Apple Logic Express 7 - Manual (Page 274)

274 Chapter 10 Audio Drivers
ReWire Behavior
When sending MIDI data to a ReWire compatible software instrument, you can choose
between four modes:
• Playback mode: use when playing back MIDI tracks via ReWire. This setting requires
less CPU power.
• Live mode: use when playing a ReWire instrument live. This settings requires more
CPU power.
Audio Engine
The Audio Engine is the part of Logic that processes and controls all audio data for
playback, recording, mixing, and effects.
All descriptions of the audio functionality in this manual are based on the Native Audio
Engine. Settings for different Audio Driver Models are nearly identical. This engine
performs a realtime, native Sample Rate Conversion.
Realtime Sample Rate Conversion
Any Sample Rate (Audio > Sample Rate) available in Logic can be used in the Native
Audio Engine—even if your audio hardware does not support the selected sample rate.
Nothing is lost in the process. All internal processing in Logic, including bouncing, is
performed at the original song sample rate (Audio > Sample Rate), and will be
performed independently of the sample rates supported by the audio hardware. Logic
automatically uses the best matching sample rate supported by your hardware for
playback.
This facility allows you to work on projects originally created on high-end audio
systems, with smaller setups.
Example:
A song was created on an audio hardware/setup at 96 kHz. Moving this project to a
laptop, or setup that does not support the original project’s sample rate, will commonly
result in the wrong playback speed of the audio files. The real time software sample
rate conversion facility will counteract this effect, allowing correct playback of the
project on the laptop, at any sample rate. You can start a Logic project in the studio,
continue on your laptop, and return to the studio with the new material.
Note: The set sample rate also applies for recording. As an example, if your audio
hardware supports sample rates up to 48 kHz, but the song is set to 96 kHz, Logic will
generate audio files at 96 kHz. You should be aware that the audio quality is not
improved in the process. The quality of audio is still at 48 kHz, as determined by the
recording hardware, despite the fact that the information is stored in a large 96 kHz file.
Important: Using higher audio sample rates often increases CPU load significantly.