Select the system default audio device
You can set the system default audio device by following the steps below.
Use the following command to view all the sound card devices in the system (Note: different development boards will have different results):
pi@NanoPi:~$ aplay -l **** List of PLAYBACK Hardware Devices **** card 0: realtekrt5651co [realtek,rt5651-codec], device 0: ff880000.i2s-rt5651-aif1 rt5651-aif1-0  Subdevices: 1/1 Subdevice #0: subdevice #0 card 1: rockchiphdmi [rockchip,hdmi], device 0: ff8a0000.i2s-i2s-hifi i2s-hifi-0  Subdevices: 1/1 Subdevice #0: subdevice #0 card 2: ROCKCHIPSPDIF [ROCKCHIP,SPDIF], device 0: ff870000.spdif-dit-hifi dit-hifi-0  Subdevices: 1/1 Subdevice #0: subdevice #0
As you can see, the following sound card devices are available on the hardware:
Sound card device Sound card number Description realtekrt5651co 0 Realtek sound card's default output interface (through 3.5mm jack interface) rockchiphdmi 1 HDMI ROCKCHIPSPDIF 2 SPDIF (Note: temporarily unavailable, because the hardware is not exported)...
To configure the audio output to the 3.5mm jack, modify the configuration file /etc/asound.conf and modify it to the following:
defaults.pcm.card 0 defaults.pcm.device 0
To configure to output audio to HDMI, change the defaults.pcm.card above to 1.
Note that some boards do not have a Realtek sound card (no 3.5mm jack interface), so the card number of the HDMI device will be 0, so the configuration should be based on the result of the aplay -l command.