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What is JACK?

Jack is a low-latency audio server that can connect the input and outputs of a number of audio applications. It is different from other audio server efforts in that it has been designed from the ground up to be suitable for low-latency professional audio work.

An example of use, first start jack then start alsaplayer to play the stream (SomaFM radio, in this case) and thirdly, start ecasound to record directly in ogg format.

jackd -d alsa
alsaplayer -i text -o jack -s somafm
ecasound -i:jack_auto,somafm -o:somafm.ogg

Jack and audio mixing

Since jack was designed for professionals and low latency, by default it opens the first hardware device it find, usually "hw:0.0". Unlike most applictions, it does not automatically route thru dmix. This means that if you want to mix several audio streams in software for output, the streams must talk to jackd. To force jackd to use dmix instead, allowing other apps to function as normal (but adding latency to jack) it was suggested the following command be used:

jackd -d alsa -P defaultĀ :0

(This does not work on all systems)

How to use oss2jack and Skype

Salvatore Di Pietro \<salvuz_78 at virgilio dot it> explains: Well ,it's not that complicated... I went to\~kor/oss2jack/

downloaded and installed fusk-kor and oss2jack. I am on Slackware 10.1, which uses udev, so there were no problems with fusd. Now there's this little wrapper called skype_dsp_hijacker

that enables you to choose the /dev/dspXX to use for in put and /dev/dspYY to use for output (and /dev/mixerXX to be controlled by skype)Once installed, start jack, then

oss2jack -n 100


MICDEV=/dev/dsp100 \
SPEAKERDEV=/dev/dsp100 \
LD_PRELOAD=/usr/lib/ skype

and the trick is done!

More JACK-specific documentation in this Wiki

Retrieved from ""

Category: Software