JACK

JACK is an audio server daemon (service) that allows low latency connection between so-called "jackified" applications. Both audio and MIDI data can be transmitted.

Jack can work with ALSA, PortAudio, CoreAudio, FreeBoB, FFADO and (in test mode so far) OSS.

Suppose we need to record a multi-channel composition with vocals and synthesizer as instruments. We have a MIDI keyboard, a software (virtual) synthesizer on the computer, and a microphone connected to the sound card input. For some reason we want to record both tracks at the same time. Then, with the JACK, we can connect:

• MIDI keyboard to the virtual synthesizer;
• the sound output of the synthesizer to the audio card (to hear what we play);
• the sound output of the synthesizer to the corresponding track of the recording program;
• the audio input of the audio card (where the microphone is connected) to the corresponding track in the recording software.