By default, Line In is not enabled in Linux. To enable Line In, complete the following steps:
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Open a Terminal window and run alsamixer. This opens a window that allows you to change settings for each sound channel.
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Press the F4 key to change capture settings.
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- Use the left and right arrow keys to select capture channels.
- To enable input on a selected channel, press the spacebar. When enabled, CAPTURE is displayed in red. Adjust the gain for a combination of minimum noise and sufficient volume.
- Make sure the gain on Digital is a positive value. Increase the gain to a acceptable volume level.