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The DoorPost - GarageBand tips newsletter is sent to you every three months and is full of extra tips on how to get the most out of GarageBand. It takes a more in-depth look at some important aspects of digital audio and home recording with GarageBand. Also: Links to free loops, effects and software instruments.
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All about......
Creating an Aggregate Device

My friend was telling me something about making an Applegate something for GarageBand

I think your friend was talking about creating an AGGREGATE device

Yeah, the applegate device, how do I do that?

Let's start with the definition of aggregate:

An aggregate is a whole, formed by combining several (typically disparate) elements.

In this case what we're going to do is take several low cost, or free devices, and create one "virtual" multi channel input device. GB can only select a single device for input at a time, so to get around that we create this "Virtual Device" (our aggregate) which GB can use.

I like free.

Yes, I remember, Arty, and since we found out that you have a Line-In on your Mac, there's your freebie, and that gives you two channels of input right there (see: Recording 2 Tracks).

Now for this demonstration, in the the low cost category, I have a Logitech USB microphone which cost about US$20 and gives me 1 channel, and finally I have an iMic USB interface which cost around US$30 and gives me 2 channels.

So you can use all of these at the same time?

Yes, quite easily... I hate that word more and more ...shhh! We can set this up quickly in Audio MIDI Setup

I have to use another program?

Don't Panic, it takes just a few steps to complete

I'm not panicking. I'm not panicking

You're panicking, aren't you?


Well stop that and follow along...

Make sure Finder is active by clicking on its icon in the Dock repair 1

Open a new Finder Window
repair 2

Select "Utilities" from the "Go" Menu
repair 3

Find Audio MIDI Setup utility, and launch it

Once AMS is open, choose "open aggregate device Editor" from the audio menu.
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And you'll see a window like this

Press the agg 3 button, and a new aggregate device is created.

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Double click the highlighted text, and enter a new name for your aggregate device. I'm going to name mine with the three devices I intend to use so that it will be easy to see of what this virtual device consists. This might be important if I were to create several different aggregate devices for different purposes at a future date.
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Press return.

Now we can select the devices that we wish to add to our Aggregate Device.
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Notice that the iMic is listed twice, First as an output device, and then as an input device. Since we're creating an input device, we're only interested in the latter.

One important note to mention is that all the devices have to have the same sample rate to work together. In the case of GarageBand that means a 44.1K sample rate (See: Setting Sample Rates and Bit Depth)

Click the agg 7 button, and you can quit Audio MIDI Setup.

Now we are ready to make use of our new aggregate device in GarageBand. Open GarageBand's preferences.
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Click the agg 9 tab, and select your new aggregate device from the input popup menu

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When GarageBand asks you...
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Choose "Yes", wait a moment for the drivers to initialize, and now you can use any of the channels your Aggregate Devices consists of for multi-track recording.

Yeah, about that ... how exactly do I go about recording like that? Read through the Backstage Quickie: Recording Multiple Tracks, of course.

Of course!

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