Jump to content

# Open Sound System

From ArchWiki

Related articles

- Advanced Linux Sound Architecture#OSS emulation

The Open Sound System (OSS) was the original sound system for Linux.

It was superseded by the Advanced Linux Sound Architecture (ALSA), which has a number of advantages over OSS:

- Better support for USB audio devices.
  - OSS has experimental output support for USB audio devices, but no input.
- Support for Bluetooth audio devices.
- Support for AC'97 and HD Audio dial-up softmodems.
- Better support for MIDI devices.
  - OSS supports MIDI devices with the help of a software synthesizer such as Timidity or FluidSynth.
- Support for suspend.
- Better support for jack detection.

## Installation

Install the ossAUR package, or the package with non-free drivers oss-nonfreeAUR.

This will install the OSS, run the OSS install script (temporarily disabling the ALSA modules) and install the OSS kernel modules. Since ALSA is enabled by default, you need to disable it so it does not conflict with OSS. You can do this by blacklisting the `soundcore` module.

After blacklisting the module, you can enable `oss.service` to start at boot.

To start using OSS without needing to reboot, check if any ALSA modules are still loaded (ALSA modules start with "snd"):

    # lsmod | grep snd

Remove the ALSA modules as follows:

    # lsmod | awk ' { print $1 } ' | grep snd | xargs rmmod

Then restart OSS:

    # soundoff && soundon

To completely remove ALSA from your system, you can compile a custom kernel and disable ALSA in its configuration. See Gentoo:ALSA#Kernel for the details.

Note When uninstalling PulseAudio and ALSA, there is more than one package to remove. Search for "pulse" and "alsa" in your installed packages.

This article or section is out of date.

Reason: This should be the same as for ALSA, i.e. not recommended by default. See Advanced_Linux_Sound_Architecture#User_privileges. (Discuss in Talk:Open Sound System)

In case you are not part of the audio group, add yourself and relogin for the changes to take effect:

    # gpasswd -a $USER audio

In case OSS is not able to detect your card when starting it, run:

    # ossdetect -v
    # soundoff && soundon

## Testing

Warning The default volume is very loud, avoid using earphones and physically lower the volume of your speakers (if possible) before running the test.

Test OSS by running:

    $ osstest

You should be able to hear music during the test process. If there is no audio, try to adjust the volume or refer to the #Troubleshooting section.

If you want to hear sounds from more than one application simultaneously, you need `vmix`, OSS's software mixer.

Check that vmix is enabled by running:

    $ ossmix -a | grep -i vmix

You should see a line like `vmix0-enable ON|OFF (currently ON)`. If you do not see any lines beginning with `vmix`, it probably means that `vmix` has not been attached to your sound device. To attach `vmix`, issue the command:

    $ vmixctl attach device

where device is your sound device, e.g. `/dev/oss/oss_envy240/pcm0`.

To avoid having to issue this command manually in the future, you can add it to `/usr/lib/oss/soundon.user`, as suggested by the official documentation.

If you get a `"Device or resource busy"` error, you need to add `vmix_no_autoattach=1` to `/usr/lib/oss/conf/osscore.conf` and then reboot.

See which devices are detected by running:

    $ ossinfo

You should be able to see your devices listed under Device Objects or Audio Devices. If the device that you want to use is not at the top of one of these sections, you have to edit `/usr/lib/oss/etc/installed_drivers` and place the driver for your device at the very top. It may be required to restart OSS:

    # soundoff && soundon

If this does not work, comment all drivers listed except the ones for your device.

## Volume control mixer

To control the volume of various devices, mixers levels will need to be set. There are two mixers:

ossmix
  a command-line mixer, similar to the BSD audio mixer `mixerctl`.
ossxmix
  a GTK-based graphical mixer.

### Color definitions

For high definition (HD) audio, `ossxmix` will color jack configurations by their pre-defined jack colors:

Color | Type | Connector
--- | --- | ---
green | front channels (stereo output) | 3.5mm TRS
black | rear channels (stereo output) | 3.5mm TRS
grey | side channels (stereo output) | 3.5mm TRS
gold | center and subwoofer (dual output) | 3.5mm TRS
blue | line level (stereo input) | 3.5mm TRS
pink | microphone (mono input) | 3.5mm TS

### Saving mixer levels

Mixer levels are saved when you shut off your computer. If you want to save the mixer level immediately, execute as root:

    # savemixer

`savemixer` can be used to write mixer levels to a file with the `-f` switch and restore by the `-L` switch.

### Other mixers

Other mixers that have support for OSS:

- Gnome Volume Control — for GNOME.

  https://help.gnome.org/users/gnome-volume-control/stable/ || gnome

- Kmix — for KDE.

  https://www.kde.org/applications/multimedia/kmix/ || kmix

## Configuring applications for OSS

Tip See also Advanced Linux Sound Architecture#OSS emulation.

### GStreamer-based

If you have problems with applications that use GStreamer for audio, you can try removing pulseaudio and installing the gst-plugins-good package which is needed by `oss4sink` and `oss4src`.

### OpenAL-based

By default OpenAL uses ALSA. To change this, simply define the usage of OSS in `/etc/openal/alsound.conf`:

    /etc/openal/alsound.conf

    drivers=oss

### Audacity

If Audacity starts, but it complains that it cannot open the device or simply does not play anything, then you may be using `vmix` which prevents Audacity from having exclusive access to your sound device. To fix this, before running Audacity, run:

    $ ossmix vmix0-enable OFF

You can restore `vmix` after closing Audacity with:

    $ ossmix vmix0-enable ON

### Gajim

By default, Gajim uses `aplay -q` to play a sound. For OSS you can change it to the equivalent `ossplay -qq` by going to Edit > Preferences > Advanced, opening the Advanced Configuration Editor and modifying the `soundplayer` variable accordingly.

### MOC

To use MOC with OSS v4.1 you must change `OSSMixerDevice` to `/dev/ossmix` in your configuration file (located in `~/.moc`). For issues with the interface try changing the `OSSMixerChannel` by pressing `w` in `mocp` (to change to the sofware mixer).

### MPD

MPD is configured through `/etc/mpd.conf` or `~/.mpdconf`. Check both of these files, looking for something that looks like:

    /etc/mpd.conf

    ...
    audio_output {
        type    "alsa"
        name    "Some Device Name"
    }
    ...

If you find an uncommented (the lines do not begin with #'s) ALSA configuration like the one above, comment all of it out, or delete it, and add the following:

    /etc/mpd.conf

    ...
    audio_output {
        type    "oss"
        name    "My OSS Device"
    }
    ...

Further configuration might not be necessary for all users. However, if you experience issues (in that MPD does not work properly after it has been restarted), or if you like having specific (i.e. more user-configured, less auto-configured) configuration files, the audio output for OSS can be more specifically configured by finding the card identifier:

    $ ossinfo | grep /dev/dsp

Look for the line that says something similar to `/dev/dsp -> /dev/oss/CARD_IDENTIFIER/pcm0`. Take note of what your `CARD_IDENTIFIER` is, and add these lines to your OSS `audio_output` in your MPD configuration file:

    /etc/mpd.conf

    ...
    audio_output {
        type            "oss"
        name            "My OSS Device"
        device          "/dev/oss/<SOME_CARD_IDENTIFIER>/pcm0"
        mixer_device    "/dev/oss/<SOME_CARD_IDENTIFIER>/mix0"
    }
    ...

See also: Music Player Daemon#System-wide configuration.

### MPlayer

If you are using a GUI (SMplayer, GNOME MPlayer, etc.) you can select OSS as the default output in the settings dialogs. If you use MPlayer from the command-line, you should specify the sound output:

    $ mplayer -ao oss /some/file/to/play.mkv

If you do not want to bother typing it over and over again add `ao=oss` to your configuration file (at `~/.mplayer/config`).

See also: MPlayer#Configuration.

### VLC media player

You can select OSS as the default output in the audio settings.

### Wine

To set OSS support in Wine start:

    $ winecfg

and go to the `Audio` tab and select the `OSS Driver`.

See also: Wine#Sound.

### Other applications

- If you can not get sound from an application not listed here, try looking at the Configuring Applications for OSSv4 page.
- Search for OSS specific packages with pacman or by looking in the AUR.

See also: ossapps.

## Tips and tricks

### More convenient and precise volume control

This article or section is a candidate for merging with #Keyboard volume control.

Notes: This partially replaces the existing section without much added value, they can probably be presented as equivalent options in the same section instead of two different ones. (Discuss in Talk:Open Sound System)

The volume lever of ossxmix is very small, making it difficult to finely control the volume.

Run `ossmix` to find the control you want to control (refer to `ossxmix`), this example is `codec1.jack.green.front`.

Bind the following commands to the keyboard shortcuts of the desktop environment.

Increase the volume by 1 (the volume can be between 0 and 100):

    $ ossmix codec1.jack.green.front +1

Decrease the volume by 1 (The `--` is needed on some systems so that the `-1` will not be mistaken for a parameter.):

    $ ossmix -- codec1.jack.green.front -1

Then you can easily control the volume.

### Keyboard volume control

An easy way to mute/unmute and increase/decrease the volume is to use the ossvol script.

Download the script and place it at `/usr/bin/ossvol`.

Once you installed it, type:

    $ ossvol -t

to toggle mute, or:

    $ ossvol -h

to see the available commands.

Note If `ossvol` gives an error like Bad mixer control name(987) 'vol', you need to edit the script and change the `CHANNEL` variable to your default channel (usually `vmix0-outvol`).

If you want to use multimedia keys with `ossvol`, map the following commands to your volume keys: `XF86AudioRaiseVolume`, `XF86AudioLowerVolume` and `XF86AudioMute`:

To mute/unmute the volume:

    $ ossvol -t

To lower the volume:

    $ ossvol -d 2

To raise the volume:

    $ ossvol -i 2

### Changing the sample rate

Changing the output sample rate is not obvious at first. Sample rates can only be changed by root and `vmix` must be unused by any programs when a change is requested. Before you follow any of these steps, ensure you are going through a receiver/amplifier and using quality speakers and not simply computer speakers. If you are only using computer speakers, do not bother changing anything here as you will not notice a difference.

By default the sample rate is 48000hz. There are several conditions in which you may want to change this. This all depends on your usage patterns. You want the sample rate you are using to match the media you use the most. If your computer has to change the sampling rate of the media to suit the hardware it is likely, though not guaranteed, that you will have a loss in audio quality. This is most noticeable in down sampling (ie. 96000hz → 48000hz). There is an article about this issue in Stereophile which was discussed on Apple's CoreAudio API mailing list if you wish to learn more about this issue.

This article or section is out of date.

Reason: Intel HD Audio was released in 2004, most motherboards provide it now. (Discuss in Talk:Open Sound System)

Some example sample rates:

44100hz
  Sample rate of standard Red Book audio CDs.
88000hz
  Sample rate of SACD high definition audio discs/downloads. It is rare that your motherboard will support this sample rate.
96000hz
  Sample rate of most high definition audio downloads. If your motherboard is an AC'97 motherboard, this is likely to be your highest bitrate.
192000hz
  Sample rate of BluRay, and some (very few) high definition downloads. Support for external audio receiver equipment is limited to high end audio. Not all motherboards support this. An example of a motherboard chipset that would support this includes HD Audio.

To check what your sample rate is currently set to, run:

    $ ossmix | grep rate

You are likely to see `vmix0-rate <decimal value> (currently 48000) (Read-only)`.

This article or section is out of date.

Reason: The carve-out for Envy24 was probably relevant in 2003, but we're 20 years later… (Discuss in Talk:Open Sound System)

If you do not see a `vmix0-rate` (or `vmix1-rate`, etc.) being outputted, then it probably means that `vmix` is disabled. In that case, OSS will use the rate requested by the program which uses the device, so this section does not apply. Exception to this are Envy24 (and Envy24HT) cards that have a special setting `envy24.rate` which has a similar function (see the `oss_envy24` manpage).

To change your sample rate:

1. First, make sure your card is able to use the new rate. Run `ossinfo -v2` and see if the wanted rate is in the Native sample rates output.
2. As root, run `/usr/lib/oss/scripts/killprocs.sh`. Be aware, this will close any program that currently has an open sound channel.
3. After all programs occupying `vmix` are terminated, run as root: `vmixctl rate /dev/dsp 96000` replacing the rate with your desired sample rate (and `ossmix envy24.rate 96000` if applicable).
4. Run `ossmix | grep rate` and check for `vmix0-rate <decimal value> (currently 96000) (Read-only)` to see if you were successful.
5. To make the changes permanent add the following to the `soundon.user` file:

    /usr/lib/oss/soundon.user

    #!/bin/sh

    vmixctl rate /dev/dsp 96000
    # ossmix envy24.rate 96000 # uncomment if you have an Envy24(HT) card

    exit 0

and make it executable.

### Disable virtual mixing and COOKEDMODE to reduce distortion

vmix is a virtual mixer audio that mixes multiple audio streams but can reduce the sound quality. Simply unchecking vmix-things in OSS Mixer GUI does not always work.

Turn off `COOKEDMODE` to disable format conversions for all applications and devices.

Edit the following:

    /usr/lib/oss/conf/osscore.conf

    cooked_enable=0
    vmix_disabled=1

Restart `oss.service` or your computer ifyou encounter errors.

After that you can still control the volume via ossmix or ossxmix.

### Start ossxmix docked to the system tray on startup

#### KDE

Create an application launcher file named `ossxmix.desktop` in you local application launchers directory (`~/.local/share/applications/` with:

    ~/.local/share/applications/ossxmix.desktop

    [Desktop Entry]
    Name=Open Sound System Mixer
    GenericName=Audio Mixer
    Exec=ossxmix -b
    Icon=audio-card
    Categories=Application;GTK;AudioVideo;Player;
    Terminal=false
    Type=Application
    Encoding=UTF-8

To have it autostart with your system, add it to the list in System Settings > System Administration > Startup and Shutdown > Autostart.

#### GNOME

As root create a file `/usr/local/bin/ossxmix_bg` with the following content:

    /usr/local/bin/ossxmix_bg

    #!/bin/sh

    exec /usr/bin/ossxmix -b

Then go to System > Preferences > Start Up Applications and:

- Click Add, type `OSSMIX` in the Name field and `/usr/local/bin/ossxmix_bg` in Command field then click Add Button.
- Login and logout to see the changes.

### Record sound output from a program

See upstream article on Recording sound output of a program.

### Suspend and hibernation

OSS does not automatically support suspend, it must be manually stopped prior to suspending or hibernating and restarted afterwards.

OSS provides `soundon` and `soundoff` to enable and disable OSS, although they only stop OSS if all processes that use sound are terminated first.

The following script is a rather basic method of automatically unloading OSS prior to suspending and reloading afterwards.

    /usr/lib/systemd/system-sleep/50osssound.sh

    #!/bin/sh
    suspend_osssound()
    {
        /usr/lib/oss/scripts/killprocs.sh
        /usr/bin/soundoff
    }

    resume_osssound()
    {
        /usr/bin/soundon
    }

    case $1 in
        pre)
            suspend_osssound
     	;;
        post)
     	resume_osssound
     	;;
        *) exit $NA
     	;;
    esac

Save the contents of this script (as root) into `/usr/lib/systemd/system-sleep/50osssound.sh` and make it executable.

Warning This script is rather basic and will terminate any application directly accessing OSS. Save your work prior to suspending/hibernating.

With this, all your applications should be fine.

### Changing the default sound output

When running `osstest`, the first test passes for the first channel, but not for the stereo or right channel, it sounds distorted/hisses. If this is what your sound is like, then it is set to the wrong output.

    *** Scanning sound adapter #-1 ***
    /dev/oss/oss_hdaudio0/pcm0 (audio engine 0): HD Audio play front
    - Performing audio playback test...
    <left> OK <right> OK <stereo> OK <measured srate 47991.00 Hz (-0.02%)>

The left sounded good, the right and stereo were the distorted ones.

Let the test continue until you get a working output:

    /dev/oss/oss_hdaudio0/spdout0 (audio engine 5): HD Audio play spdif-out
    - Performing audio playback test...
    <left> OK <right> OK <stereo> OK <measured srate 47991.00 Hz (-0.02%)>

If this passed the test on all left, right and stereo, proceed to next step.

For the command to change the default output see upstream's wiki article. Change it to what works for you, for example:

    # ln -sf /dev/oss/oss_hdaudio0/spdout0 /dev/dsp_multich

For surround sound (4.0-7.1) choose `dsp_multich`, for only 2 channels, `dsp` is sufficient. See this for all available devices.

### ALSA emulation

This article or section is being considered for removal.

Reason:

- It is weird to start with the old system and emulate the current one; probably what most people are looking for is how to run some old software that expects OSS on their system.
- This is not real emulation anyway. It is kinda trick for ALSA library configuration to use OSS drivers instead of ALSA ones. Might be useful 25 years ago, but definitely not now.
- Even libsalsa was dropped from AUR years ago.

(Discuss in Talk:Open Sound System#Emulation)

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 does not work with all applications. It does not 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`.

#### Instructions

- Install the alsa-plugins package.

- 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
    }

Note If you do not want to use OSS anymore, do not forget to revert changes in `/etc/asound.conf`.

### Settings for a specific driver

If something is not working, there is a possibility that some of your OSS settings are driver specific or just wrong for your driver.

To solve this:

- Find out which driver is used

    $ lspci -vnnd ::04xx

    00:1e.2 Multimedia audio controller [0401]: Intel Corporation 82801FB/FBM/FR/FW/FRW (ICH6 Family) AC'97 Audio Controller [8086:266e] (rev 03)
    Subsystem: Hewlett-Packard Company NX6110/NC6120 [103c:099c]
    Flags: bus master, medium devsel, latency 0, IRQ 21
    I/O ports at 2100 [size=256]
    I/O ports at 2200 [size=64]
    Memory at d0581000 (32-bit, non-prefetchable) [size=512]
    Memory at d0582000 (32-bit, non-prefetchable) [size=256]
    Capabilities: <access denied>
    Kernel driver in use: *oss_ich*
    Kernel modules: snd-intel8x0

- Locate configuration file for device in:

    # cd /usr/lib/oss/conf/

- Try changing defaults. There are only few settings, and they are self explanatory

For example, the setting:

    ich_jacksense = 1

in `oss_ich.conf` turns on `jack-sense` (which is responsible for recognizing plugged headphones and muting the speaker). Other settings for `jack-sense` can be found in `hdaudio.conf` where you have to change the `hdaudio_jacksense` variable.

- Restart the `oss.service` for changes take effects.

## Troubleshooting

### Troubleshooting HD Audio devices

#### Understanding the problem

If you have a HD Audio sound device, it is very likely that you will have to adjust some mixer settings before your sound works.

HD Audio 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 are also bad side effects, mainly because the HD Audio standard is more flexible than it perhaps should be, and because the vendors often only care to get their official drivers working.

When using HD Audio devices, you often find disorganized mixer controls, that do not work at all by default, and you are forced to try every mixer control combination possible, until it works.

#### Solution

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

You will probably want to setup a program to record/play continuously in the background (e.g. `ossrecord - | ossplay -` for recording or `osstest -lV` for playing), while changing mixer settings in `ossxmix` in the foreground.

- 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.
- Editing `/usr/lib/oss/conf/oss_hdaudio.conf`, uncommenting and changing `hdaudio_noskip=0` to a value from 0-7 can give you more jack options in `ossxmix`.

Note If you modify this file, restart the oss daemon for the changes to take effect.

### MMS sound cracking in Totem

If you hear various cracks or strange noises in Totem during playback, you can try using another backend such as FFmpeg. This will not fix the issue that somehow pops up in GStreamer when playing MMS streams but it will give you the option to play it with good sound quality. Playing it in MPlayer is simple:

    # mplayer mmsh://yourstreamurl

### Microphone playing through output channels

By default, OSS plays back the microphone through the speakers. To disable this in ossxmix find the "Misc" section and uncheck every "input-mix-mute" box.

### Add additional HD Audio sound cards support

The factual accuracy of this article or section is disputed.

Reason: Needs to be adapted to avoid referring to manual compilation : rebuilding ossAUR should be preferred, this section needs to link to the relevant page for customizing an AUR package. In particular, the last note is overly generic (dependencies should be handled by the PKGBUILD for example). (Discuss in Talk:Open Sound System)

OSS provides a "generic" codec driver that should be able to parse 99% of all HDAudio codecs.

If the device are not listed in the `oss_hdaudio.c` source file, add them to it, recompile and start the drivers.

To find the device/vendor IDs for "Multimedia controller" device class, do the following:

    $ lspci -nnd ::04xx

    00:1f.3 Audio device [0403]: Intel Corporation Sunrise Point-H HD Audio [8086:a170] (rev 31)

In this example, "Vendor ID" is "8086" and "Device ID" is "a170".

Change 5 lines of code in the source code, taking "the latest source package"(currently "oss-v4.2-build2020-src-gpl.tar.bz2") as an example:

    oss-v4.2-build2020-src-gpl/devlists/Linux

    oss_hdaudio     pci8086,a170    Intel High Definition Audio (PCH_C)

    oss-v4.2-build2020-src-gpl/kernel/drv/oss_hdaudio/.devices

    oss_hdaudio     pci8086,a170    Intel High Definition Audio (PCH_C)

    oss-v4.2-build2020-src-gpl/kernel/drv/oss_hdaudio/oss_hdaudio.c

    #define INTEL_DEVICE_PCH_C      0xa170
        case INTEL_DEVICE_PCH_C:		#Don't add it, it's already there

It is better to modify the existing "Controller" (`"PCH_C"` in this example), appending a new line of code may fail. It does not matter if it is `PCH_C`.

The last line of code is a bit complicated. This example is an ALC1150 sound card chip. The "Vendor_id" of "ALC1150" is "0x10ec0900", you can get it through a search engine, or try the following:

    # cat /sys/class/sound/card0/device/hdaudioC0D0/vendor_id

    0x10ec0900

    # cat /sys/class/sound/card0/device/sound/card0/hwC0D0/vendor_id

    0x10ec0900

For sound card chips of different manufacturers, different paragraphs need to be modified. In the example, the paragraph of Realtek manufacturer:

    oss-v4.2-build2020-src-gpl/kernel/drv/oss_hdaudio/hdaudio_codecids.h

      {0x10ec0889, "ALC889", VF_ALC88X_HACK, (char **) &alc883remap},
      {0x10ec0900, "ALC1150", VF_ALC88X_HACK, (char **) &alc883remap},
      {0x10ec0899, "ALC899", VF_ALC88X_HACK, (char **) &alc883remap},

It is very important that on the hardware of this example, modifying the second-to-last line works, but modifying the same code on the first-to-last line fails. You will need to try and modify the same code over and over on different lines to work on your hardware.

For example, try on the 4th last line:

     {0x10ec0887, "ALC887", VF_ALC88X_HACK, (char **) &alc883remap},
     {0x10ec0900, "ALC1150", VF_ALC88X_HACK, (char **) &alc883remap},
     {0x10ec0889, "ALC889", VF_ALC88X_HACK, (char **) &alc883remap},
     {0x10ec0892, "ALC892", VF_ALC88X_HACK, (char **) &alc883remap},
     {0x10ec0899, "ALC899", VF_ALC88X_HACK, (char **) &alc883remap},

Note

- Dependency packages required for compiling OSS do not need to be installed one by one, the base-devel meta package provides the tools for creating packages.
- You also need to install the toolkit for building kernel modules, which are built during the install phase.

## See also

- Official Website
- OSS Wiki
- OSS Forum
- Developer Information
- Git repository
- opensound-devel mailing list

Category:

- Sound

Hidden categories:

- Pages or sections flagged with Template:Out of date
- Pages or sections flagged with Template:Merge
- Sections flagged with Template:Remove
- Pages or sections flagged with Template:Accuracy

Open Sound System
Add topic