Creating a Document

In AU Lab, every document that you create is associated with a specific Audio Device on your system. When creating a document, you specify the input and output track configurations as well as specify the speaker layout using the Document Configuration Assistant dialog. To create a new document, choose New from the File menu.

Using the Document Configuration Assistant

The Document Configuration Assistant leads you through the steps necessary to configure a document. This includes the input and output configurations, the specification of a multichannel layout if a multichannel output track is used, and the selection of the audio device. For convenience, common document configurations can be saved and used as the basis of a subsequent document. See Saving Configurations for additional information.

Configuring Outputs

The first step in creating a document is specifying the configuration of the outputs. The document must contain at least one output and may consist of one or more channels.

At the top of the dialog is a diagram that shows the visual representation of the configuration of the document's output tracks. As shown by the image (below), the default output configuration is a single stereo output track.

You may add additional output channels by clicking on the Add Output button.

You can change the number of channels for a selected track by choosing the number of channels from the Output Channels popup menu. There are three choices- Mono (1 channel), Stereo (2 channel), or Multichannel (more than two channels). If you select Multichannel, you will be able to specify the number of channels and the layout of the speakers. See Specifying the Multichannel Configuration for additional information.

You can delete an existing track by clicking on the track in the configuration diagram, or select the track from the Selected Output popup menu and then click the Remove Output button. Note that you must always have at least one output track, so it is not possible to remove the last track in the output configuration.

The following image shows an output configuration with a 6 channel output track followed by a stereo output track. The stereo track is selected.

Specifying the Multichannel Configuration

When a multichannel track is created, the Document Configuration Assistant expands, showing additional options for specifying the channel layout. Note that there can only be a single multichannel format per document. If multiple multichannel output tracks are created, they will both use the same layout.

These new controls include a Channel Configuration popup menu for specifying the configuration type, as well as a graphic representation of the speaker layout and an area for additional customization based on the configuration type.

There are three supported configuration types in AU Lab:

Constrained

The constrained multichannel configuration type is a speaker layout consisting of 3 or more speakers arranged in an arc in front of the listener. Each speaker is spaced equally, and the first and last speaker define a spanning angle. After selecting this configuration from the Channel Configuration popup menu, the editor will display two additional text fields for editing the number of speakers and angle between the first and last speakers. There is a maximum of 8 speakers for this configuration.

Surround

The surround multichannel configuration type is a speaker layout using five or more satellite speakers and a subwoofer for low frequencies. This arrangement is typically used for home theater applications and includes common layouts such as 5.1, 6.1, and two 7.1 variations. There is a checkbox in the editor that allows the lfe channel to be removed if desired. In the below diagram, the listener is placed in the center of the listening circle and is indicated with a small crosshair.

5.1	6.1	7.1 Front	7.1 Rear

Geometric

The geometric multichannel configuration type is a speaker layout where the speakers are configured in an evenly spaced geometry around the listener. There are four different geometric types based on 4, 5, 6, and 8 speakers.

Quadraphonic	Pentagonal	Hexagonal	Octagonal

Configuring Inputs

Input channel configuration is much less involved than outputs since only mono and stereo are supported. From the output configuration pane, click the Next button to configure the input tracks.

You may use the Add Input and Remove Input buttons to add and remove inputs respectively. Unlike outputs, a document is not required to have inputs.

Choosing the Audio Device

You may specify the audio device when you are creating a new document by clicking the Next button after configuring inputs You may use any audio device on your system such as your built-in audio hardware, an audio interface connected via firewire, a device connected via USB, or an aggregate device.

To select the device to use for your document, select the audio device from the Audio Device popup menu.

If your device supports changing the input source, you may select a source such as Internal Microphone or Line In using the Input Source popup button.

Note that most usb devices and some built-in computer interfaces have separate hardware for input and output. In these situations, only the output device will be visible in the Audio Device popup menu, and it will not be possible to create input tracks on such devices. It is recommended that you use an application such as Audio MIDI Setup to create an aggregate device comprised of the input and output hardware so that AU Lab sees this as a single device supporting both input and output.

Changing the Channel Assignments

The bottom of the dialog has a view that shows which input and output channels on the device each track is assigned to. Clicking on the Output Channels and Input Channels tabs switches the view between input and output. This view shows a visual representation of the numbers of channels available for the specified device. A stereo device such as the built-in audio has only two available channels, while a multichannel firewire device may have several channels grouped into discrete streams. For example, the device above shows a device that has ten (10) output channels all grouped as a single stream.

To change the channel assignments of a particular track, simply select the track to be moved, and drag it to a new location. For example, the image below shows an input track being moved from channels 1-2 on the device to channels 3-4:

In addition to changing channel assignments in a group, output channel assignments on the can be made on an individual basis. This is useful, for example, if you need to reorder your channel assignments on a multichannel device. To do this, uncheck the Link Channel Groups button. Note

Once channels have been unlinked, they can be moved individually:

Take care to ensure that none of the channel assignments overlap on the output section. Each individual channel has a label that indicates which speaker the output corresponds to. These are abbreviated as follows:

L	Left
R	Right
C	Center
Ls	Left Surround
Rs	Right Surround
Lrs	Left Rear Surround
Rrs	Right Rear Surround
Lc	Left Center
Rc	Right Center
LFE	Low Frequency Effects

NOTE: Default channel assignments for multichannel tracks are based on the device's preferred channel layout. An Application such as Audio MIDI Setup may be used to specify this default layout.

A document may have more output channels than supported by the device it is running on. For example, if you have selected Built-in audio for the source of your document, you may have a maximum of two output channels in use. Once these channels are used, any additional channel groups you create will be marked as Unused Channels. These channel groups will be created, but cannot be routed to an available output channel. If you were to change the source to a device that supports more than two output channels, you would then be able to move the group to a specific channel assignment on the multichannel device. To do this, drag the group from the unused channel section to the channels of the device that you want to use. Note that overlapping output channels are not allowed.

Unused channels on built-in audio	Unused channels on a multichannel device

This feature can be very useful because it allows the configuration of a document that has more output channels than the output device. At a later time, the document can be reconfigured on a multichannel device. The channel assignments will be preserved as the document is switched between devices.

Once you have completed configuration of the document, click the Done button to dismiss the assistant dialog and create the document. If at any time, you wish to make changes to the input or output track configurations, you can click the Back button to return to the previous pages and change the settings.

Saving Document Configurations

You can save and restore commonly used document configurations by clicking the Show Configurations button at the bottom of the dialog. This opens a drawer containing a list of all the document configurations available. To create a new configuration, first configure the input and output configuration and audio device and then press the + button at the bottom right corner of the drawer. Lastly, name the configuration.

To use an existing configuration, simply double-click on the name of the configuration, and then click the Done button.