OS X Audio Playback - Setup Guide
Benchmark's Guide for Audio Playback using Mac OS X
A simple guide to configure your computer for optimal audio quality
*this article was researched using OS X 10.4.6. Some information in this article may not apply to different versions of this software, though most information can be applied to most versions of OS X. Email us to report any errors or discrepancies, or if you would like more information on this topic.
Overview: OS X Audio
Bit-transparency is possible when using OS X for audio playback, but the user must configure the settings correctly. Specifically, the sample-rate of CoreAudio must be set manually within Audio MIDI Setup. It will not automatically change according to the sample-rate of the file being played. If the sample-rate is not set to match that of the audio file being played, the sample-rate will be converted, usually causing severe distortion. Other considerations about specifics media player are important as well. Please read the article pertaining to the specific media player being used.
Audio MIDI Setup
Mac OS X has an audio control interface called Audio MIDI Setup. This can usually be found in the 'Utilies' folder (Applications -> Utilities -> Audio MIDI Setup). We recommend adding an icon for 'AudioMIDI Setup' to the 'Dock' for instant access.
The settings in 'AudioMIDI Setup' determine what device will handle your audio input and output. It also sets the sample-rate and word-length of the input and output audio. This can be troublesome, especially if you have mixed playlists with different sample-rates.
Set Word-Length and Sample-Rate
It is recommended that the word-length always be set to the highest possible value (preferably 24 bit). The sample-rate should be set to the sample-rate of the audio you are listening to. If you're not sure about the sample-rate of an audio file, check the source disk, if possible. Audio CD's almost always have a sample-rate of 44.1kHz and word-length of 16-bit.
Set Volume Controls
All digital volume controls should be set to 1.00 (under 'Value' in Audio MIDI Setup). Depending on the nomenclature, it is also known as 0.0dB, or 100%, or 'Unity Gain'. Read more about how digital volume controls affect audio.
Known Problems for Audio with Mac OSX
Fixed output sample-rate
- The output sample rate does not automatically change to follow the sample rate of the file being played.
- The user must set output sample rate to match the sample rate of the file being played. Failure to do so will introduce severe distortion due to sample rate conversion.
- Playlists with mixed sample rates cannot be played without sample rate conversion.
THD+N due to sample-rate conversion and word-length truncation
We measured the distortion of a MacBook playing audio with iTunes through the optical (S/PDIF) output (which comes factory-built into the computer). The measurements indicate not only OS X performance, but iTunes as well. These distortion measurements illustrate how important it is to properly configure your software.
|This image is a graph of the optical (S/PDIF) audio output of the Macbook while a test tone is played through iTunes.
||This image is a graph of the optical (S/PDIF) audio output of the Macbook while a test tone is played through iTunes.
Articles about Computer Audio Setup
For more articles about specific media players and/or operating systems, see the Category:Setup Guides list of guides.