Sound Problems/zh-tw

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理解音效

為了理解KDE的音效，你必須了解Linux聲音系統（這個章節假定你是在Linux上跑KDE）。有兩種類型的聲音系統運行在Linux上： ALSA和OSS。兩者都提供他們自己的聲卡驅動。 ALSA只能在Linux上用，OSS可以在多種UNIX系統上用。 ALSA允許多個程序同時訪問聲卡，OSS 不行。 OSS提供一個設備來輸出聲音。這個設備在一個時間只能被一個程序訪問。為了減少混亂，ALSA模擬了OSS，也提供一個設備作為聲卡的接口。通常ALSA和OSS一樣將聲卡的設備命名為/dev/dsp。在某些發行版中用的PulseAudio，提供了上述那些之上的另一層（layer）。它的任務是處理多個音頻流，以便，舉個例子，你可以在聽音樂的同時接受到消息通知。

Usual sound problems are

You cannot play sound because you are using an application that tries to access the sound device /dev/dsp, but this device is already in use by another application.
You cannot use the system-wide mixer kmix to adjust the volume of an application using the sound device /dev/dsp.
Different applications play sound using different devices.

Solutions: There is no silver bullet solving all your sound problems. The solution depends on the application you use to play sound. As an example, you can use mplayer with ALSA and OSS. For more info, see mplayer's documentation by calling

mplayer -ao help

Here are some specific issues that you may meet.

KDE 4 uses the wrong sound device.

That is not an error, but a configuration issue. To tell KDE 4 which soundcard to use (or prefer if available), open System Settings and go to Multimedia in the General tab.

Devices from /etc/asound.conf or ~/.asoundrc are not listed.

Phonon uses a function introduced in ALSA 1.0.14 to find those devices. To make this function list your entry you need to add a name hint. E.g.

hint {
     show on
     description "Name to display for the device"
 }

Here is a complete example that adds a new volume control named Phonon to your mixer:

pcm.softvolPhonon {
     type softvol
     slave.pcm "default:CARD=0"
     control {
         name "Phonon"
         card 0
     }
     min_dB -51.0
     max_dB 0.0
     resolution 100
     hint {
         show on
         description "My Soundcard with extra Volume Control"
     }
 }

After an update, PulseAudio gives you very low volume

PulseAudio has a 'normaliser' function which can cause this. To turn it off, set flat-volumes = no in /etc/pulse/daemon.conf

You are using KDE 3 and you keep losing sound. Sometimes it works, sometimes it doesn't.

KDE 3.x uses the aRts sound system. In earlier versions there were a number of problems, but in recent years the only problem remaining seems to be that aRts hangs on to the sound system when it has finished with it. To cure this, use kcontrol -> Sound & Multimedia. Towards the bottom of the General tab there is a setting for Auto-suspend if idle after: Set this to 1 second.

You have multimedia keys but KDE doesn't recognise them

This link has a clear description of what one user did to make his Volume-up and Volume-down keys work.

You tried all of the above but it still doesn't work (Ubuntu variants only)

Try replacing your sound card. If you still don't hear sound, check out this Ubuntu Community page