Computer Audio Interface
The line-in and headphone jacks on your computer are fine for occasional
recording and listening, but dedicated audio/MIDI interfaces like the one
shown in Figure 2.2 offer higher audio fidelity and more connection
options. They might also feature extras like bundled software.
Why not just use the audio I/O built into your computer? First, these inter-
faces usually lack the number and size of connections you need, and rarely
accommodate the lower signal level generated by guitars, microphones, and
turntables. Some computers lack sound inputs altogether. Second, built-in
interfaces tend to be too noisy for recording, especially if they’re not prop-
erly insulated against interference and computer noise. In addition, their
dynamic and frequency ranges often aren’t as good as those of dedicated
audio interfaces.
Interfaces for every budget and need are readily available, so your primary
job is to navigate three essential elements on the specifications sheet: inputs
and outputs (I/O), digital-to-analog (D/A) and analog-to-digital (A/D) con-
version quality, and the means by which the device communicates with
your computer (bus).
Figure 2.2 A hardware audio
interface, such as this Edirol
FA-101 Firewire interface,
shown here in front and rear
views, will be the primary
connection between your
computer’s audio software
and the outside world.
(Photo courtesy Edirol)
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Ins and outs of I/O
Since one of the primary reasons for buying an interface is to add additional
inputs and outputs, you’ll want to first think about what equipment you have
and how many inputs you’ll need to record simultaneously. For instance, if
you’re a vocalist playing an external keyboard, you’ll need one input for the
vocal mic and two for the external keyboard, for a total of three inputs. If
you need surround or other multichannel outputs, you’ll also need multiple
simultaneous outputs beyond the standard two-channel stereo. See Table 2.2
for some of the most common setups.
Audio Interface Checklist
Identify your needs and keep these elements in mind when youre buying an audio
Enough inputs for instruments, inputs and preamps for microphones
MIDI connection for MIDI devices (if needed)
Standard stereo pair
Multiple outputs for surround sound
Extra output for cueing (DJs only)
Extra output for alternate mixes for other musicians
Adequate resolution
16-bit, 44 kHz sample rate for everyday use
24-bit bit depth and 48 kHz, 96 kHz, or 192 kHz sample rates for high-quality
capture (see Chapter 1,“Understanding Digital Sound”)
Right bus for your computer
Laptops: CardBus, USB 1.1/2.0, or FireWire
Desktops: USB 1.1/2.0, FireWire, or PCI
OS compatibility
Drivers available for your OS of choice
Software bundles and hybrid devices (keyboards with integrated audio/MIDI
interfaces or audio interfaces combined with control surfaces) can add value.
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Myth dispelled:
users assume FireWire is
“better” than USB 1.1,
but that’s not exactly
right.With well-written
drivers, USB 1.1 can per-
form quite well in
recording and playback.
FireWire simply has
greater bandwidth than
USB 1.1, allowing more
Missing MIDI?
1x1 MIDI interfaces like
the M-Audio Uno have
MIDI at one end and
USB at the other.
Aside from analog audio I/O, other connections are necessary for hooking
up specific MIDI and digital equipment:
MIDI: If you have equipment with standard MIDI connections,
you’ll need either an audio interface with a MIDI connection or a
self-contained MIDI interface.
Digital Audio I/O: For a higher-quality audio signal and synchroniza-
tion, digital audio equipment often includes digital as well as analog
Chapter 3 explains different connection types and how to manage them.
Table 2.2 Typical Analog Audio Configurations
Number of Analog Connections Examples
Two in, two out Digidesign Mbox; Mackie Spike
Four in, four out M-Audio 410; Lexicon Omega
Eight in, eight out MOTU Traveler (; Edirol FA-101
Extras: All these interfaces also include digital I/O, and the 4x4 and 8x8 devices add MIDI.
D/A-A/D conversion
Specifications for bit depth and sampling rate are significant to audio quality,
as explained in Chapter 1, although 16-bit 44.1 kHz is sufficient for most
users. The quality of the digital audio circuitry itself plays a considerable
role as well, so you might want to check the reviews of an interface you’re
considering in pro audio publications like EQ and Sound on Sound. Some
pros even purchase pricey stand-alone D/A converters, although those with
home studios are more likely to use the converters built into their interface.
Connecting to your computer
Different interfaces connect to the computer via various connection types,
or buses, such as FireWire and USB (Table 2.3). Based on available band-
width, buses can offer multichannel audio with nearly real-time performance.
(Faster buses allow more channels.)

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