I am attempting to eliminate possible poor electrical connections associated with the headphone socket by starting up the laptop from cold (literally having cooled down) and running a video to check the sound quality.
Last evening, within 10 minutes of starting the laptop from cold, the sound became crackly. I used the Test Sound button on the Sound panel and found no response from the Front Left Test button. However, the Front Right Test button caused a muted response from the left speaker! I did an immediated restart and everything then worked perfectly - no crackles and correct sound tests. This morning, after an overnight cold soak, the system started up and the speakers responded correctly to the Test Sound button. However, within 10 minutes of playing a video, the sound became crackly. The speakers responded correctly to the test Sound button and the crackles subsided. I plugged in a pair of headphones which caused the device identification panel (headphones, headset or microphone) to pop up. However, the sound was directed through the headphone straight away. On removing the headphones, the sound went back to the speakers without having to click their menu item in the Sound panel. (Has the system "learned" from previous connections?) After a further 20 minutes of playing the video, the sound became crackly again. The speakers did respond correctly to the Test Sound button but the crackles were still evident. I picked up the laptop and gently tapped the underside of the case near the headphone socket. This might have contributed to the crackling sound but it then disappeared and the speakers sounded normal again. By this time, the laptop had warmed up to its normal operating temperature. Since plugging in headphones seems to cause an interrupt that brings up the device select panel, there must be an electrical interface between the headphone socket and the circuit board. I doubt if the headphone socket is gold plated but intermittent connection must be expected with such an interface. Normally, when there is a connection between mechanical contacts and electronic circuits, some form of bounce suppression is employed. Apart from the early electronic calculators that used mercury wetted reed switches, it has been common practice to include this bounce suppression in the software. I am sure that this has not been overlooked in the Linux kernel but it might be prudent to ensure that such a bounce suppression is compatible with the cheap and chearful electrical contacts found on headphone sockets. (Software bouce suppression works well enough on keyboards. Perhaps the parameters used could be migrated to the headphone socket interface.) -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to alsa-driver in Ubuntu. https://bugs.launchpad.net/bugs/1402666 Title: [XPS13 9333, Intel Haswell HDMI, Digital Out, HDMI] Playback problem Status in alsa-driver package in Ubuntu: Incomplete Bug description: If an HDMI monitor is plugged into the video out and the Videos app is started, the Systems Settings > Sound > Output shows only the Speakers, Built-in Audio in the Play sound through listing. The HDMI option is not presented. The workaround is to open the VLC app which lists the Built-in Stereo (HDMI) option under its Audio > Audio Devices menu. When a video is started in VLC, having selected the HDMI option, the sound plays through the monitor speakers. The HDMI / Display Port , Built-in Audio item then appears in the Play sound through window, even though the selection highlight remains on Speakers. The sound output can be switched between either output by highlighting the chosen option. If VLC is closed and Videos is restarted, the sound now plays through the previously selected HDMI item and can be switched between the monitor and the laptop's speakers. What I regard as a bug is the failure of the HDMI option to appear in the Play sound through listing as soon as an HDMI monitor is plugged into the Display Port output. Obviously, VLC has the means to add this item but the Videos app does not seem to be able to do this by itself. In contrast, as soon as a previously paired set of Bluetooth headphone are turned on, the Headset does appear as a menu item in the listing. I would reasonably expect the plugging in of an HDMI monitor into the Display Port to automatically add this item as well as its affects on the Screen Display pane of Systems Settings. Note: the laptop is running Ubuntu 14.10 and the Linux kernel has recently been upgraded to v3.18 (Vivid). ProblemType: Bug DistroRelease: Ubuntu 14.10 Package: alsa-base 1.0.25+dfsg-0ubuntu4 Uname: Linux 3.18.0-031800-generic x86_64 ApportVersion: 2.14.7-0ubuntu8 Architecture: amd64 AudioDevicesInUse: USER PID ACCESS COMMAND /dev/snd/pcmC1D0c: david 2242 F...m pulseaudio /dev/snd/controlC1: david 2242 F.... pulseaudio /dev/snd/controlC0: david 2242 F.... pulseaudio CurrentDesktop: Unity Date: Mon Dec 15 13:13:47 2014 InstallationDate: Installed on 2014-12-11 (3 days ago) InstallationMedia: Ubuntu 14.04.1 LTS "Trusty Tahr" - Release amd64 (20140722.2) PackageArchitecture: all ProcEnviron: LANGUAGE=en_GB:en PATH=(custom, no user) XDG_RUNTIME_DIR=<set> LANG=en_GB.UTF-8 SHELL=/bin/bash SourcePackage: alsa-driver Symptom: audio Symptom_AlsaPlaybackTest: ALSA playback test through plughw:HDMI failed Symptom_Card: Built-in Audio - HDA Intel HDMI Symptom_Jack: Digital Out, HDMI Symptom_Type: None of the above Title: [XPS13 9333, Intel Haswell HDMI, Digital Out, HDMI] Playback problem UpgradeStatus: Upgraded to utopic on 2014-12-11 (3 days ago) dmi.bios.date: 09/11/2014 dmi.bios.vendor: Dell Inc. dmi.bios.version: A05 dmi.board.name: 0D13CR dmi.board.vendor: Dell Inc. dmi.board.version: A00 dmi.chassis.type: 8 dmi.chassis.vendor: Dell Inc. dmi.chassis.version: 0.1 dmi.modalias: dmi:bvnDellInc.:bvrA05:bd09/11/2014:svnDellInc.:pnXPS139333:pvr:rvnDellInc.:rn0D13CR:rvrA00:cvnDellInc.:ct8:cvr0.1: dmi.product.name: XPS13 9333 dmi.sys.vendor: Dell Inc. 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