Translations:ALSA/110/en
From Gentoo Wiki
Those who want to try JACK must know one thing: You will need a realtime kernel and rt operations only if you want to make a Digital Audio Workstation (DAW) with your computer, which necessitate something pulseaudio is not able to achieve: constant sound latency as low or lower than 20 msec (pulseaudio is not able to provide constant sound latency at all), and synchronous operations. JACK can also be an alternative to pulseaudio for an user that want a professional solution, see JACK#ALSA - Bridging ALSA and JACK together.