Ubuntu 20.04系统下Line-in无声音问题求助

Hey there, let's work through this line-in audio issue together—no need to worry, it's almost always a simple setting tweak rather than a complicated problem!

First, let's clear up why your party speaker works but your Ubuntu PC doesn't: the speaker has super straightforward input logic—once it detects an audio cable, it immediately routes that signal to the speakers. Your PC's audio system (PulseAudio/ALSA) has more layers: default device selection, volume controls, mute states, and signal routing rules, so it's easier for a setting to be off without you noticing. It's not that the computer is "worse"—it just has more configurable options!

Now let's go through the fixes step by step:

• Double-check PulseAudio Volume Control settings
  Open pavucontrol and switch to the Input Devices tab. Find your "Line-in" device:

  1. Make sure the volume slider isn't dragged all the way down.
  2. Click the green checkmark next to it to set it as the default input device—sometimes the system sticks with the built-in mic even if line-in is plugged in.
  3. Ensure the "Mute" checkbox isn't ticked.

• Verify system sound settings
  Open your system Settings > Sound, go to the Input tab. Confirm that "Line-in" is selected as the active input device, and adjust the input volume to a reasonable level (not muted).

• Test with command-line tools to rule out hardware issues
  Open a terminal and run this command to record a 5-second sample from line-in:

  arecord -d 5 test_linein.wav
  

  Play it back with:

  aplay test_linein.wav
  

  If you can hear the audio, that means your hardware is working and it's just a setting issue. If not, move to the next step.

• Check ALSA mixer settings
  Run alsamixer in the terminal. Press F4 to switch to the Capture (input) view. Look for the "Line" or "Line-in" channel:

  • Use the arrow keys to select it, then press M to toggle mute (you'll see "MM" turn to "00" when unmuted).
  • Use the up arrow to increase the capture volume to around 70-80%.

Most of the time, one of these steps will get your line-in working. It's not as "plug-and-play" as a speaker, but it's definitely manageable!

备注：内容来源于stack exchange，提问作者fugee ohu