3 Ardour will only ever deal with a single <dfn>audio device</dfn>. When it is
4 desired to use more than one audio device at the same time, there are two
9 <li>Use Ardour to start JACK (which handles all audio I/O), and create a
10 "fake" audio device which represents all the multiple devices to be used. How
11 to do this is platform dependent and described below.</li>
12 <li>Use a different tool to start JACK and manage all the devices.</li>
16 Ardour is fundamentally designed to be a component in a pro-audio/music
17 creation environment. Standard operating practice for such setups involves
18 using only a single digital <dfn>sample clock</dfn> (something counting off
19 the time between audio samples). This means that trying to use multiple
20 independent soundcards is problematic, because each soundcard has its own
21 sample clock, running independently from the others. Over time, these
22 different clocks <dfn>drift</dfn> out of sync with each other, which causes
23 glitches in the audio. This drift cannot be stopped, although in some cases
24 the effects may be insignificant enough that they might not be noticeable.
28 Thus, in an ideal world, a single device with a single clock and all the inputs,
29 outputs and other features needed should be used. Of course, there are those
30 who like to point out that this is not an ideal world, and believe that software
31 should make up for this.
37 In CoreAudio, <dfn>aggregate devices</dfn> provide a method to use multiple
38 soundcards as a single device. For example, two eight-channel devices can be
39 aggregated so that 16 channels can be recorded in Ardour.
43 Another example is using Soundflower to route audio to Ardour. To output the
44 audio through the speakers you will have to create an aggregate device to specify
45 Soundflower as the input and Built-in-Output as the output. In the Audio/MIDI Setup
46 in Ardour specify the aggregate device as both the Input and Output devices. And then
47 on the master track ensure you have specified the correct output channels. For example,
48 if you are using Soundflower(64) as input, Channels 65/66 will be the output
49 channels on your master track.
54 When using a <em>single</em> typical 3rd party audio interface (such as those
55 from Apogee, RME, Presonus, and many others), <em>or</em> using JackPilot or
56 a similar application to start JACK, there is no need to worry about any of
57 this. An aggregate device only needs to be set up if any of the following
61 <li>Two entirely separate devices are used <em>and</em> JACK is started using
63 <li>A <dfn>builtin audio device is used</dfn> <em>and</em> JACK is started
65 <li>More than two entirely separate devices are used</li>
70 In the case of a builtin audio device, an aggregate device that combines
71 "Builtin Input" and "Builtin Output" into one device needs to be created.
75 The precise instructions for creating an aggregate device on OS X have varied
76 from one released to another. Please read <a
77 href="https://support.apple.com/en-us/HT202000">https://support.apple.com/en-us/HT202000</a>.
83 Please see the instructions at <a href="http://jackaudio.org/faq/"
84 title="http://jackaudio.org/faq/">http://jackaudio.org/faq</a>.