运行audacity后，点击录音，居然什么声音也没录下来，看来得配置一番
中文资料太少，看官方帮助文档也是办法之一。
以下是摘录：网址是http://manual.audacityteam.org/o/man/tutorial_recording_computer_playback_on_linux.html
PulseAudio is a sound server providing professional audio features such as mixing and input/output routing. It is the default audio device on many Linux distributions including Ubuntu, Linux Mint, Open Suse and many Debian/Ubuntu-based distributions. PulseAudio operates as a proxy between sound applications and the audio hardware (usually via ALSA). PulseAudio Volume Control provides a "Monitor" device which listens for the audio output of other applications such as Firefox or Rhythmbox. Setting PulseAudio Volume Control to capture from the Monitor device lets Audacity record computer playback when its input device is set to pulse.
好吧，现在大家电脑的发音都通过pulseaudio了，它还有个控制程序叫PulseAudio Volume Control (pavucontrol) ，默认没安装，ubuntu源里有，要先安装它！
啥？不懂？
pulseaudio是相当于一个中间代理（声卡硬件到播放器之间的）
PulseAudio Volume Control 提供了一个“监视”设备用来监听各种音频播放器（像firefox播放youtube，audacious , Rhythmbox等等）的音频输出。
我的电脑上有realtek892声卡和hdmi两个音频输出，其中hdmi的被我禁用了，我用892的发声的。在我的系统里，声卡892被识别成“内部音频模拟立体声”。请看下图
If not already installed, add PulseAudio Volume Control (pavucontrol) to your system. This is usually available in the distribution's repository.
Ensure that PulseAudio is running. In Audacity's Device Toolbar, set the Host to ALSA and the recording device to pulse.
On systems where PulseAudio is the default sound system the recording device may be set to default.
Audacity's playback device may be set to pulse or to any available soundcard.
Pulse-device-toolbar.png
Ensure that "Software Playthrough" is not enabled in the Transport Menu then left-click on the Recording Meter to turn monitoring on.
Open PulseAudio Volume Control and choose the "Recording" tab.
In the "Capture from" dropdown, select the "Monitor" option of the playback device used by the application you want to record from, as shown below:
Pavucontrol-CaptureMonitor.png
Launch the application that you wish to record and begin playback.
In the "Recording" tab of PulseAudio Volume Control, drag the volume sliders so that the recording level in Audacity's Recording Meter is to left of 0 dB (-6 dB is a good level to aim for).
The playback level of the application being recorded will also affect the level of the recording. Use the "Playback" tab in PulseAudio Volume Control or the volume control in the application to adjust the output level.
If you want to record without hearing the audio, you can turn down the Audacity playback slider or turn down the sliders on the Output Devices tab of PulseAudio Volume Control. Don't use the Mute button in PulseAudio Volume Control, because this will cause Audacity to record silence. You can also set the port on the Output Devices tab of PulseAudio volume control to the audio output such as "headphones" but not connect any headphones or speakers to the port.
When the recording level has been correctly adjusted, press the Record button in Audacity .
