I am working on Linux ALSA. In my alsa.conf configured as file:
defaults.pcm.card 0
defaults.pcm.device 0
This card and deviece (0,0) refers to NVIDIA sound card HDMI out and I never used normally. In addition, when I use aplay with hw:0,0 option, I never have heared any sound. This is expecting situation. But when I use aplay wtih -D default option, I hear a music at my headphone. Normally, PC's analog output is connected to sound card 1. Why I can hear a sound my headphone although system default sound card card 0 in alsa.conf file?
These settings give the default values when you use hw instead of hw:x,y.
But the default device likely refers to PulseAudio or PipeWire, which have their own configuration.
Add the -v option to aplay to find out.