PCM Audio Out
To enable the PCM audio output add the below lines to /boot/config.txt
# Enable audio (loads snd_bcm2835 in OS) dtparam=audio=on dtoverlay=pwm-2chan,pin=40,func=4,pin2=45,func2=4
You may find you can improve the audio quality by adding the below line in addition to the above :
audio_pwm_mode=2
if you then run the below command from the comand line this will run a basic test on the output
# amixer sset "PCM" 95% # speaker-test
Note that the PCM output audio requires additional amplication to drive anything other than a basic set of headphones
The below links are useful as a reference :
https://learn.adafruit.com/adding-basic-audio-ouput-to-raspberry-pi-zero
https://learn.adafruit.com/adding-basic-audio-ouput-to-raspberry-pi-zero/pi-zero-pwm-audio