3.5mm Audio Jack

Please note: since the original Pi B+ version, the 3.5mm jack on the Raspberry Pi is not dedicated to audio alone. The jack is 4-pole (3 rings or tip, ring, ring, sleeve - TRRS) audio / video jack. This is explained in detail at the Raspberry Pi Spy site.

If using the Raspberry Pi 3.5mm jack to output sound into your car's aux (auxiliary) input socket (if your car has one), sound quality can be improved by adding the following line to your boot/config.txt file:

audio_pwm_mode=2

This enables the 7bit, 781kHz audio driver released in 2016. Compared to the much-maligned original 11bit, 48kHz driver you should notice the difference ;)

More details are available on the Raspberry Pi forum.