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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.

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