An Introduction to Computer Audio
Over the last decade computer sound
has come a long way, and a modern computer will include digital-media capabilities
rivaling or exceeding standalone CD and DVD players. Some of the technical aspects that
produce computer sound are rather obscure, and this article introduces the most popular
terminology and equipment you’re likely to bump into.
Sound cards
The fundamental audio component in a computer is its sound
card. Many computers (and all Macintosh models) include a sound card integrated directly
on the system’s motherboard. The main benefit of built-in sound is convenience, while
the main drawbacks are fewer features and possibly lower fidelity. PC users without
integrated audio, or those who want better sound, normally purchase PCI cards to upgrade.
Inputs and outputs
The standard connector to get sound out of a PC has become
the mini-jack, the 3.5mm or 1/8" plug also popular for plugging-in smaller
headphones. Speakers designed for PCs generally come with a mini-jack connector so you can
plug them directly in. You do need to be careful, as all of the other inputs and outputs
on a computer are also mini-jacks. Typically you’ll also find a line input, and there
may also be a microphone input. It’s easy to find an adapter cable that converts the
3.5mm mini-plug into the RCA jacks that you’re used to seeing on home stereo
components. They’re sold at most computer or electronics stores.
If your sound card’s outputs are color coded, the
green one will be the one to plug the speakers, headphones, or other output device into;
without colors to guide, you’ll have to decipher the cryptic symbols labeling each
one. Or, if you’re brave, just turn the volume down, start some music, and plug the
speakers into each jack until sound comes out.
Those who want to get their computer to record from an LP,
tape deck, or similar analog device will need to find the line input. You’ll also
need to carefully check the volume-control program on your computer to make sure that this
input is both enabled and has the volume turned up to be audible.
Many sound cards also include digital outputs, with both
the optical TosLink connectors as well as the coaxial ones that look like regular RCA
jacks. These digital outputs can support digital surround when playing back DVDs or other
applications.
CD-ROM and DVD-ROM drives
The CD drive in your computer will play both regular audio
CDs as well as CD-ROM media. Older systems required a small audio cable with a weird
connector to join the CD-ROM and the sound card. Newer ones instead use the digital-audio
capabilities of modern operating systems to pipe the CD audio over the computer’s
motherboard.
Many computers now ship with a DVD-ROM drive that does
everything the CD-ROM does, and you can also watch DVD movies and read DVD-ROM data. While
CD playback comes standard with all operating systems, your computer might not include
DVD-player software. Usually manufacturers include them with DVD-capable systems, and if
you add the DVD-ROM yourself the hardware manufacturer will often bundle a program to play
DVDs.
Surround sound
Here is the one area where PCs and home stereo equipment
are the farthest apart. A home-theater surround system will include Dolby Digital and
sometimes DTS surround playback. If you play DVDs on your computer and want to hear them
in surround, that too will require Dolby Digital or DTS support in both your sound card
and the DVD-player application. But, many of the games you might want to play on your PC
do not use Dolby Digital or DTS; instead, the sound cards include multiple two-channel
outputs, and you’re expected to plug a number of speakers into each of them.
Standards for generating surround-style sounds and similar "environmental audio"
within games include Microsoft’s DirectSound 3D and Creative’s EAX, neither of
which output Dolby Digital. So don’t expect that you can plug your PC into a home
theater and be able to hear the surround content on a game you’re playing; it’s
still a lot more complicated than that.
Since they weren’t shipping with digital outputs
necessary to support Dolby Digital, Macintosh computers were lagging a bit behind their PC
counterparts in terms of support for surround sound, and the older System 9 operating
system required some funky extensions even if you added a card with digital outputs. The
current OS X release of the Mac OS corrects most of these problems, but digital outputs
that support surround are still not as ubiquitous as they are on PCs.
External devices: USB and FireWire
There are a variety of sound-related devices that can sit
outside your computer. Most computers nowadays support the Universal Serial Bus for
connecting printers, scanners, and other devices. The older USB standard, USB 1.1, can run
at up to 12Mbps; that’s fast enough for many tasks but far slower than a hard drive.
Newer PCs include USB 2.0, which at 480Mbps can keep up with most hard drives and is
certainly more than fast enough for any audio-related task. Several companies make boxes
that work like a sound card but connect with USB 1.1 or 2.0.
The other popular standard for connecting external devices
is FireWire, also called IEEE 1394 or i.Link. FireWire normally runs at 480Mbps, and newer
hardware can even hit 800Mbps. All modern Macintosh computers use FireWire, while
it’s starting to show up more frequently in PCs. Adding a standalone FireWire PCI
card to an Intel PC or a Mac is very inexpensive.
If you see a digital camcorder with a computer interface on
it, that’s almost certainly a FireWire device. FireWire hard drives are also very
common nowadays, and their hot-swap ability means you can plug and unplug external drives
with a minimum of fuss. USB 2.0 shares this ability, as well as supporting similar speeds,
and USB 2.0 devices are usually cheaper than their FireWire equivalents.
Computer-audio file formats
Since computers have large hard drives nowadays, they can
hold a lot more data than you can put on the CD-ROM. There are a couple of formats you may
run across for storing audio files on a computer. Intel PCs hold uncompressed audio at
various quality levels in WAV files; Macintosh computers usually use the AIFF format for
the same purpose. At the full CD resolution of 16 bits/44.1kHz, the effective bit rate is
1376kbps, and a minute of audio takes up about 10MB worth of data.
MP3 is the most popular way to compress audio. A typical
good-quality MP3 track will be at 128kbps, around 1/10 the size of the CD original.
It’s possible to shrink MP3 files further, but sound quality drops substantially when
you do; 96kbps is approximately equal to cassette tape, 64kbps is like FM radio, while
32kbps might remind you of AM. Apple’s iTunes software bundled with Macs nowadays,
defaults to 160kbps.
Other audio-compression formats you’re more likely to
find only on PCs are Microsoft’s Windows Media Player WMP and Ogg Vorbis OGG files,
while Macs have recently started supporting the MPEG4 AAC standard. All of these formats
have less software support but sound somewhat better than MP3 files at the same bit rate.
Ripping audio
While technically called digital-audio extraction (DAE),
"ripping" has become the popular term for taking data off an audio CD and
putting it onto a hard drive. While some software is still aimed at doing so at full CD
quality, producing WAV or AIFF files on your computer, nowadays most ripping software is
aimed instead at going right from your audio CD into an MP3 file.
Even though it is technically a digital process, the audio
data on a music CD isn’t organized into data in a way that it can be easily read. If
the ripping process fails because the CD-ROM drive loses its position, the resulting file
will have skips or pops in the audio. Some software looks for this problem and will
re-read the disc to make sure this doesn’t happen. Many current-production drives
from companies that worry about such things can do perfect DAE at high speeds by combining
reliable audio-extraction circuitry in the hardware of the drive with an interface that
reports the amount of errors that occur when reading the disc (this is helpful for
scratched, dirty, or otherwise damaged originals). Good-quality CD-ROM drives can easily
extract audio perfectly at speeds 20 times above standard reading speed. This means that a
60-minute-long audio CD will rip to your hard drive in three minutes.
MP3 files include artist, title, and similar information
encoded into what are called ID3 tags inside the file. It’s possible to uniquely
identify audio CDs based on the exact contents of their table of contents, and there are a
few databases on the Internet that allow you to automatically fill in the identification
tags when ripping a CD into MP3 files. This considerably speeds up the process of
converting a collection of audio CDs into MP3s and should be considered an essential
feature if you’re doing that.
Recording onto CD-R
For years now, it’s been possible to use a CD recorder
to put music onto blank CD-R media by a process normally called burning. Normal media
holds 74 minutes worth of audio, and you can buy discs that pack the music a little
tighter than the official specification for CD and therefore hold 80 or 90 minutes.
Limited-capability CD recording software usually comes bundled with any drive you purchase
or with a computer that ships with a CD recorder.
One popular use of computer CD-R burners is to archive
out-of-print LPs and tapes. Tape decks should hook-up easily to your computer’s line
input. For LPs, you will need a standard phono preamp, because the signal that comes out
of a regular record player is very low. You can use a regular receiver as a phono preamp
if you hook up the record player normally and attach the computer to the receiver’s
tape output with an RCA-to-mini-jack cable.
Nowadays, even DVD-R burners are available for under $200,
which not only burn CDs, but can also make movies viewable on your home DVD player. Every
year your computer moves closer to the rest of your entertainment system, and that
continues to expand the capabilities of both systems synergistically.
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