How to fix Skype audio problems in Ubuntu 13.10 on a ThinkPad T61?

Symptoms

This issue started to occur right after installing Ubuntu 13.10 on a ThinkPad T61 with an "Intel Corporation 82801H (ICH8 Family) HD Audio Controller (rev 03)" according to lspci. So, whenever I do one of these:

• adjust volume with the hardware volume silence / up / down buttons, only while not in a Skype call
• adjust volume with an equivalent software mixer feature, only while not in a Skype call

the effect is this:

• the next Skype call will be completely silent (both output and input do not work)
• the Skype call after that will play a randomized variant of rattling noise for output, while input probably works fine (judged by the level bar indicator); interestingly, the closing sound of the Skype call will play correctly, which indicates that only one of the audiostreams is not initialized correctly (the Gnome sound settings panel shows that two are in use during a call)
• the Skype call after that will play also the output, but with lots of stuttering in between
• the Skype call after that will play the output correctly, and the input will also work fine

For this to be repeatable, allow for some 3-5 seconds of separation between calls. At times, these four steps will also be reduced to three, or the "rattling noise" or "stuttering" step could also occur two or more times.

In addition, there is a similar problem with Skype chats. Whenever I do one of these:

• send a message

the effect is this:

• a randomized variant of permanent, rattling noise (the "message sent" sound will not be sent)

This noise will persist also through Skype calls initiated afterwards. It will (in most cases) change when sending another message, and after some messages will also completely disappear again. The surefire way to make it disappear is though when your chat partner sends you a message.

Solution

The reason for this behavior is that Ubuntu 13.10 ships with PulseAudio 4.0, and Skype does not properly support that so far [source].

The proper solution is to simply install Skype from the Canonical Partner repositories (so, not by manually downloading a Skype .deb via its website). It contains a patch to the skype.desktop file that starts Skype now with a proper workaround as "env PULSE_LATENCY_MSEC=60 skype" [source].

However, if like me you're used to start applications via the Alt+F2 mini-terminal, you might even have this patched Skype package installed, and it has still no effect to fix your audio in Skype. As you probably want to keep starting Skype by hitting Alt+F2 and typing skype, here is a way to do so:

1. Createa file /usr/local/bin/skype, with the following content:

   #!/bin/bash

   # Workaround for the Skype incompatibility with PulseAudio 4.0, as explained in
   # http://www.webupd8.org/2013/10/get-sound-working-in-skype-with-ubuntu.html
   #
   # This is already installed in the Ubuntu Saucy Skype package from Canonical Partner repos, however their
   # solution of prepending an environment variable in the .desktop file is not used when starting Skype
   # via the Alt+F2 mini-terminal. To apply the solution for that too, we need this file to supersede the normal
   # Skype command. Use "which skype" to confirm that the skype command afterwards indeed refers to
   # /usr/local/bin/skype instead of /usr/bin/skype.

   env PULSE_LATENCY_MSEC=60 /usr/bin/skype

2. Give proper execution rights to that file.
3. Check with which skype to make sure Skype is now called from /usr/local/bin/skype instead of from /usr/bin/skype.

There are also some dirty workarounds (here mentioned only to learn something about Skype and Pulseaudio, not to use them):

1. Do not use volume buttons except when in a Skype call. This is not practical of course.
2. Disable Skype sound events for "Call Connecting" and "Chat Message Sent", and maybe all others. This can be done in the Skype "Options -> Notifications" menu item. This however can result in Skype calls falling completely silent, and this will also not fix itself in the next call then. (It can however be fixed, right during the call even, by playing some seconds of sound from a different application.)
3. Create the permanent random noise, then mute it via the "System Sounds" stream. This works as follows:
   1. Disable the "System Sounds" PulseAudio stream by going to the Gnome Sound Settings dialog, there to tab "Sound Effects" and set "Alert Volume: Off". Alternatively, in Skype go to "Options -> Sound Devices -> Open Pulse Audio Volume Control -> Playback", and click the "Mute audio" button for stream "System sounds".  In both cases, you will notice that the Skype sound channel in the "Applications" tab (if there is one, usually only after step 2) also goes silent, and with it the Skype notifications in chats, and your volume level adjustment feedback sound goes silent as well (explanation see below).
   2. Let Skype create a sound mess. You have to create that permanent random noise, either by using the "send chat message" technique from above (with a notifocation sound enabled of course), or by test playing any notification sound via Skype's "Options -> Notifications -> Test Event" button. (You can not use the random noise generated by a Skype call with broken audio from above.)
   3. Now do whatever you want in Skype, the problem with corrupted sound in calls will not appear any more, even when using volume adjustments in between of calls.
   4. You have to repeat step 2 after a restart of Skype. (The muting of the System Sounds stream stays active after Skype quits because it is not a Skype feature; however Skype is only immune against creating corrupt audio in calls once it has corrupted the System Sounds audio by executing step 2.)

Explanation Attempt

Let me try a little explanation (just from observations, I do not know how PulseAudio works internally): The problem of Skype seems to be that it cannot properly write to the "System Sounds" stream if another application has written to it in between (including the feedback sounds of the volume change buttons). When Skype tries to write to the System Sounds stream in this situation, it results in that noise (as exemplified by the "send chat message" case). Or for some reason, it can also result in all Skype sounds being muted, and on second try in that noise (as exemplified by the phone call example; it's really due to the notification sounds played at the start of the phone call, since there is no such problem when disabling the notification sounds).

So, the third workaround above works by letting Skype try (creating the noise), but muting that noise away (before or afterwards). As Skype's attempt to write to the channel never returns, it is blocked and Skype has to use a different (newly created) channel for the notification sounds when starting a phone call, as can be seen in the "Applications" tab of Gnome sound settings. That might be why now, playing the notification sound no longer results in corrupted audio. That indeed Skype tries permanently to write to the System Sounds channel (and only creating noise doing so) can be recognized from the fact that the noise stops when Skype exits: then, at last, it stops its desperate attempts of writing to System Sounds.

Other Issues: Silent Input and Output

Muted input. For some reason, at times it happens that Skype shuts off the microphone input when exiting. (This is possibly related to letting Skype access ones input mixer levels in its options dialog.) It can be fixed by going into the Gnome Sound Settings dialog, to tab "Input", and switching "Input volume" off and on again. When you see the input level bar moving when sound is present, all is well again.

Muted output. In other cases (as seen above), Skype output might be completely muted, while still working for other applications. Playing any sound from another application will fix this. And probably, going to Gnome Sound Settings and switching "Output volume" off and on again will also help.