Apple Logic Pro 9 - Manual (Page 1275)

Note: When setting an output device which also provides inputs, the Input Device
setting changes accordingly. If choosing a different input device, you will be
recommended to use a common Word Clock for both audio devices, in order to ensure
the best sound quality.
• Input Device pop-up menu: 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 pop-up menu: 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 your system’s processor
or processors.
• 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 aim for the lowest possible I/O buffer size value that doesn’t introduce
clicks, pops, and crackles in your audio.
Tip: If you find that 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 your system’s processor or processors.
• Resulting Roundtrip Latency/Resulting Output Latency display: Displays either the resulting
roundtrip latency or the resulting output latency for the current I/O buffer size. Click
the display to toggle between the two values.
• Recording Delay slider: Allows you to delay the recording of audio by a certain fixed
value, helping you to compensate for any information delays that are caused by the
audio driver.
Note: You should not normally need to touch this parameter.
• Universal Track Mode checkbox: Universal Track Mode is turned on by default. It allows
you to play back stereo and mono regions on a single track. It should be left on.
You should only turn off Universal Track Mode if using DAE or TDM hardware. For more
information, see the Logic Pro TDM Guide.
• 24 Bit Recording checkbox: When this setting is turned on, Logic Pro can record 24-bit
files. 20- or 24-bit recordings offer a significant improvement in the available dynamic
range, but require high-quality peripheral components such as microphones and
pre-amps, not to mention high-quality analog-to-digital/digital-to-analog converters.
1275 Chapter 44 Preferences in Logic Pro