Note that I do not work for Skype nor have any affiliation with them - I just thought I'd chuck together a few solutions to common sound problems in Linux, seeing as I've dealt with a few of them. If you have something to add, please do! Should probably add a section on configuring OSS... I'm doing this in the hopes that it will help new Skype/Linux users, and that we might avoid some repeat questions on the forums. Anyway, here goes.

Unofficial Skype + Linux Sound FAQ

Q: I have no sound in Linux at all!

In order for Linux to recognize and use your soundcard, you have to load the appropriate driver. As of the 2.6 version of the kernel, that means enabling the ALSA (Advanced Linux Sound Architecture) driver for you card. Take a look at the ALSA Soundcard Matrix to determine which driver you are supposed to use for your speciffic card.

Now, you will have to modify your /etc/modules.conf or /etc/modules.d/alsa (check your distribution for details on the correct way to load and configure modules) and add the following:


Note that a lot of this configuration is dedicated to something called OSS (Open Sound System) emulation. This mimics the behaviour of the old Linux sound system so as to be backward compatible with older software that does not yet support the new sound system. One such piece of software is Skype - so it is important that it is running and configured correctly.

Now, it is time to load the drivers. How you do that depends on your distribution - you may have an /etc/init.d/alsa or similar script that will do it for you. If you are unable to figure it out, a reboot will do it.

For a great and detailed walkthrough on setting up ALSA and setting the ALSA mixer correctly, please read roothoricks excellent post on the subject here.

Q: My driver loaded correctly but I still have no sound!

The first thing you should do is run the "alsamixer" program. By default, all channels are muted on a newly installed ALSA system so you will have to manually unmute the ones you want. The best tool for the job is alsamixer, which can access all the different channels offered by ALSA.

It might also be a permission problem. Initially, though that might depend on your distribution, I believe the sound devices are owned by root and only root has read/write permissions on it. If you system has an "audio" group in /etc/group, try adding yourself to that one. As root, execute the following command:

Replace username with the name of the user you're going to run Skype with. You can also change the ownership of the dsp device so you can access it as a regular user, or set the permissions so that all users have read/write access to the device.


The first line will make username the owner of the device. The second line will give everyone with an account on the system read/write access to the sound device. Note: You might have a /dev/dsp device even if you are using devfs - this will just be a symlink to /dev/sound/dsp so you do not have to fiddle with it.


Q: OK, now I can hear sound, but noone can hear me speak!

Read the section above again - and make sure you have both read ® and write (w) permissions to the dsp device. To learn more about UNIX file system permissions, take a look at the chmod man page.


Also verify that your sound driver supports "full duplex" - that is, if it can both play and record sound at the same time. A lot of OSS drivers do not support that, however most ALSA drivers do. Also, see below on how to configure KDE's sound system to use full duplex.

Q: Weee! Now I can listen to music and record my voice! But I still can't hear anything in Skype?

Are you using a desktop environment such as KDE or Gnome? Those both have "sound daemons" that take over control of the soundcard once it starts, and unless an application knows how to communicate with those sound systems they will not be able to use the sound device. Unfortunately, Skype will try to access /dev/dsp directly, instead of querying any running sound daemons. However, both Gnome and KDE have means to "redirect" such requests to the respective sound systems by launching uncooperative applications through a special wrapper - artsdsp for KDE and esddsp for Gnome.


In order for artsdsp to work correctly with Skype, you need to make sure that Full Duplex mode (see above) is enabled. Open up your controlcenter, select "Sound & Multimedia"->"Sound System". On the "Hardware" tab, check the box next to "Full duplex".



Please note that this checkbox will be enabled wether or not your soundcard actually supports full duplex operation. Enabling full duplex in the KDE sound system with some OSS drivers that do not support it, will make artsd crash horribly and possibly hang your computer. Needless to say, you might not want to do that,

Q: I have a USB headset - why doesn't Skype use it?

Please make sure you are running the latest version of Skype. Version 0.91.0.12 and up support using alternate DSP devices for sound IO, selectable from the "Hand/Headsets" tab in the Options dialog. Your primary soundcard will most likely be /dev/dsp, and any additional sound devices such as USB headsets will be /dev/dsp1, /dev/dsp2 and so on. If you have multiple USB devices (such as webcam mics) you may have more than one additional sound device. Please note that currently you cannot use separate devices for input and output, so make sure the device you are using supports both.

Q: Skype works now - but why is there a horrible echo?

This could be caused by a few things. First of all, using a microphone and loudspeakers is not a good idea, and might cause echo. You may still experience echo even if you are both using headsets. This is usually caused by something called the "Capture" channel - a channel present in some soundcards, and often enabled by default. Start up your mixer application, and verify that the "Capture" channel is muted. Good (input) mixer settings for Skype should look something like this:



An unmuted "Capture" channel can also cause bad sound quality and other artifacts, so always leave this muted.

Q: I have Skype working with artsd/KDE - but there is several seconds of latency/delay

There are two things you can do to reduce this delay. Open up your "sound system" config in Controlcenter and check two things:

o Is artsd running with realtime priority? If not, check the appropriate box. If you get an error message, you may need to set the SUID bit on artswrapper (make it run as root when launched). To do this, execute:


o Check your buffer settings ("Skip prevention"). A large sound buffer will cause more latency. Decreasing the buffer size may cause sound to skip when CPU loads go up, but running artsd with realtime priority should drastically reduce the chances of this.

Q: Additional notes about kernel and drivers

If you are having issues with your sound drivers or OSS emulation not working properly, there are a few things you can check. First of all, avoid the native 2.4 kernel OSS drivers if you can, especially for newer or less common sound cards. These drivers are all but obsolete and poorly maintained, and a lot of them do not support full duplex operation or even sound recording.

If you experience a lot of sound issues after building your kernel and drivers, it could be a good idea to disable support for ACPI (Advanced Configuration and Power Interface) when you are testing. ACPI support on some motherboard/BIOS setups is horribly broken, and the kernel ACPI drivers cannot work around this. The drivers are in themselves a bit experimental, which does not help the issue at all.

Common problems with ACPI is hardware not being detected properly, hardware performing erratically or even hanging the computer etc. I have personally worked with machines that would even crash and hang indefinitely during boot when ACPI was enabled. Disabling ACPI can be done at kernel compile time by disabling it, or at boot time by appending "acpi=off" on the boot prompt (LILO) or by editing the boot parameters (Grub). Disabling ACPI will have no adverse effects on a desktop computer, but you will not be able to monitor the onboard fan/temp sensors if you disable ACPI. On a laptop computer you might be a bit worse off though, since you will have no power management facilities.

That was helpful. Esp. the info about artsdsp and capture. Capture must be the most annoying feature in the universe. It results in horrible echo. The Kmix program can do a lot of things but all of them are confusing.

I am still working with Kmix to figure out how to turn off capture. It seems that the soundcard wants to play mic input back into my headset, no matter what I do. There must be a way to stop this, right? It seems bizzar to have a soundcard that always plays its mic input to the speaker; that seems like a "feature" which is never really desirable, right? But is there a way to stop it?

That's not necessarily the capture channel; as long as your microphone input is enabled and not muted you will hear your own voice when speaking into the microphone. This will not cause any echo or other audio distortions though, as long as the capture channel is not enabled and is muted you're set.

This is completely mysterious. I can't hear who I'm talking to, but I get tremendous echo. Is this maybe a problem on the far end? I attempted to attach snapshots of the Kmix windows, but it's not letting me upload any files so I can't include an image.

Yeah, if you get your own voice back, I'd say the problem is at the other end. I can host your image for you if you like, just send me a PM and I'll sort it.

One warning about artsdsp... It does not always
work as you indicated, quite often you lose mic settings and mic control all together.

For this to work you have to have arts running in full duplex mode, but some sound cards don't support that and system lockups can occur.

Arts "gets out of the way" of alsa and oss if you have autosuspend selected, but most probably that means no sound at all while skype is loaded even when not in a call, UNLESS you pipe thru artsdap. So fiddeling around getting this to work is worth while.

Newer arts may not have this problem with all
sound cards, but kde 3.1.x usually will have artsdsp problems with some things like teamspeak and skype.

Hm, using KDE 3.2.3 (artsd v. 123) I have noticed no such problems. But you bring up a vaild (FAQ-worthy ) point - Full Duplex. Yes, that can be a problem if you are using the old OSS drivers (not ALSA+OSS emu). A lot of OSS drivers do not support full duplex and will crash artsd horribly if you try to enable it. Most ALSA drivers do support full duplex though.

Well keep on inserting these things into the main faq as people bring them up, because this page is way more usefull than most of the official pages. Its a good Faq. Good-On-Ya.

FAQ ammended - I'll keep updating as new stuff pops up =)

Futt and others, thanks for this. It's useful and I'm changing the posting type to sticky so it stays on top of the thread list (but you can still add/change postings).

Thanks a lot Terminus! I'll do my best to keep it up to date.

hallo, hallo, great FAQ, v. helpful stuff about artsdsp and using alsa (which i only recently managed to get to work and maybe _just_ maybe i will be lucky enough to get my PDT cyberphone (not cyberphoneK) headset to work soon enough.

wanted to mention: you referred to and say "see below" on how to set Full Duplex in KDE but did i miss the question and its answer?

l.

In the question below the one you refer to:


But yes, it is maybe a bit messy. I'll see if I can figure out how to make anchors with bbcode and do some reformatting.

Arrrgh!
Thanks for the excellent FAQ.
If only artsdsp could deliver decent latency. Right now when I use it it's like talking to someone on Mars.

So I have two possible setups
1) can hear the phone ring, but cannot have meaningful conversation (seven second + delays) when client runs under artsd
2) cannot hear the phone ring (because artsd is running) but once i stop using artsd it turns itself off automatically and I can have sub 500ms conversations.

It's a pain.
The client needs either popup notifications or some sort of sound infrastructure support desperately.

At the moment people are IMing me in MSN to let me know they're phoning. How dumb is that?

There are a few ways to reduce the latency a bit. Open up your "sound system" config in Controlcenter and check two things:

o Is artsd running with realtime priority? If not, check the appropriate box. If you get an error message, you may need to set the SUID bit on artswrapper (make it run as root when launched). To do this, execute:


o Check your buffer settings ("Skip prevention"). A large sound buffer will cause more latency. Decreasing the buffer size may cause sound to skip when CPU loads go up, but running artsd with realtime priority should drastically reduce the chances of this.

Hope that helps (will be adding it to the FAQ anyway )

I couldn't get it to work with esddsp. It wouldn't play nor record any sound using the gnome sound daemon.

I've tried the libesd0 and the libesd-alsa0 versions. My kernel is 2.6.6 with ALSA + ALSA's OSS Emultated, configured simillarly to the way described in the FAQ. My sound card is an onboard CMI8738-MC6 (snd-cmipci module).

Without the wrapper, using the plain OSS emulated on ALSA it works great. But most of the time i'm listening to music/other sounds, so I just can't get skype to work.

Any hints ? I don't know what could be going wrong, Skype outputs only events related to the UI.

many thanks in advance for any help

Xba

Ah, as you may have noticed from the slight KDE bias in the FAQ, I don't use gnome much at all. I'll have a look at esd once I get back to my own PC (stuck on windows on a friends PC at the moment).

EDIT: added a link to roothoricks excellent post on ALSA configuration

I got skype working fine and everyone can here me but every time i try to do something else on my computer that uses sound it doesn't play while i'm in a call... for instance when I try to play music in XMMS while I am already in a call XMMS freezes and won't let me do anything in the program until I exit. It seems that skype is taking over?!?! How do I change this?

I believe it is because Skype uses OSS (or ALSA OSS emulation). The default behaviour for OSS is that the sound device be opened in "blocking" mode - that is the application gets exclusive access to the device. With ALSA, you can try to force applications to open it in non-blocking mode by appending this line to your modules.conf:

I have not been able to get this to work realiably though, and would recommend using artsdsp/esdsp if you are using gnome or KDE. Availability of this feature also depends on your soundcard/driver.

Thanks again for futt and all the others for help in compiling and maintaining this info. From my side as a KDE user, a setting that helped me was the "Sound buffer" in KDE sound system settings. It was already with "realtime priority", but when running with too large buffer, it started cutting. Now I have the buffer set to 46 milliseconds (4 fragments with 2048 bytes) and it works with artsdsp like a charm. Tip: for playing MP3-s at the same time with xmms, use its "xmms-arts" plugin for sound output which outputs sounds through arts

My patch against skype_dsp_hijacker, which enables me (and hopefully others, too!) to use separate devices for sound input and output can be downloaded from

http://195.38.3.142:6502/skype/

With this, my USB webcam microphone works as an input device, while still getting sound output sent to the soundcard.

It may or may not work on your system.

Please tell me if you find this useful!

The original skype_dsp_hijacker can be found at
http://suedpol.dyndns.org/skype/

Regards
Jan Albin
jan@nsgroup.net

I was intereste to see the posts about turning off capture and using mic. I have the reverse experience: on my Centrino laptop with Intel I82801 sound chip, in order to get my microphone to work I have to switch capture on.

Further, if I have mic switched on, then the microphone feeds back into the sound system.

This seems to be pretty much the reverse of what others have experienced here, so I thought it worth mentioning; perhaps a note could be added to the FAQ saying that if the recommended action of muting capture and turning up mic doesn't work you may want to do the reverse.

Yes that is odd - everyone else I have talked to have the exact opposite experience, hm. One thing worth noting though, is that you can safely mute the microphone (if you are using KMix, that means switching off the little green light on top of the mic control). That would eliminate the "feedback" effect you mention. If the microphone is not muted, you will be able to hear yourself when you talk into the mic. In my screenshot in the FAQ it is actually shown as unmuted, but that is not a requirement for the mic to work in Skype.

Hi all!

Little problem:

Skype 0.90.0.14, ALSA 1.0.2, AUDIGY driver.
I can hear sound, but noone can hear me speak

Skype 0.90.0.14, ALSA 1.0.2, emu10k1 driver.
All OK.

What is the ...?

Some audigy cards can be a bit of a headache to configure correctly - especially some of the versions that come integrated on motherboards - been a lot of discussion about that on misc. mailing lists.

Have a look at this audigy FAQ and see if any of the hints there help you. Also, fire up the alsamixer and check that you have everything set correctly (by default, all channels are muted).

Thanks for the link, but it has not helped. I have Mandrake 10.0 with kernel-2.6.3. Audigy card is not integrated to MBoard.

When I toggle to audigy driver - my speak is not heared for opponent, but I hear my voice in headphones! If I toggle to emu10k1 driver - all work correctly.

Full duplex is on, mixer settings is right (no muted ).

OK, do you use any desktop environments (KDE, Gnome etc)? How do you launch Skype, do you use esddsp/artsdsp?

I'm using KDE. And artsdsp, of course

Permission to /dev/dsp is right (read/write for user ilya)

Skype installed from rpm, launch from desktop, click to icon.

P.S. OK, I'm trying to lounch skype from console.

OK, are you using MMAP mode (the -m parameter to artsdsp)? What about duplex settings in the control center - is it enabled?

I'm using the "Suond system settings" in KDE settings, and don't now, what parameter in artsdsp.

Full duplex is enabled.

Now I starting system with audigy driver and if you can, you may call to me. I'm online.

my "number" is ilya_shpankov

Okay, I have this same problem. I can hear the phone ringing, I can hear others speak. But they don't hear me. I haven't tried the 'artsdsp -m' solution yet; there aren't so many people willing to be test subjects. Will this make a difference? Will try when I have the chance. All suggestions and solutions checked and correct (full duplex, etc.).

I run KDE 3.2 and Linux 2.6.3-- I guess that means ALSA, but I have no OSS API emulation, I think. Is this necessary? Why?

Thanks!

This is strange. I've never had any problems with sound, but apparantly ALSA knows no soundcards!?



EDIT: I found out I have both old OSS and ALSA compiled in my 2.6.3! Why do these not conflict? Apparantly, deprecated OSS takes precedent over ALSA??

Enabling both OSS and ALSA is a bad idea; what you want to do is disable OSS and load the ALSA modules. OSS emulation is also required for Skype to work with the ALSA drivers.

So in short; get rid of the old OSS drivers, install the ALSA drivers and OSS emulation. Should work a lot better.

Oh and if any of you want to test it out, feel free to call if I'm online (usually am during day/evening/night CET).

So, it's my test:

I think, all OK. Or not?

Yeah, so I disabled OSS and now only have ALSA with OSS emulation (as module) in kernel... sound is not working at all now, but I have no time to go further into this now.

Have a look into /proc/asound/oss/devices and see if the OSS emulation is setup correctly. The ALSA driver looks like it is correctly configured though.

Hey, man. Thanks for your help so far. It's still not working right; right now I have sound working but it sounds way messed up. Cracking, noise, especially when I increase the IGain. Then it's just horrible. It's all distorted. I've upgraded to 2.6.7, no difference. I think I read about this somewhere. Here's some more info:



I have a SoundBlaster 128 PCI here. I *think* it's the right driver... The ENS1370 didn't give me sound at ALL.

*sigh* I'm gonna look further into this now. Maybe I'll just go back to OSS. At least that WORKED.

Distorted sound is in my experience mostly the fault of an unmuted "Capture" channel. If this channel is not muted, you will get feedback loops, echo, distortions and all manners of nastyness.

Check the KMix screenshot in the FAQ, you should be able to locate the channel and mute it.

Yeah, that screenshot had me wondering... I don't have half the options in that screenshot. I use KMix 2.0.1 in KDE 3.2.3. This is how my KMix looks:




There are not many options within KMix for me...

EDIT: Also, the Digital1 channel can only be either 0 or 1. No values in between. Weird.

Okay, I got ALSA on Debian working, finally. Running 2.6.7 kernel with Debian patches now. ALSA wasn't working until I apt-get install'ed the alsa-base package. Apparantly this is required.

Then I still got horrible noise. Turns out I got to disable IEC958 from KMix's Advanced controls. No idea what it is. But now I have lots more options in KMix.

Still haven't had a chance to try out Skype, though. Need test subjects.

Heh!

All OK!

I'm reinstall Mandrake, and after this starting the alsaconf-script. In modprobe.conf have appeared all needed drivers and Skype is work correctly.

Thanks to all!

Exclusive thanks to futt!

Glad you got it working =) Some weird problems there, all related to ALSA setup. It's a bit of a hog to configure using modules on some systems apparently - might as well build it into the kernel to save some headaches =)

Good luck guys.

No, it's undesirable. Then, for example, it should to recompile a kernel with each release of new drivers ALSA.

Hi folks,

just my 2 cents: I noticed that the issue with the choppy sound under Linux can depend on the hardware you are using.
I use it on two machines with different hardware but the same software and settings.

One is Athlon XP 2000+, 1 GB RAM, nforce2 chipset with intel8x0 sound driver for Alsa 1.0.5. Sound buffer under KDE s 92ms. This works perfect for me and the sound is superb, also for Skype-Out. And I used it to call my friends on the other side of the globe (Asia -> Europe).

On the other machine (laptop: Acer Travelmate 351, Intel 700 Mhz CPU, 256 MB RAM, Ali-5451 chip on-board) the sound is still choppy, but I think I found the optimum settings with the sound buffer (also 92ms).

Software is Debian sid on both machines.

So, don't blame Skype, get better hardware!

Cheers

Hehe true, true - although your tavelmate seems to be within the minimum spec stated for Skype, this beta version will be more resource hungry due to the way it is compiled. I don't know for sure of course, but normal procedure when building an application for debugging purposes is to disable all optimization settings and enable a lot of resource-hungry debugging options. This will of course raise the minimum specs significantly.

In the mean time, you can compensate for some of it by tweaking your kernel a bit (2.6 kernel with optimizations such as preemptive scheduling and low-latency for instance) and play around with process priorities (nice) and your sound daemon (artsd/esd) buffer- and priority settings.

Hi folks,

I have had some trouble installing skype on a gentoo dist with kernel 2.4 and without alsa. I need help! Skype installs w/o any problem however I am not able to hear nor transmit any sound.

I am not using kde nor gnome jsut fluxbox.

thanks
gargola

I'm running gentoo with the 2.4 gentoo-sources here. I use ALSA instead of the default OSS drivers though, since full duplex is not supported by the OSS driver for my soundcard - it could be that you have the same problem? Will need to know more about your setup first though - what soundcard, which driver etc. Have you got sound/recording capabilities in other applications? Try teamspeak for instance - if that works, so should Skype.

Hi,

I have tried all of the suggetsions in the first post of this thread but I am still unable to get sound working in Skype (QT static build).

I have:
used esddsp to run skype: no luck
killed the esd daemon: no luck
changed permission on /dev/dsp: no luck
fiddled with muting and locking in the mixer: no luck
(NB there is no capture channel listed in the mixer)

Running Ximian Desktop 2 on RedHat 9.0 (2.4.20 kernel). Hardware is intel onboard sound (i815). Sound works perfectly in Sound Recorder and other linux programs, but nothing in or out of Skype.

Any suggestions?