Audio

This chapter describes the common information and instructions of Audio on IoT Yocto, such as listing the audio hardware, using a USB audio device, and so on. Audio on different platforms may have some platform-specific instructions or test results. For example, you will have different audio interfaces on different platforms. Please refer to the platform-specific section for more details.

Note

All cmd operations presented in this chapter are based on the IoT Yocto v22.1, Genio 350-EVK. You might get different operation result depends on what platform you currently use.

ALSA 

The implementation of the audio driver follows ALSA project. You can use aplay and arecord to list available sound devices.

aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: mtsndcard [mt-snd-card], device 0: MultiMedia1_PLayback (*) []
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: mtsndcard [mt-snd-card], device 1: MultiMedia2_PLayback (*) []
  Subdevices: 1/1
  Subdevice #0: subdevice #0

arecord -l
**** List of CAPTURE Hardware Devices ****
card 0: mtsndcard [mt-snd-card], device 2: DL1_AWB_Record (*) []
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: mtsndcard [mt-snd-card], device 3: MultiMedia1_Capture (*) []
  Subdevices: 1/1
  Subdevice #0: subdevice #0

You can find the corresponding device nodes under /dev/snd/.

ls -l /dev/snd
total 0
drwxr-xr-x 2 root root       60 Jan  1  2010 by-path
crw-rw---- 1 root audio 116,  6 Jan  1  2010 controlC0
crw-rw---- 1 root audio 116,  2 Jan  1  2010 pcmC0D0p
crw-rw---- 1 root audio 116,  3 Jan  1  2010 pcmC0D1p
crw-rw---- 1 root audio 116,  4 Jan  1  2010 pcmC0D2c
crw-rw---- 1 root audio 116,  5 Jan  1  2010 pcmC0D3c
crw-rw---- 1 root audio 116, 33 Jan  1  2010 timer

The default hardware controls are set according to /var/lib/alsa/asound.state. You can use alsactl to store and restore the state.

alsactl restore   # Restore file to state
alsactl store     # Store state to file

There are some default plugin devices specified in /etc/asound.conf. Please refer to Asoundrc for more details. For example, the following configuration creates an alias name, jack_speaker, which represents /dev/pcmC0D0p. Then, you can play the music with the name jack_speaker by aplay -D jack_speaker.

pcm.jack_speaker {
       type plug
       slave {
               pcm "hw:mtsndcard,0,0"
               channels 2
       }
}

For the examples of playback and capture, please refer to each platform section.

USB Audio 

On IoT platform, it supports USB audio. You can simply plug in a USB audio device (e.g. USB headset) and check its ID and name before playing or recording something.

aplay -l
**** List of PLAYBACK Hardware Devices ****
card 1: H540 [Logitech USB Headset H540], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

arecord -l
**** List of CAPTURE Hardware Devices ****
card 1: H540 [Logitech USB Headset H540], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

You can see there is card 1 with the CAPTURE device and the PLAYBACK device.

To play the music:

aplay -D hw:1,0 sample.wav

To record the voice:

arecord -D hw:1,0 -r 48000 -f S16_LE -c 2 sample.wav

Audio

ALSA

USB Audio

ALSA 

USB Audio 