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iTunes & Computer Audio
Demystified
August 2011
What is Computer Audio?
Simply put, computer audio is the playback of digital music files from a
computer or hard drive-based storage device. Computer audio playback
can be as simple as playing those files on a portable media player like an
iPod, iPad, or a smart phone device such as the iPhone, or it can be as
sophisticated as a home entertainment system using a high-end Digital-to-
Analog Converter (DAC). Beyond that, computer audio is an ecosystem in
which all of our technology works together in flawless harmony to enhance
our collective music listening experience. Whether you’re a teenager lis-
tening to your new favorite, essential band, or a forty-year-old teleporting
himself back in time, computer audio is the gateway that delivers our music
with unprecedented quantity, quality and portability.
In this brave new frontier of computer-based digital audio, the current real-
ity is that a 256kbps MP3 compressed digital music file can sound better
than a mediocre LP, a lossless 16-bit/44.1kHz digital music file can sound
better than the CD it was ripped from, and a high-resolution 24-bit/88.2kHz
digital music file can truly offer a good-as or better-than vinyl sonic experi-
ence without our beloved vinyl’s flaws. Notice there is a bunch of “cans”
in the line above. This new world of iPods, computers and hard drives still
shares much with the familiar world of hi-fi knowledge and know-how driv-
ing the best path to performance. Great audio is possible in this new digital
music file world, but it is not automatic. Just as adjusting the stylus rake
angle properly is critical to getting the best performance from a turntable,
knowledge is required to optimize the hardware and software that will de-
fine the performance boundaries of your computer audio experience.
AudioQuest’s Computer Audio Demystified is a guide created to help you
navigate this transition from the compact disc player to file-based music
library management, and to get the computer you are storing your digital
music files on and your home entertainment system(s) on speaking terms.
Along the way will be easy instructions for getting the most performance
and convenience out of the music stored on your hard drive or computer.
With this guide we’re going to dispel some of the myths about computer
audio and teach you how best to acquire, rip, store and back up your digital
music library using iTunes, the most ubiquitous digital music management
system in the world today. Included will be links to setup guides for iTunes
for both Apple’s Mac OSX and Microsoft’s Windows operating systems.
We’re also going to offer some proven tips and techniques for enthusiasts
looking to use computer audio as the basis for a “best it can be” pursuit.
Computer audio is for every music lover at any and all budget and aspirational
entry points.
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Computer Audio Now
As Apple has demonstrated with iTunes, getting started
with computer audio is and should be fast and simple
regardless of whether you’re using a Mac or a Windows-
based PC. While the latest and greatest iterations of both
the Mac and Windows operating systems offer valuable
new computer audio enhancements, all that’s required to get started is a
computer running the Mac OSX 9 operating system or newer, or a PC
running Windows XP or newer. Getting your digital music library to your
home entertainment system(s) at its simplest can be a single run of HDMI,
Toslink optical, or even an analog mini to RCA stereo cable directly from a
computer. Or, instead of going directly from your computer to your home
entertainment system, you can also stream content from your computer to
a standalone set-top box connected to an AV receiver or surround processor.
Apple TV and Roku are great examples- a tiny box, one HDMI cable and
you’re in business. But the first step is to determine how you expect to
connect your computer to your audio system.
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Analog:
All modern computers are equipped with an internal
sound card and an analog 3.5 mm “headphone” output.
This terminal can be used to connect headphones, an
amplifier, or to connect a pair of powered desktop speakers
to the computer. This approach results in employing the computer’s
standard internal D-A conversion, which is typically not a high-perfor-
mance solution. Aftermarket sound cards with traditional stereo analog
outputs using RCAs can be purchased to improve performance.
S/PDIF:
(Sony/Philips Digital InterFace.) S/PDIF refers to
the coaxial and Toslink optical digital connections that have
become ubiquitous in the consumer electronics world,
featured on virtually every AV receiver and surround
processor manufactured since the 1990s and scores of external DACs.
Some computers come equipped with a Toslink or coax digital output.
Mac computers come with a headphone output that doubles as a
Toslink optical digital audio output when used with the appropriate
cable. If not, a S/PDIF output card can be added to your computer. In
addition, there are a number of devices available that will convert USB
to S/PDIF allowing computers to be used as a source for traditional
S/PDIF-equipped consumer electronics gear. S/PDIF is a unidirectional
(single direction) digital connection capable of transmitting digital
signals comprising a number of digital audio formats, including the
uncompressed 16-bit/44.1kHz PCM used to encode compact discs.
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S/PDIF has no defined data rate and is therefore compatible with
high-resolution digital music files up to 24-bit/192kHz. With S/PDIF the
original word clock is extracted from the digital audio data packet via a
PLL (Phase-Locked Loop receiver), which can be prone to jitter. However,
there are a number of sophisticated and mature solutions that correct
for jitter. Performance can be state of the art. S/PDIF offers a connection
that is reliable up to 20 meters in cable run length.
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HDMI/mini display port:
As HDMI has become the standard
digital audio/video interconnect among consumer electronics
components, many computer manufacturers recognize
this and consequently more computers are equipped with
this connection. HDMI provides bi-directional communication between
connected devices. If an HDMI device offers digital audio capability it is
required to support stereo PCM (uncompressed), the baseline format.
Clocking issues and jitter often hinder HDMI’s audio performance.
Other formats are optional, with HDMI allowing up to 8 channels of
uncompressed audio at bit depths up to 24-bits and sample rates as
great as 192kHz. HDMI also supports legacy compressed digital audio
formats such as Dolby Digital and DTS, and up to 8 channels of DSD
audio (the digital encoding used on Super Audio CDs). HDMI 1.3 and
1.4 support lossless compressed audio in the form of Dolby TrueHD
and DTS-HD Master Audio, each of which can support up to 7.1 channels
of high-resolution audio.
USB:
USB stands for Universal Serial Bus. All modern
Mac and Windows computers feature one or more USB
ports and include the necessary USB hardware and device
driver support. True to its name this is an honest to goodness
universal open standard. As a result, the number of computer audio
products on the consumer electronics market that use the USB
interface is substantial and growing. USB.org has established a set of
open standards that allows any manufacturer carte blanche access to
USB technology. USB offers bi-directional communication and excellent
audio performance potential as it has the ability to operate in either
asynchronous or adaptive transfer modes. These distinctions will be
explained in full later in this guide. USB cable runs are limited to 5 meters
unless a repeater or active USB-to-Ethernet converter is used.
FireWire:
FireWire, also known as IEEE1394, was developed
as a high-speed serial bus that can move large amounts of
data in real time at speeds of up to 800Mbps. For the
playback of digital music files FireWire offers excellent
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