Ardour has a lot of features that are going for it. However, one of the most valuable is the fact that a channel or bus can have a different number of inputs and outputs. This is very useful in cases where an effect plugin performs some asymmetrical task, such as sidechain compression, or a stereo-to-mono mixdown.
The Channel Control Window
In order to make changes to the number of inputs and outputs in a single Ardour track or bus, you need to access the Channel Control window. This is accessible through the appropriate channels button in the mixer strip for that track/bus.
On the right is the top and bottom parts of your typical Ardour mixer strip. The channel manager buttons are the ones highlighted in red and green; the green button controls the number of inputs and their connections, and the red button determines the number of outputs and their connections.
Once you click on those buttons, you will see a drop-down menu appear, consisting of “Edit,” A number of “In” or “Out” buttons (depending on which one you pressed), “Master Out,” (If you are using the bottom one), and “Disconnect.” The editor allows you to have fine control over the track/bus, including the channel makeup, so we will select “Edit.”
Once in the channel editor window, you will see the following (adjusting for the initial number of channels and the direction of the connection):
On the left is the track’s channel controls, and the right shows the connection selection dialog. If you’re like me, and you set Jack to refuse self-connection, the right part will not actually do anything… that’s Ladish‘s job. However, the left part will allow you to determine how many input (or output) jacks that this specific track will have.
This specific track is one I use with the Jack-Alsa Bridge to bring Skype into the connection graph; I am also making an article on recording, processing and submitting a podcast to Libsyn, which will come in the next couple weeks, and this is one of the components in the workflow. The Jack-Alsa Bridge is, regardless of the source program, always a stereo connection. However, when recording podcasts, we want the output to be a mono connection.
Modifying the number of tracks in this window is extremely easy: Simply click “Add” or “Remove.” For every time you click “Add,” a new channel is created for this track, and for every time you click “remove,” the last channel is removed from this track. In this case, we’re adding and removing inputs. So, if I click “Add,” Another one will appear:
As you can see, we now have three channels on the left instead of two, and it is immediately reflected in the Gladish window (or other Jack Connection graph program).
You will note that the Additional input appeared after the first output, instead of after the first two “Skype Bus/in” ports. This is because Gladish always places new items at the end of the box’s list. However, the next time Ardour is started, this will be corrected:
Now, if I were to click remove twice…
We’re now left with only one input.
You can do the same with the outputs as well.
This process is especially useful when taking a mono signal in, say from a voice or electric guitar, and panning them in a stereo field (or even a surround soundfield!) In fact, the number of inputs and outputs will change the way the mixer strip’s panning controls look:
The first box is blank, because the track is a completely monaural track; there is only one channel going in and out.
The second track has a single input channel and a stereo output. In this case, you can move the green line in the box to determine where the sound will be heard in the stereo field.
The third has a stereo input and a stereo output; each of those boxes identify where the input’s channel will appear in the output’s soundfield; this is very useful when reducing the stereo field’s width, or when you need to reverse the channels. As you can see, the first channel is all the way to the left, and the second channel is all the way to the right, which essentially means that the first channel is the left channel, and the second is the right channel. If they’re not left and right, but two monaural channels, you can move those green lines to the center, or perhaps slightly off-center in order to give the sensation of the two channels being in different locations in front of the listener.
Finally, in the fourth, you have a situation with three inputs and four outputs. In this case, the inputs and outputs can be arbitrary, except that they each must be three or more. The positions of the blue numbered dots determines the location of each of the input channels, while the orange dots determine the positions of the speakers. You can use the mouse to drag them around until you have your desired locations.
Plugin Usage of Channels
When opening plugins, you will see the number of channels a given plugin expects in the plugin manager. Use this to determine what the best number of channels are for a specific track.
Do you see the “# Inputs” and “# Outputs” columns? These tell you what the plugin in question expect.
For example, the crossfader expects four inputs (for two stereo signals to fade between), and two outputs (for the final stereo signal to be sent out).
On the other hand, the Ambisonic B-Format encoder expects a single channel, and sends out 4 channels as a result… although keep in mind, these are specially formatted, and should only be mixed and panned with Ambisonic plugins.
As a side note, Ambisonic is a surround-sound technology that uses a specially-formatted group of signals to determine the exact angle from which a sound is coming in a soundfield, regardless of the speaker configuration. We’ll go into depth in a future article on Ambisonics (preferably once I have the money and space for a surround sound speaker system). Since the 4 channels are specially formatted (Omnidirectional, X-Axis Figure-8, Y-Axis Figure-8, and Z-Axis Figure-8), they should only be mixed with other Ambisonic B-Format channels of the same type.
Well, in this article, we covered the use of channels in Ardour, and the way they can be added, removed, and panned. We also covered the basics of determining what channel configurations are expected from plugins used in Ardour. Hopefully, now that you have a better understanding of Ardour’s channel management features, you can be better-positioned to use them to make something good!