JACK sound server and Routing Audio Tracks in Ardour

This tutorial will help you to get started with Ardour in Linux. Two topics will be discussed namely the role of JACK in Ardour and knowing the basics of audio routing.

Importance of JACK sound server

First, you need to know a few important things before you start doing recording, mixing and mastering projects with Ardour. This software utilizes JACK, an audio connection kit which is essentially a sound server that you can use to record with as much as low latency as possible. Low latency is important for professional music production and JACK is the tool to do this.

Without JACK, no dedicated resources (memory and CPU) in real time that can be utilized by Ardour. The result is that during actual multitrack recording session, your tracks will begin to slow down and experience delay/latency or lag. During installation of Ardour, you already configured JACK to operate in real time as needed. This implies that whenever Ardour is running, it connects to JACK that will dedicate a substantial amount of computer system resources for optimal operation.

Second, Ubuntu runs on PulseAudio sound server by default which is essentially the reason why you will be able play music by default. When you start Ardour and JACK; the PulseAudio will shutdown itself. Unless with some configuration; you will not be able to listen to your Linux default music player and other players unless JACK is properly configured to accept PulseAudio streams.

Do not confuse with the differences between ALSA, PulseAudio and JACK or even FFADO. They are all different. ALSA is a generic sound driver that communicates directly with your sound device/hardware (except for Firewire audio interface which are handled by FFADO). PulseAudio is a sound server that interacts with a variety of software in your operating system that utilizes audio (such as Rhythmbox, your browser etc). JACK is also a sound server similar to PulseAudio only that it provides “low latency” operation suitable for music production.

Start and Turning off JACK

Opening an Ardour session will start the JACK server. Or you can type “qjackctl” (without quotes) in terminal and click “Start”. The objective of starting JACK is to have no errors and almost negligible XRUNS. Encountering serious error or JACK failed to start means a problem with your audio device, JACK installation etc. Read step 4C of this tutorial for details about starting JACK. To lower the XRUNS or to make it stable, you need to properly assign some settings on your JACK. This can be done by clicking the SETUP. For example, below is a stable JACK settings for a Firewire audio interface (Saffire Pro40) playback (not recording):

JACK optimal settings might differ for every audio interface and system, so you need to tweak a lot. You can read step3 of this tutorial for more tips on configuring JACK for more stable operation.

To stop JACK server, simply click the stop button. Below is the screen shot of the JACK GUI when it is turned off:

When JACK is off, you can resume using PulseAudio sound server for normal audio applications.

Routing Audio Tracks to Master Channel

This section will illustrate one of the most important functions in Ardour mixing –routing audio tracks. When you launch Ardour, at first there is only one channel that appears. This is called a “Master” channel, see below:

This master channel will combine all audio in the multitrack environment and then output a “Master” stereo track (left and right channels). The audio inputs to “Master” channel could be any track or bus (e.g. the bass guitar, drums, vocals, or existing recordings in your drive). The difference between “track” and “bus” is that “bus” takes input from outside Ardour (like when you are recording using your computer hardware audio interface). “Track” can be used to load audio which are already recorded (example from Tape source or previous recordings save in your hard drive). Track and bus can be overwritten or altered by re-recording. Both are treated equally by Ardour and can use plugins , etc. It could also be a mono (one-channel) or stereo (two-channels) based audio. Supposing you are doing multi-track work of a stereo recording of bass guitar and kick drum track. The input-output diagram to “master” channel are as follows:

Discussion: In Ardour, the master channel accepts two unique inputs: In1 and In2. For example, to input the bass guitar stereo audio you need to route Out1 of bass guitar to In1 of Master Channel and then Out2 of Bass guitar to In2 of Master Channel. The master channel then combines all signals found on its input and then route it to Out1 and Out2 for playback. This is the one you can listen in your studio monitors. Out1 and Out2, specifically are outputs of your audio device or soundcard. So how can you actually route audio tracks in Ardour environment? This is the time you will be using the “Show Mixer” feature (Go to Window – Show Mixer). This is how it looks like:

In the above mixer, there are two track inputs, namely the “kickdrums” and “chorus bass”. On your right you will see the “master” bus. To edit the master bus input, simply click the number below the word “master” (which is 4 shown in the screenshot above) and then click “Edit”. Why the number is shown as 4? It is because since there are two stereo track inputs (bass and kick drums), all in all there are 4 mono inputs to the master channel (Bass guitar out 1, Bass guitar out2, Kick drum out 1, Kick drum out 2). After you click “Edit”, you will see the following:

The input tracks shown under “Master Input” is exactly the same as depicted on the input diagram shown earlier. Under “Available Connections” there are two tabs: “Ardour” and “System”. Ardour tabs means that it shows connections that are only available inside Ardour environment. Example of these connections are: kickdrum/out 1, kickdrum out2, chorus bass/out 1, chorus bass/out 2, etc. “System” connections are those found outside the Ardour environment. Example of these connections: “Capture_1” and “Capture_2”, these are inputs coming from your soundcard for example. To add inputs to In1, simply click “In1” tab and then click which connection you would like to add either in “Ardour” or “System” based connections. Do the same for In2. To remove inputs, just click the track input under In1 or In2. Now you are familiar with the Master Input, close this window and then go to Master Output. This looks similar to Master Input only that it shows all possible output connections:

In the master output, since you would like to monitor the playback to check how your mix should sound like, the output is then routed to “system:playback_1” and “system:playback_2”. These are soundcard outputs which is then feed to your studio monitors. These are basic Ardour routing techniques which of course can well be extended to your other tracks, busses, etc aside from routing to master channel.

Content last updated on June 27, 2012