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 85%
  amixer set 'Line DAC' 85%
  

• 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 30%
  

• When using a stereo audio cable
  • Enter the following commands to work with something like a loop-around cable.
    

    amixer sset 'Left PGA Mixer Line1L' off
    amixer sset 'Right PGA Mixer Line1R' off
    amixer sset 'Left PGA Mixer Mic2L' on
    amixer sset 'Right PGA Mixer Mic2R' on
    

  • 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.
• When using a microphone. CAUTION : See Mic In below.
  • Enter the following commands to work with a microphone.
    

    amixer sset 'Left PGA Mixer Line1L' on
    amixer sset 'Right PGA Mixer Line1R' on
    amixer sset 'Left PGA Mixer Mic2L' off
    amixer sset 'Right PGA Mixer Mic2R' off
    

  • 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

Mic In¶

The devkit has connected the audio input as a Stereo Line In instead of a Mic In. In order to use the port as a Mic In, a board modification would be required.

Devkit:

According to the TLV320AIC3104 EVM Users Guide, to support a stereo mic in on IN2, it should be hooked up like:

Depop R226 and R227 and connect to MICBIAS using separate 2.2k resistors. This should create a working 2-channel mic input.
Though to fully match the EVM schematic, R222/R223 should be 0hms and C128/130 should be 0.1uF.

Note: It may be necessary to alter the alsamixer settings as well as the simple-audio-card routing in the device tree.

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.