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ITunes-QuickTime for Mac - Setup Guide

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Benchmark's Guide for Audio Playback using Mac

A Simple Guide to Configure Your Mac for Optimal Audio Quality


Contents

Overview: iTunes-QuickTime

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.

Recommended Player Settings for Optimal Audio Quality

Set the correct sample-rate and set word-length to 24 bit

  • These are set in the 'Audio MIDI Setup' control interface, which is in the 'Utilities' folder:
(Applications -> Utilities -> Audio MIDI Setup).  
  • In the drop-down menu titled "Properties for:", select the output device which you are using
  • Under "Audio Output", the "Format" should be set to the appropriate sample rate and '2ch - 24 bit'.
    • For iTunes versions earlier then 7, we recommend setting the sample rate to match the sample rate of the media (music) being played
    • For iTunes versions later then 7, we recommend setting the sample rate to the highest sample rate that your device is capable of
    • For iTunes versions later then 7, iTunes must be launched after the sample rate is set in AudioMIDI. Any sample rate changes made in AudioMIDI while iTunes is open will not change the sample rate of iTunes until iTunes is re-launched. Consequently, it will cause CoreAudio to sample-rate convert the audio coming from iTunes. The result of CoreAudio sample-rate conversion is significant distortion.

Set iTunes volume to "Full"

  • Volume settings below "full" may cause severe distortion, especially on version 6 and earlier.
    • The volume controls in iTunes versions 7.X and 8.X will not cause significant distortion. The user should not hesitate to use the volume control in iTunes v7.x and 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

Bypass all audio DSP and plug-ins (EQ and any other audio 'enhancer')

  • For iTunes, disable 'Sound Enhancer' and 'Sound Check'
  • These settings can be found in iTunes by going to:
iTunes->Preferences->Playback

How to play FLAC files in iTunes

Article from Feedback Newsletter comparing iTunes 6 vs. iTunes 7

*this section of the article was written for Benchmark's "Feedback Newsletter" by John Siau. To receive emails with articles like these, subscribe to the "Feedback Newsletter".

iTunes 7.X seems to be a very good attempt at overcoming the limitations of CoreAudio. iTunes 7.X provides a high-quality 24-bit dithered volume control (the iTunes 6.X volume control was 16-bit with truncation problems). iTunes 7.X establishes a 24-bit connection with CoreAudio while iTunes 6.X was limited to 16-bit connections. iTunes 7.X attempts to avoid operating system based SRC services by providing its own very high quality SRC.

Our measurements show that the iTunes 7.X SRC is so good that it should be inaudible (unless it is down sampling). An easy, all-inclusive setup is to set AudioMIDI to 96kHz before launching iTunes and keep AudioMIDI at 96kHz. This will lock iTunes at 96 kHz, which will upsample all sample-rates lower then 96 kHz. Setting the default to 96 kHz would allow playback of high-resolution 96 kHz 24-bit files without any processing, and would utilize the high-quality iTunes 7.X SRC only when playing low resolution 44.1 and 48 kHz files, or the rare 88.2 kHz file.

Known Problems with iTunes v6 and QuickTime v7 for Mac

*this part of the article describes the performance of iTunes v6.0/ QuickTime v7.1. Most information in this article may not apply to different versions of this software. Email us to report any errors or discrepancies, or if you would like more information on this topic.

A 16-bit 10k sine wave played through iTunes v6 on OSX 10.4.6.  Ideally, this would have a 'flat' noise floor near -130 dBFS, with a single spike at 10 kHz.  This illustrations shows the distortion artifacts of sample-rate conversion from 48kHz to 44.1kHz and the volume control set near "50%" (-19dB).  As seen in the graph, there are distortion artifacts louder than 100dBFS!  It gets worse with 24-bit files!  See more iTunes distortion graphs
A 16-bit 10k sine wave played through iTunes v6 on OSX 10.4.6. Ideally, this would have a 'flat' noise floor near -130 dBFS, with a single spike at 10 kHz. This illustrations shows the distortion artifacts of sample-rate conversion from 48kHz to 44.1kHz and the volume control set near "50%" (-19dB). As seen in the graph, there are distortion artifacts louder than 100dBFS! It gets worse with 24-bit files! See more iTunes distortion graphs

Poor Sample-rate Conversion

Truncates all Word-length to 16-bit

Poor Volume Control

  • The volume control built into QuickTime and iTunes adds significant amounts of distortion, except when set to 100%.
  • See graphs of the distortion added to audio as a result of digital volume control when played with QuickTime and iTunes.
  • Read more about how digital volume controls affects audio

Articles about Computer Audio Setup

For more articles about specific media players and/or operating systems, see the Category:Setup Guides list of guides.

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