are currently not supported.
  • MIDI support is currently not finished. However, you can still use MIDI with a software synthesizer like timidity or fluidsynth.
  • Suspend is currently not supported. You need to unload OSS (by using soundoff) before suspending, and to reload OSS (by using soundon) after resuming.
  • Automatic jack sensing currently doesn't work properly with some HDAudio-powered motherboards. This means that, depending on your motherboard model, you may have to manually switch off your speakers when plugging your earphone.

Installing

  • Install OSS by running:
# pacman -S oss
  • Start OSS by running:
# /etc/rc.d/oss start
  • Add oss to your DAEMONS variable at /etc/rc.conf, so OSS is loaded automatically at each boot.

Note: The above instructions will currently install OSS 4.1. If you want OSS 4.0, you can still find it at AUR.

Testing

  • Test OSS by running:
$ osstest

You should be able to hear music during the test process.

The mixer

The command line mixer is called ossmix. It's very like the BSD audio mixer (mixerctl).

A more friendly, graphical mixer, is available too. It's called ossxmix. It needs the optional depend gtk2 to work.

The ossxmix controls are explained in the following example:

  ______________________________
 / High Definition Audio ALC262 \    ----------------------------------> One tab for each sound card
/________________________________\_______________________________
|
| [x] vmix0-enable [vmix0-rate: 48.000kHz]      vmix0-channels     \     The vmix (virtual mixer) special configurations
|                                               [ Stereo [v] ]      |--> appear at the top. These include sampling rate
|                                                                  /     and mixer priority. They are provided by OSS.
|  __codec1______________________________________________________  
| |  _jack_______________________________________________________  \     
| | |  _int-speaker____________________  __green_________________   |
| | | |                                | |                          |    These are your sound card configurations.
| | | |  _mode______   | |             | |  _mode______   | |       |    Every mixer control that is shown here is
| | | | [ mix   [v] ]  o o [x] [ ]mute | | [ mix   [v] ]  o o [x]   |--> provided by your sound card. Every sound card
| | | |                | |             | |                | |       |    specific control is shown here.
| | | |________________________________| |_______________________   |
| | |____________________________________________________________   |
| |______________________________________________________________  /
|
| ___vmix0_______________________________________________________  \
| |  __mocp___  O O   _firefox_  O O  __pcm7___  O O                |    Here are the vmix mixer controls. These are
| | |         | O O  |         | x x |         | O O                |    virtual mixer controls provided by OSS. Each
| | | | |     | x O  | | |     | x x | | |     | O O                |    slider is the volume control of a different
| | | o o [x] | x x  | o o [x] | x x | o o [x] | O O                |--> application. When one application uses the
| | | | |     | x x  | | |     | x x | | |     | O O                |    sound card, its name is shown in the place of
| | |_________| x x  |_________| x x |_________| O O                |    the 'pcm#' labels. There are also sound level
| |______________________________________________________________   |    meter levels for each application.
|________________________________________________________________  /

Saving and restoring mixer settings

If you wish to save your mixer settings manually, run savemixer. You will require to be a user with write permissions to /usr/lib/oss/etc/save.mixer or you'll need to use the '-f' switch to select another file. savemixer -L restores mixer settings. The init scripts run these commands before shutdown/after starting to keep mixer settings across boot.

savemixer

Configuring Applications for OSS

The best way to make applications only use OSS driver is to recompile this application without ALSA support. These applications often depends on alsa-lib, so find them out, and recompile them.

  • Find the applications depends on alsa-lib:
$ pacman -Qi alsa-lib
  • Search packages end with -oss in AUR. If there are packages you want, download them, and run makepkg
  • If you can not find any, try to download it from ABS, and remove the alsa-lib in depends, and run makepkg and then install it. Don't forget submit and share this package to AUR. :)

Flash plugin

Install the libflashsupport-oss package if you are running Arch i686.

pacman -S libflashsupport-oss

Otherwise, if you are running Arch x86_64, get lib32-libflashsupport-oss from AUR.

Skype

The skype package only includes support for ALSA. To get an OSS-capable Skype, install the skype-oss package from AUR.

KDE Phonon

Pure Qt Phonon should work by default with OSS.

However, if you use KDE, you may have problems if the Xine backend is used for sound output. You can get things working correctly by changing the default Phonon backend.

Edit ~/.kde4/share/config/servicetype_profilerc as follows:

[PhononBackend]
Entry0_Preference=2
Entry0_Service=phononbackends/gstreamer.desktop
Entry1_Preference=1
Entry1_Service=phononbackends/xine.desktop
NumberOfEntries=2

Wine

  • Run winecfg.
winecfg
  • Go to the Audio tab.
  • Select OSS Driver.

Other applications

If you can't get sound from an application not listed here, try looking at the Configuring Applications for OSSv4 page.


Troubleshooting

Troubleshooting HDAudio devices

Understanding why problems arise

If you have a HDAudio sound device, it's very likely that you will have to adjust some mixer settings before your sound works.

HDAudio devices are very powerful in the sense that they can contain a lot of small circuits (called widgets) that can be adjusted by software at any time. These controls are exposed to the mixer, and they can be used, for example, to turn the earphone jack into a sound input jack instead of a sound output jack.

However, there is a side effect, mainly because the HDAudio standard is more flexible than it perhaps should be, and because the vendors often only care to get their official drivers working.

Then, when using HDAudio devices, you often find disorganized mixer controls, that doesn't work at all by default, and you are forced to try every mixer control combination, until it works. You'll probably want to setup a program to record/play continously in the background (e.g. ossrecord - | ossplay - for recording or osstest -lV for playing), while changing mixer settings in ossxmix in the foreground.

How to solve

Open ossxmix and try to change every mixer control in the middle area, that contains the sound card specific controls, as explained in the previous "The mixer" section.

  • Raise every volume control slider.
  • In each option box, try to change the selected option, trying all the possible combinations.
  • If you get noise, try to lower and/or mute some volume controls, until you find the source of the noise.

Please note again that you do not need to change any controls in the top area nor in the bottom area, as they are virtual vmix-related mixer controls.

Troubleshooting other issues

  • If you get distorted sound, try lowering some volume control sliders.
  • If you need to change the default sound card, look at here.
  • If you have another issues, try searching or asking for help at the 4front forums.

Tips and Tricks

Using multimedia keys with OSS

If your multimedia keys don't work by default, read the Using multimedia keys with OSS page.

Other tips

ALSA emulation

Introduction

You can instruct alsa-lib to use OSS as its audio output system. This works as a sort of ALSA emulation.

Note, however, that this method may introduce additional latency in your sound output, and that the emulation is not complete and doesn't work with all applications. It doesn't work, for example, with programs that try to detect devices using ALSA.

So, as most applications support OSS directly, use this method only as a last resort.

In the future, more complete methods may be available for emulating ALSA, such as libsalsa and cuckoo.

HOW-TO

  • Install the alsa-plugins package.
pacman -S alsa-plugins
  • Edit /etc/asound.conf as follows.
pcm.oss {
    type oss
    device /dev/dsp
}

pcm.!default {
    type oss
    device /dev/dsp
}

ctl.oss {
    type oss
    device /dev/mixer
}

ctl.!default {
    type oss
    device /dev/mixer
}