# Questions and answers

This section answers some frequently asked questions about &arts;.

General Questions

Does &kde; support my sound card for audio output?

&kde; uses &arts; to play sound, and &arts; uses the &Linux; kernel sound drivers, either OSS or ALSA (using OSS emulation). If your sound card is supported by either ALSA or OSS and properly configured (&ie; any other &Linux; application can output sound), it will work. There are however some problems with some specific hardware, please read the section for hardware specific problems if you're having problems with artsd on your machine.

Meanwhile also support for various other platforms has been added. Here is a complete list of how the most recent version of &arts; can play sound. If you have an unsupported platform, please consider porting &arts; to your platform.

&arts; audio I/O method | Comment
--- | ---
paud | Support for AIX Personal Audio Device
alsa | Linux ALSA-0.5 and ALSA-0.9 drivers
libaudioio | Support for generic LibAudioIO library which works on Solaris
nas | NAS sound server, useful for X Terminals with NAS support
null | Null audio device, discards sound silently
oss | OSS (Open Sound System) support (works on Linux, various BSDs and other platforms with OSS drivers installed)
toss | Threaded OSS support, which works better in some cases where the standard OSS support doesn't work well
sgi | SGI Direct Media support for IRIX
sun | Solaris support

I can't play `wav` files with &artsd;!

Check that &artsd; is linked to `libaudiofile` (``ldd` artsd`). If it isn't, download kdesupport, recompile everything, and it will work.

I hear sound when logged in as root but no other users have sound!

The permissions of the file `/dev/dsp` affect which users will have sound. To allow everyone to use it, do this:

- Log in as root.

- Open a &konqueror; window.

- Go into the `/dev` folder.

- Click on the file `dsp` with the right mouse button, and choose properties.

- Click on the Permissions tab.

- Check the Read and Write check boxes in all sections.

- Click on OK.

You can achieve the same effect in a terminal window using the command ``chmod` `666` /dev/dsp`.

For restricting access to sound to specific users, you can use group permissions. On some &Linux; distributions, for instance Debian/Potato, `/dev/dsp` is already owned by a group called audio, so all you need to do is add the users to this group.

This helps for &artsd;, but what about &kmix;, &kmid;, &kscd;,&etc;?

There are various other devices which provide functionality accessed by multimedia applications. You can treat them in the same way, either by making them accessible for everyone, or using groups to control access. Here is a list, which may still be incomplete (also if there are various devices in a form like `midi0`, `midi1`, ..., then only the 0-version is listed here):

- `/dev/admmidi0`

- `/dev/adsp0`

- `/dev/amidi0`

- `/dev/amixer0`

- `/dev/audio`

- `/dev/audio0`

- `/dev/cdrom`

- `/dev/dmfm0`

- `/dev/dmmidi0`

- `/dev/dsp`

- `/dev/dsp0`

- `/dev/midi0`

- `/dev/midi0`

- `/dev/midi00`

- `/dev/midi00`

- `/dev/mixer`

- `/dev/mixer0`

- `/dev/mpu401data`

- `/dev/mpu401stat`

- `/dev/music`

- `/dev/rmidi0`

- `/dev/rtc`

- `/dev/sequencer`

- `/dev/smpte0`

- `/dev/sndstat`

What can I do if artsd doesn't start or crashes while running?

First of all: try using the default settings in &kcontrol; (or if you are starting manually, don't give additional options besides maybe ``-F`10 `-S`4096` for latency). Especially full duplex is likely to break with various drivers, so try disabling it.

A good way to figure out why &artsd; doesn't start (or crashes while running) is to start it manually. Open a &konsole; window, and do:

    % artsd -F10 -S4096

You can also add the `-l0` option, which will print more information about what is happening, like this:

    % artsd -l0 -F10 -S4096

Doing so, you will probably get some useful information why it didn't start. Or, if it crashes when doing this-and-that, you can do this-and-that, and see how it crashes. If you want to report a bug, producing a backtrace with `gdb` and/or an `strace` may help finding the problem.

Can I relocate &artsd; (move compiled files to another folder)?

You can't relocate &arts; perfectly. The problem is that &artswrapper; has the location of &artsd; compiled in due to security reasons. You can however use the `.mcoprc` file (TraderPath/ExtensionPath entries) to at least make a relocated &artsd; find it's components. See the chapter about the `.mcoprc` file for details on how to do this.

Can I compile &arts; with gcc-3.0?

Short answer: no, &arts; will not work if you compile it with gcc-3.0.

Long answer: In the official release, there are two gcc-3.0 bugs which affect &arts;. The first, gcc-3.0 bug c++/2733 is relatively harmless (and has to do with problems with the asm statement). It breaks compilation of convert.cc. It has been fixed in the gcc-3.0 CVS, and will no longer be a problem with gcc-3.0.1 and higher. A workaround has also been added to the CVS version of KDE/aRts.

The second gcc-3.0 bug, c++/3145 (which is generation of wrong code for some cases of multiple virtual inheritance) is critical. Applications like &artsd; will simply crash on startup when compiled with gcc-3.0. Even if some progress has been made in the gcc-3.0 branch at time of this writing, still &artsd; crashes quite often, unpredictably.

What applications run under &arts;?

Obviously, all of the applications included with &kde; are &arts;-aware. This includes:

- &noatun;

- &arts-builder;

- &aktion;

- &kmid;

- &kmidi;

- &kmix;

- &kscd;

- &kde; games such as &kpoker; and &ktuberling;

Some &kde; applications that are not yet included in the &kde; release (⪚ in kdenonbeta) also support &arts;, including:

- &brahms;

- Kaboodle

- Kdao

The following non-&kde; applications are known to work with &arts;:

- xmms (with &arts; plug-in)

- Real Networks RealPlayer 8.0 (works with &artsdsp;; native &arts; support is being considered)

The following applications are known not to work with &arts;:

- none

See also the answers to the questions in the section on non-&arts; applications.

This section is incomplete -- if you have more information on supported and unsupported applications, please send them to the author so they can be included here.

Non-&arts; Applications

As soon as &kde; is running, no other application can access my sound device!

Since the &arts; sound server used by &kde; is running, it is using the sound device. If the server is idle for 60 seconds, it will auto-suspend and release it automatically.

You said it suspends after 60 seconds, it doesn't for me!

If you start artsd from the KDE control panel, the default is to suspend after 60 seconds. If you start artsd from the command line you need to use the -s option to specify the autosuspend time, otherwise it will default to disabling the autosuspend feature.

Currently it doesn't suspend when using full duplex. Turn full duplex off from the &kcontrol; and it will suspend. Disabling full duplex is generally a good idea anyway if you only use &arts; for playing audio and not recording.

How can I run old, non-&arts; applications?

Run them using the &artsdsp;. For instance, if you normally would run:

    % mpg123 foo.mp3

instead use:

    % artsdsp mpg123 foo.mp3

This will redirect the sound output to &arts;. This method doesn't require changes to the applications. It is something of an ugly hack however, and does not yet fully support all features of the sound card device, so some applications may not work.

I can't run &artsdsp; with any application, it always crashes!

You need a recent version of the glibc library; &artsdsp; will not work reliably on some older &Linux; distributions. For instance, on Debian 2.1 (which is glibc 2.0 based) it doesn't work, while on Debian 2.2 (which is glibc 2.1.3 based), it does.

Are there theoretical limitations with some applications that will prevent them from ever working with &artsdsp;?

No. Using &artsdsp; can result in slightly more latency and CPU usage that using the &arts; APIs directly. Other than that, any application that doesn't work should be considered a bug in &artsdsp;. The technique used by &artsdsp; should, if implemented properly, allow every application to work with it (including large applications like Quake 3).

What can I do if an application doesn't work with &artsdsp;?

You can wait for &artsd; to suspend or use the command ``artsshell` `suspend`` to ask the server to suspend itself. You will only be able to suspend the server if no &arts; applications are currently using it, and no &arts; applications will be able to run when the server is suspended.

If the server is busy, a crude but effective way to get rid of it is:

    % killall artsd ; killall artswrapper
    Now start your own application.
    % kcminit arts

Any currently running &arts; applications may crash, however, once you kill the server.

What about applications written for &kde; 1.x?

If you are running &kde; 1.x applications, which output sound via the &kde; 1 audio server, you will need to run kaudioserver to make it work. You can start kaudioserver in the same way than other non-&arts;-applications:

    % artsdsp kaudioserver

You will need to have installed kaudioserver (from the same source where you got your &kde; 1.x applications from) - it belongs to &kde; 1.x, not &kde; 2.

What about applications using the enlightened sound daemon, ESD?

The issue is similar than with kaudioserver. Such applications will need a running esd server. You can start `esd` via &artsdsp;, and every ESD aware application should work fine, like this:

    % artsdsp esd

Newer versions of aRts (>= 1.2.0) also can also use the enlightened sound daemon instead of directly accessing the soundcard. On the command line, you can use the -a option, such as

    % artsd -a esd

to get EsounD support, whereas in KDE, you can use kcontrol to configure artsd to use esd via Sound -> Sound Server -> Sound I/O.

Latency

I sometimes hear short pauses when listening to music, is this a bug?

This is most likely not a bug, but caused by the fact that the &Linux; kernel is not very good at real-time scheduling. There are situations where &arts; will not be able to keep up with playback. You can, however, enable real-time rights (via &kcontrol;), and use a large latency setting (like 250ms or don't care), which should improve the situation.

What's the effect of the response time setting?

The help text for this setting in the &kcontrol; can be misleading. A lower value means that &arts; will take less time to respond to external events (&ie;. the time that it takes between closing a window and hearing a sound played by &artsd;). It will also use more CPU resources, and be more likely to cause dropouts.

Is there anything else I can do to prevent pauses?

For users of IDE drives, you can use the `hdparm` command to put your IDE drive in DMA mode. A word of warning: this does not work on all hardware, and can result in having to do a hard reset or in rare cases, data loss. Read the documentation for the `hdparm` command for more details. I have successfully used the following command:

    % hdparm -c1 -d1 -k1 -K1 /dev/hda

You need to run this after every boot, so you might want to place it in a system startup script (how to do this distribution specific, on Debian &Linux; it is usually put in `/etc/rc.boot`).

Realtime priority doesn't seem to have any effect for me?

Verify that artswrapper is really installed suid root, like it is supposed to be. A lot of distributions (SuSE7.x for instance) don't do this. You can verify this using: ls -l $(which artswrapper). Good:

    % ls -l $(which artswrapper)
    -rwsr-xr-x    1 root     root         4556 Sep 24 18:05 /opt/kde2/bin/artswrapper

Bad:

    % ls -l $(which artswrapper)
    -rwxr-xr-x    1 root     root         4556 Sep 24 18:05 /opt/kde2/bin/artswrapper

If you are not having the s, you can get it using:

    % chown root $(which artswrapper)
    % chmod 4755 $(which artswrapper)

If you make &artswrapper; SUID root, it will likely improve the quality of your audio playback by reducing gaps in the music. However, it also increases the risk that a bug in the code or a malicious user can crash or otherwise harm your machine. In addition, on multi-user machines, prioritizing high-quality audio may result in deteriorated performance for the users who are trying to make productive use of the machine.

Why is &artsd; taking so much CPU time?

Check your response time settings. However, the current version is not yet really optimized. This will improve, and until then no real prediction can be made how fast &artsd; can or can't be.

Network Transparency

What do I need for network transparency?

Enable it in the &kcontrol; Sound Server settings (enable X11 server for security information and network transparency). Then copy your `.mcoprc` to all machines you plan to use network transparency from. Log in again. Make sure that the hosts that interact know each other by name (&ie; they have resolvable names or are in `/etc/hosts`).

This should be all you need to do. However, if it still doesn't work here are some additional details. The &arts; sound server process, &artsd;, should only run on one host, the one with the sound card where the sound should be played. It can be started automatically on login by &kde; (if you configure that in &kcontrol;), or manually using something like:

    % artsd -n -F 5 -S 8192

The `-n` parameter is for network transparency, while the others configure latency.

Your `.mcoprc` file should have this entry:

    GlobalComm=Arts::X11GlobalComm

on all machines involved, in order for network transparency to work, This is what is enabled by the X11 server for security information control panel setting.

Finally, in any &kde; version in the 2.0.x series, there is a bug which applies if you don't have a domain name set. Clients of &artsd; try to find where to connect to via the hostname.domainname combination. If your domain name is empty, it will try to connect to hostname. (note the extra dot). Adding an entry like this to `/etc/hosts` (&ie; `orion.` if your hostname is orion) works around the problem.

How do I debug network transparency if it doesn't work?

Assuming you have the &kde; source code, go to `kdelibs/arts/examples`, and run ``make` `check`` to compile some programs, including referenceinfo. Then run

    % ./referenceinfo global:Arts_SimpleSoundServer

The output will indicate the host name and port being used by &arts;. For example, `tcp:orion:1698` would mean that any client trying to use network transparency should know how to reach host orion.

Hardware specific questions

What hardware artsd doesn't work well with?

It seems that there are a few linux drivers which don't work well with aRts in some kernel versions. Please read this list before reporting a bug. If you find that some information in this list is incomplete, please don't hesitate to let us know.

Linux Driver / Soundcard | Fails under | Works under | Remarks
--- | --- | --- | ---
i810 driver (Intel 810 + AC97 Audio) | 2.4.9 | 2.4.18, 2.2.20, commercial oss driver, alsa-0.5.12a with OSS emulation | driver causes cpu overload (see below)
maestro 3/4 chipset | 2.4.9 | ? | driver sometimes causes cpu overload (see below)
aureal8820, aureal8830 drivers from sourceforge | 2.4.17 | ? | driver triggers assertion / causes cpu overload (see below)
OSS Commercial 3.9.4g with Aureal Vortex | ? | ? | system lockup
ymfpci | 2.4.0, 2.4.12 | 2.4.17 | driver triggers assertion (see below)

Why are there hardware specific problems and how do I see them?

The usual problem is that the driver doesn't supply aRts with enough or accurate enough information on when to write sound data. Most OSS drivers do supply correct information, but not all.

You might notice that some other applications (like xmms) may not need this data, and thus work correctly even with your hardware. However, &arts; needs this data, so artsd might fail. This is still a bug in the driver, and not in &arts;.

There are two kinds of behavior that artsd exposes on being run on an incorrect driver. Either, it continously tries to feed new data, but never really succeeds, which eventually leads to consuming all CPU power and reporting cpu overload and exiting. The other problem is that artsd might get supplied with wrong information how much to write. Artsd will then stop with an assertion like:

    artsd: audiosubsys.cc:458: void Arts::AudioSubSystem::handleIO(int):
    Assertion `len == can_write' failed.
    Aborted

What is wrong in the driver if I get the cpu overload problem?

Usually, artsd uses select() to find out when to write new data. Then, it uses an ioctl(...GETOSPACE...) to find out how much data to write. Finally, it writes this data.

A problem occurs if artsd is woken up either always or if there are minimal amounts of data to write. The OSS documentation specifies that select() only wakes up a process if there is at least one fragment to write. However, if artsd is woken up if there isn't data to write, or very little, for instance one sample, then it will keep writing little pieces of audio data, which can be very costly, and eventually overload the cpu.

To fix this, the driver should wake up artsd only if there is a full fragment to write.

What is wrong in the driver if I get the assertion?

Usually, artsd uses select() to find out when to write new data. Then, it uses an ioctl(...GETOSPACE...) to find out how much data to write. Finally, it writes this data.

If artsd can't write as much data as indicated by the ioctl, it will fail in the assertion. To fix this, the driver should supply the correct amount of free space.

Other Issues

I can't use &arts-builder;. It crashes when executing a module!

The most likely cause is that you are using old structures or modules which aren't supported with the &kde; 2 version. Unfortunately the documentation which is on the web refers to &arts;-0.3.4.1 which is quite outdated. The most often reported crash is: that performing an execute structure in &arts-builder; results in the error message [artsd] Synth_PLAY: audio subsystem is already used.

You should use a Synth_AMAN_PLAY instead of a Synth_PLAY module and the problem will go away. Also see the &arts-builder; help file (hit F1 in &arts-builder;).

Recent versions of &arts-builder; (&kde; 2.1 beta 1 and later) come with a set of examples which you can use.