Tutorial - Recording Computer Playback on Linux
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PulseAudio
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 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.
- 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 audio interface.
- 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:
- 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. Do not 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 .
For a detailed description using Ubuntu 10, see Stereo Mix with Ubuntu 10 on the Audacity wiki.
JACK
Jack Audio System is commonly used in Linux distributions that specialise in media creation such as Ubuntu Studio and Studio 64.
To use Audacity with Jack it is useful or in some cases essential to have a few additional packages installed. This documentation assumes that you have Jack Audio System working on your machine. For help with setting up Jack, please consult the documentation for your Linux distribution.
Recording sounds playing from other applications is rather easy with Jack. Jack may be started using QjackCtl or from the command-line. If Audacity is launched after Jack is started then "Jack Audio Connection Kit" will be an available host option in the Device Toolbar. If Jack is started after Audacity has been launched then it will be necessary to for new audio devices before jack is available to Audacity.
Any Jack-compatible applications that are running before Audacity is launched will have their ports available in Device Toolbar. To make an application available to Audacity that is launched after Audacity it is necessary to use Rescan Audio Devices in the Transport Menu. After rescanning audio devices, input and output ports from other applications will be available in the Recording and Playback boxes in Device Toolbar.
In this image the output of Hydrogen drum machine is being selected as the recording source. This will enable Audacity to record directly from the audio output from Hydrogen. If "System" is selected as the recording source then Audacity will record from the physical audio interface input.
Applications that do not directly support Jack may also be used with Jack on a system that uses PulseAudio (such as Ubuntu and Debian based distributions) by installing "pulseaudio-module-jack". This provides the modules "Jack Source" and "Jack Sink" that allow PulseAudio to use Jack. For example, to record sounds playing through Firefox, PulseAudio Volume Control (pavucontrol) can be used to direct the output from Firefox to Jack Sink. The recording input for Audacity can then be set to record from "PulseAudio Jack Sink" and the sound will be recorded.
Other Methods
Alternative programs for recording computer playback
An alternative to recording streaming audio from the Internet is to download the data directly to disk, either by using command-line tools such as streamripper or mplayer, or with a browser plug-in (many available for Firefox), or writing the stream to disk from a media player such as VLC or xmms, or using a graphical down-loader such as streamtuner.
Use a loopback cable
This is a simple and effective method of recording what is playing on the computer. It has the disadvantage that the audio signal is converted from digital to analog, then from analog to digital, instead of staying in the digital domain. This may result in some slight increase in noise and distortion.
Plug your line-out or headphones-out to the line-in using a cable with a stereo mini-plug at each end, then record from line-in. To hear the sound while recording, use a single to double stereo connector to give you a jack for the speakers or headphones.
If you have only mic-in and no line-in is selectable through alsamixer, you can build an attenuator to reduce the line level output to a level suitable for mic-in. But probably this will only provide mono recording, because mic-in is mono in most cases. As well, the quality may be questionable.
