User guide

100 Chapter 4 Setting Up Your System
Setting Up Core Audio Devices
Logic Express automatically recognizes any installed Core Audio hardware, and will use
the default settings—as defined in the Audio MIDI Setup utility (Applications/Utilities/
Audio MIDI Setup). It can, however, be advantageous to optimize the settings for your
individual hardware setup, particularly if you use several audio interfaces or a multiple
input/output device. This is done in the Logic Express > Preferences > Audio > Core
Audio tab.
Enabled
Click this box to enable the Core Audio driver.
Note: In situations where the preferred hardware is unavailable, such as when your
audio interface is not connected (or is turned off), Logic Express will automatically
select the built-in audio hardware of your Macintosh.
System Memory Requirement
The amount of free RAM required (outside the memory assigned to Logic Express) is
indicated here. The requirement value changes as you alter the parameters described
below.
Device
Allows you to choose between any installed Core Audio device, including the internal
sound hardware. This also includes aggregate audio devices, consisting of several audio
interfaces. See the Audio MIDI Setup Help for information on aggregate devices.
I/O Buffer Size
This parameter determines the size of the buffer used by the audio hardware—for both
input and output. The smaller the buffer size, the less latency you will encounter when
monitoring while recording, or using software instruments.
Some points to note:
 As this parameter value is reduced, it places a higher strain on the CPU(s) of the
system.
 There may be a point where the selected I/O Buffer Size is too small for your system,
and begins to affect playback. This usually takes the form of clicks, pops, and crackles
in your audio.
 You should, therefore, aim for the lowest possible I/O Buffer Size value that doesn’t
introduce these types of artefacts.
∏ Tip: If you find a higher I/O Buffer Size setting provides suitably low latency during
record monitoring and software instrument playback, you should use it. This will
minimize the impact on the CPU(s) of your system.