ALSA or JACK?

[worldofchico]

Newbie question, but googling hasn't quite answered it for me ...

If I have a low spec netbook, and I intend to simply use it with MIXXX to play tunes out through a Hercules Mk2 live, should I use ALSA or JACK as the sound driver in MIXXX?

Up till recently I thought I could theoretically squeeze more performance out of it using Jack (with ALSA as the backend), with a realtime kernel, and using the rtirq script, pasuspender to start JACKd, chrt to up process priority etc. But am I wrong?

Should I only be using JACK if I need to route the audio to another audio app, or control something with a midi device? I don't need to do either. I just need to play tunes in MIXXX and control MIXXX using the Hercules Mk2. Will I get the same performance simply using an ALSA driver?

I ask because ALSA seems to give less crackles and breakups than using JACK, although I think i'm misconfiguring something in JACK. But I wonder if I'm making this more difficult than it needs to be .... help?

[t-mo]

I may be wrong but as far as I know, does JACK not increase the latency, only takes some more CPU-power. But it is not making the latency lower. So if you want to use it on a low-spec Netbook you better save some processing power to prevent crackles, I guess.

[mrthraz]

taken from the jackaudio.org site:



"JACK is system for handling real-time, low latency audio (and MIDI). It runs on GNU/Linux, Solaris, FreeBSD, OS X and Windows (and can be ported to other POSIX-conformant platforms). It can connect a number of different applications to an audio device, as well as allowing them to share audio between themselves. Its clients can run in their own processes (ie. as normal applications), or can they can run within the JACK server (ie. as a "plugin"). JACK also has support for distributing audio processing across a network, both fast & reliable LANs as well as slower, less reliable WANs.

JACK was designed from the ground up for professional audio work, and its design focuses on two key areas: synchronous execution of all clients, and low latency operation. More background information is available."


so jack is defiantly low latency, but i can't say if it will help processor power.

[mrthraz]

also from the site:


Doesn't use JACK add latency?

There is NO extra latency caused by using JACK for audio input and output. When we say none, we mean absolutely zero. The only impact of using JACK is a slight increase in the amount of work done by the CPU to process a given chunk of audio, which means that in theory you could not get 100% of the processing power that you might get it if your application(s) used ALSA or CoreAudio directly. However, given that the difference is less than 1%, and that your system will be unstable before you get close to 80% of the theoretical processing power, the effect is completely disregardable.