Apple Logic Express 7 - Manual (Page 272)

272 Chapter 10 Audio Drivers
Enable
Click this box to enable the Core Audio driver.
Note: In situations where the preferred hardware is unavailable, such as when opening
a song created in the studio on your PowerBook, or your audio interface is not
connected or turned off, Logic will automatically select the built-in audio hardware of
your Macintosh.
Driver
Allows you to choose between any Core Audio Driver installed in your system,
including the internal sound output.
I/O Buffer Size
This parameter determines the size of the buffer used by the audio hardware—for both
input and output. Options range from 1024 down to 32 samples. The smaller the buffer
size, the less “latency” you will encounter when monitoring while recording, or using
software instruments.
Note: 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. You should therefore aim for the lowest possible I/O Buffer Size value that
doesn’t introduce these types of artefacts.
As this parameter value is reduced, it places a higher strain on the CPU(s) of the system.
On current model Macs, you should be able to reduce this value down to its minimum
value. As a word of advice, if you find a higher (larger) 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.
Recording Delay
This parameter is measured in samples. It allows the recording of Audio Regions to be
delayed by a certain fixed value. It helps advanced users to compensate for any
incorrect delay information that might be caused by the audio driver. You should not
normally need to touch this parameter.
Max. Number of Audiotracks
The Audio Engine requires free system memory, which is not assigned to Logic or any
other application. The amount of memory required depends on the maximum number
of tracks to be played, and on the number of I/O channels supplied by the driver. This
setting allows you to reduce the amount of memory required by the driver, by reducing
the number of tracks. This may be useful when you want to run other applications or
drivers simultaneously.