Example audio line¶

Objective¶

This wiki page demonstrates how to verify that the audio out and audio in lines are working.

Prerequisites¶

• Audio speaker or stereo headphones with a 3.5mm plug in order to listen to the audio
• Audio stereo cable with 3.5mm plug at both ends (or a microphone with a 3.5mm plug)
• Locate the audio sockets on the dev-kit.
  

Steps¶

Audio Out

• Enter the following commands to adjust the output volume
  

  amixer set PCM 100%
  amixer set 'Line DAC' 100%
  

• Plug the speaker or headphones into the Stereo Out socket.
• Enter the following command to play a 440 Hz tone which alternates 5 times between the left and right channels
  

  speaker-test -c2 -f440 -t sine -l 5
  

• You should hear a tone which alternates between the left and right speakers or the left and right sides of the headphones. If you only have a mono speaker, then you will just hear a steady tone.

Audio In

• Enter the following command to adjust the input volume
  

  amixer set PGA 100%
  

• When using a stereo audio cable
  • Plug one end of the cable into the Stereo Out socket and one end of the cable into the Line In socket.
  • Create two terminal windows into the device (use the serial console and an ssh connection or 2 ssh connections)
  • In one terminal enter this command
    

    speaker-test -c2 -f440 -t sine -l 5
    

  • In the other terminal enter this command
    

    arecord -f dat test.wav
    

  • When the speaker-test command finishes, hit ctrl-C in the second window to stop the arecord.
  • Remove the cable from the Stereo Out socket and insert the speaker or headphones
  • Enter the following command to playback the recorded audio
    

    aplay test.wav
    

  • You should hear the tone that was generated by the speaker-test command.
    • Note 1: While the speaker-test command alternated between left and right so you could hear the individual channels, the recording through the Line In seems to be turned into a mono signal so there isn't any alternating between the channels in the recorded wav file.
    • Note 2: While 100Hz tones can be heard from speaker-test in the speakers, a 100Hz tone does not seem to be recorded when using an audio cable. 440Hz tone is ok, but not the 100Hz tone.???
• When using a microphone.
  • Start recording using this command
    

    arecord -f dat test_mic.wav
    

  • Say something deep and profound
  • Hit ctrl-C to stop the record.
  • Connect the speaker to the Stereo Out socket.
  • Use the following command to play the recording
    

    aplay test_mic.wav
    

  • You should hear your recorded message

Conclusion¶

This wiki page has demonstrated how to verify that the Stereo Out is working and then how to make a recording from the Line In and play it back.