Benchmark's Guide for Audio Playback using Mac
A Simple Guide to Configure Your Mac for Optimal Audio Quality
iTunes uses the audio engine built into QuickTime to play its audio (and video) files. In other words, iTunes is a sort of media file manager that plays its media using QuickTime, just like a website might play its media with QuickTime. Therefore, the information in this section will apply to both players, and we will address both players simultaneously.
Certain information within this article is very specific to the version of the software being used. Please check your software before acting on this information.
Set word length and sample rate to the highest settings of the audio interface
Word length should be set to the highest that the audio interface is capable, regardless of the word-length of the audio file being played.
Sample rate can be set to match the sample rate of the media or to the highest that the audio interface is capable, since the upsampling in iTunes is harmless
The sample-rate conversion in iTunes 7.X or 8.X will not add significant distortion to the audio. The user should not be discouraged from setting the sample-rate to 96 kHz as a permanent setting, even when the audio is less then 96 kHz.These settings can be set in QuickTime (even when using iTunes) by going to:
QuickTime->Edit->Preferences->QuickTime Preferences->Audio->Sound Out
Set iTunes volume to "Full"
Volume attenuation may cause severe distortion, depending on which version of iTunes you are using.
The volume controls in iTunes versions 7.X or 8.X will not cause significant distortion. The user should not hesitate to use the volume control in iTunes v7.x or 8.X
This does not refer to the track-specific "Volume Adjustment" settings found in the "Get Info" menu. The "Volume Adjustment" setting should always be set to "None" for all tracks.
Read more about how digital volume controls affects audio